JP2003094207A - Cutting tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cutting tool retaining high hardness and toughness having excellent wear resistance, plasticity and deformability resistance and fracture- ability resistance for high efficient cutting of a hard cutting material such as stainless steel or the like. SOLUTION: This cutting tool is characterizedly having a superficial region having a minimum hardness of 90-98% in comparison with the internal hardness of a parent material in the vicinity of the surface of the parent material of cemented carbide in the cutting tool having a clad layer on the surface of the cemented carbide comprising a rigid phase component greater than the first class of metallic carbide, nitride and/or carbo-nitride selected among group 4a, 5a, 6a metals in the periodic table including at least WC and a binder phase component at least one kind of the iron group metals.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cutting tool, and more particularly to a cutting tool made of a tungsten carbide based coated cemented carbide base material having hardness and toughness suitable for cutting difficult-to-cut materials such as stainless steel.

[0002]

2. Description of the Related Art Conventionally, a cemented carbide that has been widely used for metal cutting is a WC-based alloy composed of a hard phase mainly composed of tungsten carbide and a binder phase of an iron group metal such as cobalt.
The Co-based alloy, or the above WC-Co system, has a periodic table
Systems in which carbides, nitrides, carbonitrides, and the like of a, 5a, and 6a group metals are added are known. These cemented carbides are mainly used as cutting tools for cutting cast iron, carbon steel, etc., but recently, they are also being applied for cutting difficult-to-cut materials represented by stainless steel. However, these difficult-to-cut materials have many problems in the field of cutting work because of their properties of occurrence of work hardening, low thermal conductivity and high affinity with tool materials. That is, a cemented carbide base material having both toughness and hardness was required for processing stainless steel.

[0003]

[Problems to be Solved by the Invention] A conventional cutting tool made of K type cemented carbide made of WC-Co type cemented carbide having a relatively small amount of Co and made of P type cemented carbide having a B1 type solid solution of a single composition. When cutting difficult-to-cut materials such as stainless steel with a cutting tool, the wear of the cutting tool progresses rapidly and defects that are thought to be caused by welding occur and the work surface condition of the work material deteriorates There was a problem that the tool life was reached and good cutting could not be performed.

Further, the cutting resistance received from the work-hardened working surface causes severe damage to the primary boundary portion, the tool life is quickly reached, and good cutting characteristics are not obtained.

The present invention solves the above problems and provides a cutting tool made of coated cemented carbide which can be used as a cutting tool suitable for high speed and high efficiency cutting of difficult-to-cut materials typified by stainless steel. The purpose is to do.

[0006]

As a result of repeated studies on the above-mentioned problems, the present inventor found that the minimum hardness of 90 to 98% was found in the vicinity of the surface of the cemented carbide base material as compared with the hardness inside the base material. By having a surface region, it is possible to obtain a cemented carbide base material that has sufficient hardness when processing difficult-to-cut materials and also has toughness that can withstand the impact received when cutting the work-hardened surface. The present invention was obtained.

In the cemented carbide base material, there are two or more kinds of B1 type solid solution phases inside the base material, and at least one of the B1 type solid solution phases is compared with other B1 type solid solution phases. It was found that the above effects are characteristically obtained by the B1 type solid solution phase containing a large amount of Zr, and the existence states of these being different near the surface of the cemented carbide base material and inside the base material. .

That is, the cutting tool of the present invention comprises at least one kind of carbide, nitride and / or carbonitride of a metal selected from the group consisting of Groups 4a, 5a and 6a of the Periodic Table containing at least WC. In a cutting tool having a coating layer on the surface of a cemented carbide base material composed of a hard phase component and a binder phase component of one or more iron group metals, a hardness inside the base material near the surface of the cemented carbide base material By comparison, it is characterized by having a minimum hardness region of 90 to 98%.

The above cutting tool has the above-mentioned periodic table Nos. 4a and 5a.
The metal containing Zr as a metal selected from the group consisting of groups a and 6a, and the ratio of Zr in the metal selected from the group consisting of groups 4a, 5a and 6a of the periodic table is the cemented carbide matrix. It is desirable to have a region higher than the inside of the material near the surface of the cemented carbide base material.

Further, in the above cutting tool, the thickness of the region where the ratio of Zr is higher than that in the inside of the cemented carbide base material is 5
To 100 μm is desirable.

Further, in the above cutting tool, two or more kinds of B1-type solid solution phases are present inside the cemented carbide base material,
It is desirable that one of the type 1 solid solution phases is a type B1 solid solution phase having a higher Zr content than the other type B1 type solid solution phases.

In the above cutting tool, it is desirable that the average particle size of the B1 type solid solution phase containing a large amount of Zr is 3 μm or less.

In the above cutting tool, the periodic table 4a,
Ta of metals selected from the group consisting of 5a and 6a groups
Even if the content of is less than 1% by weight based on TaC, the cemented carbide base material has excellent tool characteristics.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below. The cemented carbide base material used for the cutting tool of the present invention is composed of a hard phase and a binder phase, and the hard phase is WC and WC.
B1 formed when a component other than WC is blended, which is formed by substituting 0 to 15% by weight of the above with carbides, nitrides, and carbonitrides of metals of Groups 4a, 5a, and 6a of the Periodic Table.
The mold solid solution phase is composed of a composite carbide solid solution or a composite carbonitride solid solution. The binder phase is mainly composed of an iron group metal such as Co and is contained in a proportion of 5 to 15% by weight in the total amount.

The cemented carbide base material used in the cutting tool of the present invention has a surface area near the surface of the cemented carbide base material having a minimum hardness of 90 to 98% as compared with the hardness inside the base material. Characterize. When the hardness in the vicinity of the surface of the base material is lower than 90% as compared with the hardness inside the base material, the hardness is remarkably lowered due to an increase in cutting temperature during processing of the difficult-to-cut material, causing compositional deformation of the cutting edge. On the other hand, if it exceeds 98%, the surface of the base material is too hard, so that when work-hardened stainless steel is cut, it cannot bear the impact and is broken. Therefore, the hardness near the surface must be set to 90 to 98% of the hardness inside the base material.

FIG. 1 shows the hardness gradient of the cemented carbide base material used in the cutting tool of the present invention and the conventional cemented carbide base material. Conventionally, the minimum hardness of the toughened surface layer in the de-beta layer by addition of nitride or nitrogen, which is known as a method of surface toughening of the cemented carbide base material, is about 50 compared to the hardness inside the base material.
It is -80%, and the cutting temperature remarkably rises in the cutting of the difficult-to-cut material, so that the composition is softened and the composition is deformed. On the other hand, since the cemented carbide base material used in the cutting tool of the present invention has toughened the surface without adding nitrogen, in the cutting temperature rising region in the cutting of difficult-to-cut materials, sufficient hardness for cutting is obtained. The toughness in the vicinity of the surface is increased while maintaining the same.

Further, in the cemented carbide base material used in the cutting tool of the present invention, as shown in the distribution of each metal element near the surface of FIG. 2, from the group consisting of groups 4a, 5a and 6a of the periodic table. The surface region toughened by having a region in which the ratio of Zr in the selected metal is higher in the vicinity of the surface of the cemented carbide base material than in the interior of the cemented carbide base material, further improves the strength at high temperatures, It can have excellent fracture resistance. The main reason for this is that Zr has excellent toughness and plastic deformation resistance at high temperatures. Further, in the above region, the amount of the binder phase is increased in correspondence with the decrease of most of the metals of groups 4a, 5a and 6a other than Zr in the periodic table. This increase in the amount of the binder phase contributes to the strengthening of the toughness, and, in relation to the wear resistance, the amount of the binder phase to be increased is 4th in the periodic table.
By incorporating a little amount of the metals of group a, 5a and 6a, the plastic deformation resistance is not adversely affected. Therefore,
The cutting tool of the present invention also has improved wear resistance due to the excellent plastic deformation resistance of Zr at high temperatures.

Further, as shown in FIG.
The thickness of the region where the ratio of Zr in the metal selected from the group consisting of a, 5a and 6a is higher than that of the inside of the cemented carbide base material is 5 to 100 μm from the surface of the base material toward the inside. Is preferred. This range is suitable because when the region where the Zr ratio is higher than the inside of the cemented carbide base material is 5 μm, the strength is insufficient and the plastic deformation and damage of the tool become severe, and when it exceeds 100 μm. This is because the wear resistance may decrease and the amount of tool wear may significantly increase.

In the cemented carbide base material, two or more kinds of B1 type solid solution phases exist inside the base material, and at least one of the B1 type solid solution phases is compared with other B1 type solid solution phases. The B1 type solid solution phase containing a large amount of Zr also provides excellent plastic deformation resistance at high temperatures and improves wear resistance. That is, the composition of the B1-type solid solution phase changes with the formation of the solid solution phase having a large Zr content, and the wettability with the binder phase is improved, so that the entire alloy is strengthened.
Proper presence of the type 1 solid solution phase maintains the mechanical strength at high temperatures, resulting in excellent cutting performance for high-speed and high-efficiency machining of difficult-to-cut materials.

In this case, the B1-type solid solution phase having a large Zr content is preferably present in the alloy as a phase having an average particle size of 3 μm or less. This is because when the average particle size exceeds 3 μm, the B1 type solid solution phase is poor in wetting with the binder phase, and the strength of the entire alloy decreases. Optimally, the average particle size is about 1 μm. That is, since the solid solution phase itself is inherently brittle, when precipitated as a coarse phase in the alloy, the mechanical strength is remarkably reduced, and when used as a cutting tool, the tool is severely damaged and plastically deformed. Therefore,
It is necessary that the average particle size of the B1 type solid solution phase having a large Zr content be within the above range.

Furthermore, according to the present invention, the content of Ta in the metals of Groups 4a, 5a and 6a of the Periodic Table in the total amount of the cemented carbide base material is 1% by weight or less in terms of TaC, especially 0.
Excellent wear resistance, plastic deformation resistance, and fracture resistance can be maintained even when the content is 2% by weight or less, and even when it is not substantially contained except as unavoidable impurities. That is, the Vickers hardness (Hv) is 1400 or more, the fracture toughness (K _1c ) is 12 mPa / m ^1/2 or more, and the three-point bending strength is 2500 MPa or more, without using a Ta material that is extremely expensive compared to other materials. Thermal conductivity 70W at 800 ℃
/ M · K or more, which is a cemented carbide base material having excellent thermal and mechanical properties.

The hard layer coated is TiC, TiN, T
Carbides, nitrides, carbonitrides, and TiAlNs of metals of groups 4a, 5a, and 6a of the Periodic Table including iCN,
TiZrN, TiCrN, or the like ZrO _2, Al ₂ O ₃ and the like, which by a CVD method or a PVD method 0.1-2
It is desirable to be formed to a thickness of 0 μm.

In order to manufacture the above cemented carbide base material, first, for example, 80 to 90% by weight of tungsten carbide powder having an average particle size of 0.5 to 10 μm and an average particle size of 0.5 to 10 μm are used in Periodic Table 4a. Iron having a total amount of 0.1 to 10% by weight of carbide, nitride and carbonitride powders of 5a and 6a group metals or solid solution powders of two or more of these metals, and an average particle size of 0.5 to 10 μm. The group metal is mixed in an amount of 5 to 15% by weight, and if desired, metal tungsten (W) powder or carbon black (C) is mixed.

Next, the powder mixture is molded into a predetermined shape by a known molding method such as press molding, cast molding, extrusion molding, cold isostatic pressing, etc.
In a vacuum of 15 Pa, the temperature is raised at 1 to 20 ° C./min, and 1350
The above-described cemented carbide base material can be obtained by firing at -1500 ° C for 0.2-5 hours, particularly 0.5-2 hours.

In order to obtain a cemented carbide base material having a surface area having a minimum hardness of 90 to 98% in the vicinity of the surface as compared with the hardness inside the base material, which is a feature of the present invention, a nitride is used as a primary raw material. And / or C to the carbides forming the so-called B1-type solid solution without adding carbonitrides
The amount of the binder phase metal such as o and the amount of C in the two-phase sound region in the cemented carbide base material are adjusted, and both the heating rate especially near the liquid phase appearance temperature and the cooling rate after the firing are set in the firing conditions. It is necessary to control about 5 ° C./min. Further, it can be obtained more efficiently by performing hydrogen flow in the degreasing process or firing in a decarburizing atmosphere.

Further, the primary raw material of the cemented carbide base material is adjusted by adjusting the addition ratio of the Zr compound to the carbides of the metals of the 4a, 5a and 6a groups of the periodic table constituting the B1 type solid solution and firing by the above method. As a result, it is possible to obtain a cemented carbide base material that retains wear resistance due to excellent strength and excellent plastic deformation resistance at high temperatures.

Here, the thickness of the surface region having the minimum hardness of 90 to 98% as compared with the hardness inside the cemented carbide base material can be controlled by adjusting the holding temperature and time during firing. is there.

Further, the cemented carbide base material used for the cutting tool of the present invention described above has excellent mechanical properties and thermal properties such as high hardness, high strength and high thermal conductivity. It can be applied to wear members, high-temperature structural materials, and the like, and can be suitably used as a cutting tool, and further as a cutting tool for difficult-to-cut materials such as stainless steel.

Further, the cutting tool of the present invention is characterized in that, on the surface of the above-mentioned cemented carbide base material, carbides, nitrides, carbonitrides, TiAlN, TiZr of metals of groups 4a, 5a and 6a of the periodic table are provided.
A single layer or a plurality of layers of at least one kind of coating layer selected from the group consisting of N, TiCrN, diamond and Al ₂ O ₃ may be formed.

In order to form a coating layer on the cemented carbide base material, after polishing or cleaning the surface of the cemented carbide base material, if desired, a conventionally known thin film forming method such as PVD method or CVD method. Can be used. The thickness of the coating layer is 0.1 to 20 μm.
It is desirable that it is m.

[0031]

EXAMPLE A tungsten carbide (WC) powder having an average particle size of 8.0 μm, a metal cobalt (Co) powder having an average particle size of 1.2 μm, and a compound powder shown in Table 1 having an average particle size of 2.0 μm are shown in Table 1. After adding at a ratio shown in Table 1 and mixing, and after molding into a cutting tool shape (SDK42, CNMG43) by press molding, from a temperature lower than the firing temperature by 500 ° C or more to 10 ° C /
The temperature was raised at a rate of minutes and the mixture was fired at 1500 ° C. for 1 hour to produce a cemented carbide base material.

On a cut surface cut in an oblique cross-sectional direction including an arbitrary surface, a load of 200 g is held inward from the surface by a micro-Vickers device (MVK-G3) manufactured by Akashi Co., at a portion corresponding to each depth from the surface. The hardness was measured for 10 seconds. The hardness was measured at at least three points at each depth and the average value was taken to determine the hardness at that depth. Further, the hardness at a depth of at least 1000 μm was measured and used as the internal hardness of the cemented carbide base material.

Further, the content ratio of each metal component in the solid solution phase inside the cemented carbide base material is analyzed by energy dispersive X-ray analysis (E
DS), which gives the periodic table 4a, 5
A region in which the ratio of Zr in the metal selected from the group consisting of a and 6a was higher than that in the inside of the cemented carbide base material was specified.

As for the B1 type solid solution phase containing a large amount of Zr, a sample whose ground surface was mirror-finished was observed in an arbitrary region (20 μm) in SEM electron microscope (backscattered electron image) observation.
× 20 μm) B1 type solid solution (gray)
The precipitation of solid solutions having different colors can be discriminated, and the average particle size of the B1 type solid solution phase having a large Zr content was measured by the Luzex image analysis method. The results are shown in Table 1.

The "minimum hardness ratio (%)" in Table 1 is the ratio of the minimum hardness of the surface area of the cemented carbide base material to the hardness of the inner base material part (minimum hardness of the surface area / hardness inside the base material). Indicates. In addition, “Zr / β increasing region” in Table 1 is the periodic table 4a, 5a,
A region in which the ratio of Zr in the metal selected from the group consisting of 6a group is higher than that in the inside of the base metal is indicated by a circle, which means that the region exists, and a mark by which the x symbol does not exist. . The “thickness (μm)” of the “Zr / β increasing region” is the thickness of the region where the ratio of Zr in the metal selected from the group consisting of groups 4a, 5a and 6a of the periodic table is higher than that in the base metal. is there. Further, "Zr-containing β phase" in Table 1 means a B1 type solid solution phase having a large Zr content, and a mark "○" indicates that the region exists and a mark "X" indicates that the region does not exist.
The "particle size (μm)" of the "Zr-containing β phase" indicates the particle size of the B1 type solid solution containing a large amount of Zr.

[0036]

[Table 1]

On the surface of each of the obtained cemented carbide base materials,
A TiN film having a film thickness of 2 μm was formed by a PVD method to manufacture a cutting tool.

Using this cutting tool, a stainless steel turning process was carried out for 15 minutes as a wear test under the following conditions to measure the flank wear amount and boundary damage amount of the cutting tool. When the flank wear amount reached 0.2 mm or the boundary damage amount reached 0.5 mm during the cutting test, the cutting time was measured. Further, as a toughness test, milling of a grooved alloy steel was carried out to measure the feed when a defect occurred. The results are shown in Table 2. Wear test Work material: Stainless steel (SUS304) Tool shape: CNMG432 Cutting speed: 120 m / min Feed speed: 0.3 mm / rev Cutting depth: 2 mm Others: Water-soluble cutting fluid toughness test Work material: Grooved alloy steel ( SCM440H) Tool shape: SDK42 Cutting speed: 80 m / min Feed speed: Variable 0.2 to 0.8 mm / Blade cut: 2 mm Others: Dry cutting

[0039]

[Table 2]

From the results shown in Tables 1 and 2, the sample No. 1 having a low minimum hardness in the surface region with respect to the inside of the base material was used. Nos. 8 and 9 had poor wear resistance. Also, sample N with a minimum hardness of 88%
o. No. 10 had a problem in fracture resistance. Furthermore, hardness 1
10%, the hardness of the surface area is higher than that of the inside of the base material. No. 11 had a problem of boundary damage and was inferior in fracture resistance.

On the other hand, according to the present invention, the sample N in which the minimum hardness of the surface region relative to the inside of the base material is 90 to 98%
o. For each of 1 to 7, the flank wear amount is 0.2 m
When the thickness was m or less, there was no problem with boundary damage, and excellent abrasion resistance was exhibited. In addition, the feed that causes a fracture in the toughness test was 0.5 mm / flute or more, which was practically sufficient, and had excellent fracture resistance.

These have a region where the ratio of Zr in the metal selected from the group consisting of groups 4a, 5a and 6a of the periodic table is higher than that in the base metal and a B1 type solid solution phase having a high Zr content. It is also effectively obtained.

Sample No. As shown in Nos. 1, 4 and 7, even if TaC, which has been used to improve the high temperature characteristics of the cemented carbide base material, is hardly added, it is an excellent ultra-fine alloy having a good balance of wear resistance and fracture resistance. A hard alloy base material could be obtained.

[0044]

As described in detail above, according to the cemented carbide base material used for the cutting tool of the present invention, the hardness of the cemented carbide base material in the vicinity of the surface of the cemented carbide base material is 90 to 98% as compared with the hardness inside the base material. Since it has a surface area with the minimum hardness of, it can combine the hardness and toughness of the cemented carbide base material, and by using this as a cutting tool, even for the cutting of difficult-to-cut materials such as stainless steel It is possible to obtain a cutting tool having excellent wear resistance, plastic deformation resistance, and fracture resistance, and capable of highly efficient cutting.

[Brief description of drawings]

FIG. 1 is a diagram showing a hardness gradient inside a base material of a cemented carbide base material used in a cutting tool of the present invention and a conventional cemented carbide base material.

FIG. 2 is a diagram showing an element distribution inside a cemented carbide base material used in the cutting tool of the present invention.

Claims (6)

[Claims] 1. A periodic table 4a containing at least WC,
A cemented carbide matrix comprising one or more hard phase components of carbides, nitrides and / or carbonitrides of metals selected from the group consisting of 5a and 6a and one or more binder phase components of iron group metals. In the cutting tool having a coating layer on the surface of the base material, the hardness of the base material near the surface of the cemented carbide base material is 90 to 90% as compared with the hardness inside the base material.
A cutting tool having a surface area having a minimum hardness of 98%. 2. A metal selected from the group consisting of groups 4a, 5a and 6a of the periodic table, containing Zr as a metal selected from the group consisting of groups 4a, 5a and 6a of the periodic table. The cutting tool according to claim 1, wherein a region in which the ratio of Zr in the base metal is higher than that in the inside of the cemented carbide base material is near the surface of the cemented carbide base material. 3. The cutting tool according to claim 2, wherein the thickness of a region where the Zr ratio is higher than the inside of the cemented carbide base material is 5 to 100 μm. 4. Two or more kinds of B are provided inside the cemented carbide base material.
There is a type 1 solid solution phase, and one of the B1 type solid solution phases is present.
The seed is a B1 type solid solution phase having a higher Zr content than the other B1 type solid solution phases.
Alternatively, the cutting tool according to claim 3. 5. The cutting tool according to claim 4, wherein the B1 type solid solution phase containing a large amount of Zr has an average particle diameter of 3 μm or less. 6. The content of Ta in the metal selected from the group consisting of groups 4a, 5a and 6a of the periodic table is Ta.
The cutting tool according to any one of claims 1 to 5, which is 1% by weight or less of the total amount in terms of C.