JPH08209284A - Cemented carbide and its production - Google Patents

Abstract

PURPOSE: To produce a cemented carbide improved in chipping resistance with hardly deteriorating its wear resistance and furthermore uniform in characteristics by forming its structure into the composite one in which either circumference of a hard phase and a soft phase is coated with the other. CONSTITUTION: The structure of a cemented carbide constituted of primary components of one or more kinds among the carbides, nitrides and carbon- nitrides of the group 4a, 5a and 6a in a periodic table and secondary components of one or more kinds among the Fe group and Cr group is constituted of a primary phase and a secondary phase with different hardness in combination, and the structure in which the circumference of the primary phase is coated with the secondary phase is formed. At this time, the diameter of the primary phase is preferably regulated to 20 to 300μm, the thickness of the secondary phase is preferably regulated to 5 to 50μm, and, with either as a hard phase and the other as a soft phases, the ratio of the hard phase is preferably regulated to 30 to 90vol.%. This hard alloy can be produced by granulating the primary phase material individually, coating the surface of the grains with the secondary phase material and thereafter compacting and baking.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cemented carbide having improved fracture resistance without impairing wear resistance.

[0002]

2. Description of the Related Art Conventionally, materials such as cast steel and tool steel have been used for, for example, rolling members. These materials have high toughness and excellent impact resistance, but low wear resistance. There is a problem that the service life is short. On the other hand, cemented carbide, which currently occupies an important position in the field of cutting tools, is WC
It is known as a material excellent in wear resistance, impact resistance, and fracture resistance because it contains carbides, nitrides, or carbonitrides of Ti and Ti as the main components.

Therefore, recently, in the field where cast steel and tool steel have been conventionally used, when more wear resistance is required, a cemented carbide having higher wear resistance, for example, WC-Co. Cemented carbides are beginning to be used. However, the hardness of WC is about Hv2400, and a material with higher hardness is required to further improve wear resistance.

As another cemented carbide, a WC-TiC-Co type sintered alloy (cermet) is known. Since TiC itself has an excellent hardness of Hv2930, the cermet using it has better wear resistance than the WC-based sintered alloy. However, in general, WC-TiC-Co
Although the base-based sintered alloy has excellent wear resistance, it has a defect of poor fracture resistance. Therefore, when the WC-TiC-Co based sintered alloy is applied to, for example, a rolling roll, there is a problem that cracks are easily generated on the surface of the roll and the crack easily propagates to the inside.

Further, in recent years, in order to increase the tool life, a technique of forming a hard coating film of a carbide of a 4a, 5a or 6a group metal on the surface of a cemented carbide has been proposed and implemented. However,
In this type of coated cemented carbide, the hard coating layer is more brittle than the cemented carbide, and especially when the hard coating layer is formed by the chemical vapor deposition method, the toughness of the coated cemented carbide is lower than that of the base metal. There is a problem that the hard alloy is easily damaged.

In order to solve this problem, the periodic table 4a,
On the surface of a hard alloy substrate containing one or more of carbides, nitrides, and carbonitrides of 5a and 6a metals and a metal such as Co, it is more tougher than the substrate and soft and hard. A continuously increasing intermediate layer is provided toward the inside, on which carbides, nitrides, carbonitrides of 4a, 5a and 6a metals are provided.
There is disclosed a cemented carbide tool coated with one or more single-layer or multiple-layer hard layers of oxides, oxycarbides, oxycarbonitrides, and aluminum oxides (JP-A-53-131909).
No.). However, there is a problem in that the propagation of cracks generated in the hard layer is stopped by the intermediate layer and the fracture resistance is improved, but the wear resistance is reduced.

In order to solve this problem, one of the applicants of the present invention made the cemented carbide base material a two-phase structure of a hard phase and a soft phase, and formed a hard coating layer on it to reduce wear resistance. We have provided a coated cemented carbide with improved fracture resistance without any damage (see Japanese Patent Publication No. 5-55598).

[0008]

Even in the case of the alloy containing the hard phase and the soft phase described above, basically the two phases are uniformly dispersed, but if the hard phases are partially gathered, the fracture resistance is high. There is also a problem in that the abrasion resistance may be a problem when the soft phase is partially gathered. An object of the present invention is to provide a cemented carbide having improved fracture resistance with almost no deterioration in wear resistance and having uniform properties.

[0009]

DISCLOSURE OF THE INVENTION The present inventor has found that the cemented carbide has a two-phase structure of a first phase and a second phase having different hardness, and the peripheral portion of the first phase is covered with the second phase. It has been discovered that, by setting the above, it is possible to significantly improve the fracture resistance without substantially lowering the wear resistance, and further to make the characteristics more uniform in any place of the cemented carbide material, and have arrived at the present invention. .

That is, in the present invention, in a cemented carbide, two kinds of phases having different hardnesses are compounded, and the two phases are the first components of carbides, nitrides and carbonitrides of the 4a, 5a and 6a groups of the periodic table. One or more of the products, and Fe as the second component
It is characterized in that it is composed of one or two or more members of the group Cr and the group Cr, and that the second phase covers the peripheral portion of the first phase.

The cemented carbide having the above structure has extremely high fracture resistance. The reason for this is not necessarily clear, but it is difficult for microcracks generated during use to propagate due to the complicated internal structure of the cemented carbide of the present invention consisting of the first phase and the second phase having different hardness in the peripheral portion thereof, It is also considered that the propagation energy of cracks is consumed due to propagation through a complicated route.

Further, by covering the periphery of the first phase with the second phase having different hardness, the high hardness portion (hard phase portion) and the high toughness portion (soft phase portion) are paired and finely and uniformly distributed. As a result, the variation in characteristics depending on the location is reduced. For example, using the cemented carbide of the present invention as a cutting tool,
When cutting at 2.0 mm and feed rate of 0.4 mm / rev., The location of the cutting edge that comes into contact with the work material is approximately 2 mm width × 0.4 mm, but the pair of high hardness part and high toughness part existing in this area is About 5 to 500 pairs. The smaller the diameter of the first phase portion and the narrower the width of the second phase portion, the larger the logarithm of the high hardness portion / high toughness material portion that hits the material to be cut, and the variation in the characteristics of hardness and toughness is effectively reduced.

When the structure of the cemented carbide has a granular composite structure in which the first phase serves as the nucleus and the second phase covers the periphery thereof, the above effect becomes more remarkable. The size of the first phase portion is 20 to 300 μm in diameter, preferably 20 to 200 μm.
If the diameter exceeds 300 μm, the logarithm of the high hardness portion and the high toughness portion effective during cutting becomes extremely small, resulting in large variation in characteristics, which is not suitable. On the other hand, if the size of the first phase portion is 20 μm or less in diameter, molding by pressing or the like becomes difficult, which is industrially inappropriate.

The peripheral portion of the first phase portion has a thickness of 5 to 50 in the second phase portion.
It can be evenly coated with a thickness of μm, preferably 5-30 μm. The thickness of the second phase part needs to be 5 μm or more to prevent the propagation of cracks described above. If it exceeds 50 μm, the second phase part becomes too thick, and the balance with the first phase should be considered. Is inappropriate. Considering the actual cutting conditions, the diameter of the first phase is preferably 20-200 μm and the width of the second phase is 5-30 μm in order to further improve the uniformity of the characteristics.
m is preferred.

When the first phase is a hard phase and the second phase is a softer phase that is softer than the hard phase, it has excellent toughness, few cracks are generated, and it is difficult for the cracks to propagate. Especially excellent in defects. When the second phase is a hard phase and the first phase is a softer phase that is softer than the hard phase, it is suitable for applications in which the overall rigidity is high and high strength and high wear resistance are required. is there. In this case, fine cracks are generated on the surface portion and the like, but the cracks are difficult to propagate through the hard phase formed in a complicated manner, and therefore the fracture resistance is excellent.

The hard phase and the soft phase forming the first phase and the second phase of the cemented carbide each contain the first component and the second component, and are classified according to the type, ratio and particle size of the first component. . The hard phase and the soft phase are, for example, the following combinations. (A) Hard phase: Contains a large amount of harder components among the first components. Soft phase: The proportion of harder components in the first component is small. (B) Hard phase: Contains a relatively large amount of the first component. Soft phase: Contains a relatively small amount of the first component. (C) Hard phase: The average particle size of the first component is relatively small. Soft phase: The average particle size of the first component is relatively large.

In the case of (A): The hard phase and the soft phase both contain the first component and the second component, but the proportion of the harder component in the first component is different. The main components of both phases are WC, TiC, TiN, T
Examples are aC, NbC, TiCN, ZrC and VC. The hardness of TiC, TiN, NbC, and VC is higher than that of the main components such as WC. A phase containing a large amount of these harder components is a hard phase, and a phase containing a small amount is a soft phase.

In the case of (B): Unlike the case of (A), the amount of the first component is different even if it is the same. For example, both phases each contain a first component consisting of WC and a second component such as Co,
The hard phase contains a larger amount of the first component than the soft phase. In addition to both relatively soft components such as WC and TaC, TiC and Z
It may contain relatively hard components such as rC, HfC, VC, and NbC. The ratio of the first component in both phases must be such that the cemented carbide matrix is clearly two-phase.

In the case of (C): Even if the base material is composed of the first component and the second component, if the particle size of the first component is different, it is divided into two phases. The phase containing the first component having a small particle size is a hard phase, and the phase containing the first component having a large particle size is a soft phase. Although the difference in particle size is relative, generally the average particle size of the first component in the hard phase is 0.4 to 6 μm, preferably 0.6.
~ 5 μm, the average particle size of the first component in the soft phase is 0.6 ~
It is 10 μm, preferably 0.8 to 6 μm.

In the case of the present invention, the above cases (A) to (C) may occur simultaneously. For example, one phase contains a relatively large amount of relatively hard components, but the first component has a large particle size, and the other phase contains a relatively small amount of relatively hard components, but the first component has a small particle size. There are cases. In such a case, it becomes a problem which phase is hard. Although it is not easy to completely derive the hard-soft relationship in all such cases, it can be said that the order of (B), (C), and (A) is generally the highest in order of effectiveness. The hard phase portion is 30 to 90 vol%. If the hard phase portion is less than 30 vol%, the wear resistance becomes low, and if the hard phase portion exceeds 90 vol%, the amount of the soft phase portion is small and sufficient toughness cannot be obtained.

When Co is used as the second component of the hard phase and the soft phase, if the difference in Co content between the two phases is reduced to within ± 3%, the Co is distributed throughout the cemented carbide base alloy and The overall toughness and uniformity are increased. As described above, since the first component of the hard phase is composed of one or more of TiC, TaC, WC, TiN, TiCN, NbC, ZrC and VC, a phase with higher hardness can be obtained. Can be formed. Further, by forming the soft phase with an alloy based on WC, it is possible to form a soft phase having higher toughness.

The surface of the cemented carbide of the present invention is a carbide, a nitride, a carbonitride, an oxycarbide, an oxynitride, an oxycarbonitride and an oxide of a metal of group 4a, 5a, 6a of the periodic table. Further, the wear resistance can be further improved by coating a single layer or a multi-layered film of two or more selected from oxides, nitrides and oxycarbides of Al and Al. The material for coating such cemented carbide consists of carbides, nitrides, carbonitrides, oxycarbonitrides and oxides of groups 4a, 5a and 6a of the Periodic Table and oxides of Al and oxides, nitrides and oxycarbides. Selected from the group. Preferably TiC, TiN, TiCN, Al ₂
O ₃ etc. The coating layer can be formed by various methods, but from the viewpoint of strength, the chemical vapor deposition (CVD) method is preferable. In addition to this, the ion plating method is also effective. As the coating layer, a film of TiC, TiN, TiCN, Al2O3 or the like is used in a single layer or multiple layers. For single layer, the thickness is 0.5-20μ
m, preferably 1 to 15 μm. In the case of multiple layers, the total thickness is 0.8 to 20 μm, preferably 1 to 15 μm.

The method for producing the cemented carbide of the present invention is as follows: the hard phase material having the above-mentioned components is granulated alone, and the individual hard phase particles are covered with the soft phase material having the above-mentioned component. , Molding and firing. By using such a manufacturing method, the cemented carbide of the present invention having a structure in which the hard phase is covered with the soft phase can be manufactured.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described with reference to the following examples. (Example 1) (TiC + TaC + NbC) = 9.0 wt%, Co = 6.0 wt%, balance
Granulated powder having an average particle size of 150 μm was produced from a powder having a composition of WC (WC particle size 4.0 μm) (hard phase composition) by a ball mill mixing, drying and granulation process. Next, the surface of the granulated powder was Co = 20 wt% and the balance W by the pan coating method.
Coated with powder having a composition of C (WC grain size 5.5 μm) (soft phase composition), core material (hard phase composition) and coating material (soft phase composition)
Granulated powder of the core material / coating material was produced at a mixing ratio shown in Table 1 consisting of

[0025]

[Table 1] Note 1) Fracture resistance ◯: No fracture, ×: There is a fracture 2) Cutting life (average flank wear amount 0.3 mm)

The produced granulated powder of the core material / coating material was die-molded and vacuum-sintered at 1350 to 1400 ° C. to produce a cemented carbide base material composed of a hard phase / soft phase. The base material is a TNMN432 slow-away tip. With the above cemented carbide as the base material, CV
After coating the surface with TiC 5 μm by D method, a coated cemented carbide with Al 2 O 3 coated 2 μm was prepared.

Cemented carbide hard phase 50 produced in this way
%, A soft phase of 50% is shown in FIG. Table 2 shows the measurement results of the Vickers hardness and the composition at each point shown in FIG. The Vickers hardness was measured under a load of 1 kg, and the composition was analyzed by EDX.

[0028]

[Table 2]

From FIG. 1, it can be seen that a white soft phase covers the area (hard phase) having a diameter of 80 to 200 μm where many black particles are gathered. From Table 2, the Vickers hardness of the hard phase part is 1650, the hardness of the soft phase part is 1450, the composition of the hard phase has a large amount of Ti and Ta, and the soft phase has W and Co.
It can be seen that it is formed from and. The amount of Co is a hard phase
It was 9.5 wt% and 12.0 wt% in soft phase. The width of the soft phase depends on the volume ratio of the hard phase and the soft phase, but is approximately 5 to 50 μm.

The fracture resistance of the coated cemented carbide of the present invention was evaluated by a cutting test under the following conditions. Work material: SCM440 (Hs38), intermittent cutting with four grooves Cutting speed: 100 m / min Cutting depth: 2.0 mm Cutting time: 3 minutes Wear resistance was evaluated under the following cutting conditions. Work material: SCM440 (Hs38), continuous cutting Cutting speed: 180 m / min Depth of cut: 2.0 mm Feed: 0.4 mm / min Wet cutting (W-1 type-2)

For comparison, the fracture resistance and wear resistance of a cemented carbide consisting of the above hard phase and soft phase coated with a TiC / Al ₂ O ₃ film under the same conditions are compared with those of the present invention. The results of evaluation under the same conditions are shown in Table 1. The product of the present invention has an excellent balance of fracture resistance and wear resistance as compared with the comparative product, and in particular, the effect of the composite phase is remarkable in the range of 30 to 90 vol% of the hard phase and the soft phase, and the fracture resistance of the soft phase is remarkable. It can be seen that the wear resistance of the hard phase can be secured while maintaining the properties.

(Example 2) (TiC + TaC + TiN + TiCN + ZrC) = 11.
From a powder having a composition (hard phase composition) of 0 wt%, Co = 7.0 wt% and the balance WC (WC grain size 4.1 μm), ball mill mixing, drying,
After producing a fired body by granulating and firing at 1400 ° C. for 1 hour, the fired body was pulverized again to obtain a powder having an average diameter of 40 μm. Next, this sintered powder is fluidized and suspended by a vertical turbulent air flow in a coating chamber of a coating device by an air suspension method, and its surface is coated with a soft composition for coating. By spraying the alcohol solution in which the powder is dispersed and immediately drying, the sintered powder (hard phase composition) is used as the core material, and the coating material of the soft composition is averaged around it.
It was coated by a thickness of μm. The composition of the soft phase powder is
Co = 9.0 wt%, balance WC (WC grain size 3.5 μm).

The prepared core / covering material granulated powder is molded into a mold, vacuum-sintered at 1350 ° C. for 1 hour, and then HIP-baked at 1000 ° C. and 1500 atm to form a hard phase / soft phase book. A cemented carbide base material of the invention was produced. The base material shape is a SPK42TR slow-away tip. Using the above cemented carbide as a base material, TiC of 2 μm was coated by the CVD method, and then a coated cemented carbide was prepared in which TiCN of 5 μm and TiN of 2 μm were coated. The cemented carbide base material thus produced was evaluated in the same manner as in Example 1. The average diameter of the hard phase is 40 μm, and the average thickness of the soft phase around it is 5 μm.
The Vickers hardness of the central part of the hard phase was 1600 and the hardness of the soft phase part was 1250. As a result of evaluation by EDX, the composition of the hard phase was found to have a large amount of Ti and Ta, and the soft phase was formed of W and Co. The amount of Co is 7.0 wt% in the hard phase and 9.0 in the soft phase.
It was wt%.

The fracture resistance of the coated cemented carbide of the present invention having a hard phase portion of 50 vol% was evaluated by milling under the following conditions. Work material: SKD11 (Hs55) Cutting speed: 150m / min Depth of cut: 3.0mm Cutting length: 700mm max. Also, for comparison, it consists of hard and soft phases produced under the same conditions as the product of the present invention. A comparative cemented carbide coated with a TiC / TiCN / TiN film under the same conditions was evaluated for fracture resistance and wear resistance under the same conditions as the product of the present invention. Table 3 shows the mixing ratios of the hard phase raw material and the soft phase raw material of the product of the present invention and the comparative product and the evaluation results by the cutting test.

[0035]

[Table 3] Note 1) Fracture resistance ◯: No fracture, ×: There is a fracture 2) Cutting life (average flank wear amount 0.3 mm)

It can be seen that the product of the present invention has a better balance of fracture resistance and wear resistance than the comparative product, and the wear resistance of the hard phase can be secured while maintaining the fracture resistance of the soft phase.

(Example 3) (TiC + TaC + NbC) = 9.0 wt%, Co =
Granulated powder having an average particle size of 150 μm was produced from a powder having a composition (hard phase composition) of 3.0 wt% and the balance WC (WC particle size 4.0 μm) by a ball mill mixing, drying and granulating process. Next, the surface of this granulated powder was subjected to a pan coating method.
Co = 20 wt% and the balance WC (WC particle size 5.5 μm) is coated with a powder having a composition (soft phase composition), and the core material (hard phase composition) and the coating material (soft phase composition) are mixed 50:50. Core material in proportion
A granulated powder of the covering material was prepared.

The granulated powder of the prepared core material / coating material is die-molded and vacuum-sintered at 1350 to 1400 ° C. to produce a cemented carbide roll having a hard phase / soft phase with a diameter of 80 mm and a length of 70 mm. did. As a result of evaluation by EDX, the composition of the hard phase of the cemented carbide roll thus produced was found to have a large amount of Ti and Ta, and the soft phase was formed of W and Co. The amount of Co is 7.5 in the hard phase
wt% and 13.5 wt% in the soft phase. Further, for comparison, a comparative cemented carbide roll composed of only the above hard phase and soft phase was prepared.

The fracture resistance of the cemented carbide of the present invention and the comparative roll was evaluated by a rolling test under the following conditions. Rolled material: SUS304 Rolled material dimensions: 1.0 mm thickness x 15.0 mm width x 25
Length of 0 m Rolling temperature: 900 ° C. Rolling speed: 150 m / min Rolling reduction ratio: 30% The product of the present invention has no wear in the rolled portion even after the above rolling. It showed good skin. On the other hand, among the comparison rolls, the cemented carbide roll consisting of only the hard phase had a large number of cracks on the surface of the rolled part due to the impacts when the material to be rolled was caught and at the end of rolling. Further, among the comparative rolls, the cemented carbide roll consisting only of the soft phase had abrasion due to the material to be rolled in the rolling part, and it was necessary to carry out cutting.

(Example 4) Co = 20 wt%, balance WC (WC grain size)
Powder having a composition (soft phase composition) of 5.5 μm)
Average particle size of 150 μm due to the mixing, drying and granulating process
Granulated powder of was produced. Next, the surface of this granulated powder was subjected to a pan coating method to obtain (TiC + TaC + NbC) = 9.0 wt%, Co = 3.0
Coating with powder having a composition (hard phase composition) of wt% and the balance WC (WC particle size 4.0 μm), the core material (soft phase composition) and the coating material (hard phase composition) were 50:50, contrary to Example 3. Granulated powder of the core material / coating material was prepared at a mixing ratio of

The granulated powder of the prepared core material / coating material is die-molded and vacuum-sintered at 1350 to 1400 ° C. to produce a cemented carbide roll having a hard phase / soft phase and having a diameter of 80 mm and a length of 70 mm. did. As a result of evaluation by EDX, the composition of the hard phase of the cemented carbide roll thus produced was found to have a large amount of Ti and Ta, and the soft phase was formed of W and Co. The amount of Co is 7.5 in the hard phase
wt% and 13.5 wt% in the soft phase.

The fracture resistance of the cemented carbide of the present invention was evaluated by a rolling test under the following conditions. Rolled material: SUS304 Rolled material dimensions: 1.0 mm thickness x 15.0 mm width x 25
0 m length Rolling frequency: 2 times Rolling temperature: 900 ° C. Rolling speed: 150 m / min Rolling reduction ratio: 30% In the product of the present invention, even after the above rolling, the rolling part was not worn, but fine cracks were generated on the surface. I was doing it, but it wasn't enough to require refurbishment.

[0043]

According to the present invention, regarding the improvement of fracture resistance, which is a problem of the present cemented carbide, it is effective in significantly improving fracture resistance with almost no loss in wear resistance, and
It is possible to produce cemented carbide with stable quality with little variation in characteristics due to location.

[Brief description of drawings]

FIG. 1 is an optical micrograph of the structure of a cemented carbide according to the present invention.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication location // C23C 16/30 (72) Inventor Hiroaki Inoue 13 Hitachi, Ltd. Narita, Chiba Prefecture 2 Hitachi Tool Co., Ltd. Ceremony Company Narita Factory (72) Inventor Tatsuya Sakamoto 2 Hitachi Tool Co., Ltd., 13 Narai, Narita, Chiba Prefecture Formula Company Narita Factory (72) Inventor Shigenobu Adachi 2 Hitachi Tool Co., Ltd. Narita, Chiba Prefecture Narita Factory

Claims (12)

[Claims] 1. A composite of two kinds of phases, a first phase and a second phase having different hardnesses, said two phases being the first component of the periodic table 4
One or two of a, 5a, 6a carbides, nitrides, carbonitrides
One or more kinds, and as a second component, one or more kinds of Fe group and Cr group, and the second phase covers the peripheral portion of the first phase. alloy. 2. The cemented carbide according to claim 1, wherein the structure of the cemented carbide has a granular composite structure in which the first phase serves as a nucleus and the second phase covers the periphery thereof. . 3. The cemented carbide according to claim 1, wherein the first phase has a diameter of 20 to 300 μm. 4. The cemented carbide according to claim 1, wherein the second phase has a thickness of 5 to 50 μm. 5. The cemented carbide according to claim 1, wherein the first phase is a hard phase and the second phase is a soft phase softer than the hard phase. alloy. 6. The cemented carbide according to claim 1, wherein the second phase is a hard phase and the first phase is a soft phase softer than the hard phase. alloy. 7. The cemented carbide according to claim 5 or 6, wherein the hard phase occupies 30 to 90 vol% of the whole. 8. The cemented carbide according to claim 5, wherein the difference in the amount of Co between the hard phase and the soft phase is within ± 3%. 9. The first component of the hard phase is TiC, TaC, WC, Ti.
The cemented carbide according to any one of claims 5 to 8, which is composed of one or more of N, TiCN, NbC, ZrC, and VC. 10. The cemented carbide according to claim 5, wherein the soft phase is composed of an alloy based on WC. 11. The surface of the cemented carbide is coated with 4a, 5 of the periodic table.
Single or two or more multi-layer coatings selected from carbides, nitrides, carbonitrides, oxycarbides, oxynitrides, oxycarbonitrides and oxides of Al and oxides of group a and 6a metals. The cemented carbide according to any one of claims 1 to 10, characterized by being coated with. 12. The method according to claim 1, wherein the first phase material is independently granulated, and then the individual first phase particles are covered with the second phase material, and then molded and fired. Item 11
The method for producing a cemented carbide according to any one of 1.