WO2020111658A1 - Cutting insert for difficult-to-cut materials - Google Patents

Abstract

The present invention relates to a PVD ceramic thin film coated cutting insert that can be suitably used for processing difficult-to-cut materials having low thermal conductivity, such as Inconel and titanium. The cutting insert according to the present invention comprises: a cemented carbide base material having an SMS value of 50-80% obtained by following [Equation 1], wherein, when any part of the cemented carbide base material is observed at 20,000X magnification with a scanning electron microscope, the area of a Co structure in which an area of 1.5 ㎛ × 1.5 ㎛ (width × length) of the Co structure enters is 10% or less of the total area of the Co structure; and a ceramic thin film having a thickness of 0.4-1.5 ㎛ formed on the cemented carbide base material. [Equation 1] SMS = saturation magnetization value of a sintered body × 100/TMS (TMS = mass ratio of 2010 × Co)

Description

Cutting insert for difficult materials

The present invention relates to a PVD ceramic thin film coating cutting insert that can be suitably used for the processing of difficult-to-reduce materials such as Inconel or titanium.

As a base material for abrasion-resistant tools or cutting tools used for cutting metal, cemented carbide (WC-Co alloy), TiC or Ti(C,N), etc. are mainly used as hard materials, and Co, Ni, and Fe are used as binders. Cermet, other ceramics or high-speed steels are used.

Among them, cemented carbide is a composite material in which hard tungsten carbide (WC) particles are dispersed in a binder metal such as cobalt (Co), nickel (Ni), or iron (Fe), which has excellent toughness. It is widely used as a base material. In order to improve the mechanical properties such as wear resistance, toughness and high temperature characteristics of the base material for cutting tools, a grain growth inhibitory substance such as vanadium carbide (VC) is added to obtain a microstructure, or to reduce the concentration of the binder metal on the surface of the sintered body. Microstructure control such as or hatching has been used a lot.

In accordance with ISO classification, Inconel, titanium (Ti) alloy, etc., which fall within the S region, are difficult to process materials with high hardness and tensile strength and low thermal conductivity. In general, in the machining of difficult-to-cut materials, a sharp cutting edge shape that improves cutting tool cutting is applied, and this configuration is a choice for minimizing the cutting edge in low-speed processing of weldable hard-cut materials with high hardness.

However, in the cutting process of a difficult-to-cut material having a very low thermal conductivity, it is very difficult to effectively prevent the destruction of the edge of the blade by welding because the machining heat is concentrated at the edge of the sharp cutting insert. For this reason, in general, a ceramic insert is coated on a cutting insert for machining a difficult-to-cut material to prevent heat-blocking effect, abrasion resistance, and adhesion with a cemented carbide base material during cutting.

On the other hand, after using the cutting insert coated with the ceramic material for the processing of the difficult-to-cut material, it can be seen that the damage to the edge of the blade is closely observed and the adhesion and rapid wear of the base material proceed while the tearing and breaking of the ceramic thin film occurs. . Therefore, in order to increase the life of the cutting insert for difficult-to-cut materials, it is important to be able to suppress tearing and chipping damage of the ceramic thin film generated during cutting.

A problem to be solved by the present invention is to provide a cutting insert capable of prolonging life by suppressing plastic deformation of a ceramic thin film generated at the edge of a cutting insert during machining of difficult-to-cut materials and suppressing adhesion of a base material.

As a means for solving the above problems, the present invention, when an arbitrary portion is observed 20,000 times using a scanning electron microscope, the area of the Co tissue in which an area of 1.5 μm×1.5 μm (horizontal×vertical) enters therein It is difficult to cut, comprising a cemented carbide base material having an SMS value of 50 to 80%, which is 10% or less of the total Co tissue area, and the thickness of 0.4 to 1.5 µm formed on the cemented carbide base material, with an SMS value of 50 to 80% obtained by the following [Formula 1]. Recycling cutting inserts are provided.

[Equation 1]

SMS = Saturation magnetization value of sintered body × 100/TMS

(TMS = 2010×Co mass ratio)

The cutting insert according to the present invention, through the combination of a cemented carbide base material having a microstructure controlled to improve plastic deformation and prevent adhesion, and a thin ceramic thin film with improved adhesion and hardness, are used for cutting inserts under high temperature and high pressure. By suppressing the damage of the ceramic thin film generated at the edge of the blade and the adhesion of the base material, it is possible to greatly improve the life of the cutting insert used in the machining of difficult-to-cut materials.

Figure 1 shows the state after the cutting test of the cutting insert according to the Examples and Comparative Examples of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the embodiments of the present invention exemplified below may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below. The embodiments of the present invention are provided to more fully describe the present invention to those skilled in the art.

In the processing of difficult-to-cut materials, fine plastic deformation occurs at the edge of the cutting insert under high temperature and high pressure, and the ceramic thin film is broken by the fine plastic deformation, which causes rapid welding in the exposed base material part, leading to large welding detachment. , Resulting in damage to the edges. In particular, the welding phenomenon between the base material and the work piece after the thin film of the incision is worn is a major cause of deteriorating the roughness and shortening the life of the cutting insert.

In the cutting insert according to the present invention, when an arbitrary portion is observed at 20,000 times using a scanning electron microscope, the area of the Co tissue in which an area of 1.5 μm×1.5 μm (horizontal×vertical) enters is the total Co tissue area. It is characterized in that it comprises a ceramic thin film having a thickness of less than 10%, the SMS value obtained by the following [Equation 1] of 50 to 80%, and a thickness of 0.4 to 1.5 μm formed on the cemented carbide base material.

[Equation 1]

SMS = Saturation magnetization value of sintered body × 100/TMS

(TMS = 2010×Co mass ratio)

The present invention, by using a cemented carbide having a SMS value of 50 to 80% as the base material, improves plastic deformation, suppresses the breakage of the ceramic thin film, and at the same time, the microstructure of Co constituting the base material is 1.5 μm×1.5 μm (horizontal× The area of the vertical structure) so that the area of the Co structure entering the interior was 10% or less of the total Co structure area was prevented from easily occurring even if the ceramic thin film was broken by deformation. In addition, the thickness of the ceramic thin film formed on the cemented carbide base material was formed thin. Through the combination of these various configurations, it is possible to greatly improve the life of the cutting insert for machining difficult-to-cut materials.

The cemented carbide base material includes carbides, carbonitrides, carbonitrides or mixtures of one or more metals selected from Group 4, 5, and 6 metals in the periodic table excluding Co 4 to 8% by weight and tungsten (W). The sum of the grain growth inhibitor and the rare earth element is 5% by weight or less, and may include the remaining WC and unavoidable impurities.

The Co acts as a binder to hold the main hard phase WC, and the toughness increases as the Co content increases and the toughness decreases as the content decreases. When the Co content is less than 4% by weight, the toughness of the base material is insufficient, and when the Co content exceeds 8% by weight, plastic deformation is lowered, so 4 to 8% by weight is preferable.

When the grain growth inhibitor exceeds 5% by weight, since the bonding force between the WC and the binder is lowered and cracks between the WC and the binder are easily generated due to the impact received from the outside, the tool life can be reduced, so the grain growth inhibitor is 5 It is preferable to contain it by weight% or less. In addition, when the content of the particle growth inhibitor is less than 0.1% by weight, the particle growth inhibitory effect may be reduced and the high temperature plastic deformation may be reduced, so it is more preferable to include 0.1% by weight or more. In addition, the cemented carbide may optionally include one or more rare earth elements to have a solid solution strengthening effect, in which case it is preferable that the sum of the grain growth inhibitor and the rare earth elements is 5% by weight or less. As the rare earth element, for example, ruthenium (Ru), gadolinium (Gd), rhenium (Re), or the like may be used.

The unavoidable impurities are impurities that are unintentionally incorporated in the raw material and the manufacturing process, and are set to be 0.1% by weight or less, preferably 0.01% by weight or less.

It is preferable that the base material of the cemented carbide does not substantially contain abnormal structures such as a delta (δ) phase and a free carbon phase that degrade mechanical properties.

The adhesion between the cemented carbide base material and the ceramic thin film is preferably maintained at least 75N with a scratch tester. If the degree of adhesion is more than the above range, the desired effect in the present invention can be achieved, so the upper limit is not particularly limited.

The hardness of the ceramic thin film is preferably 30 GPa or more in order to suppress microplastic deformation during cutting.

The ceramic thin film is Ti _1-ab Al _a Me _b N formed by PVD method (Me is at least one selected from Si, W, Nb, Mo, Ta, Hf, Zr, Y, 0.3≤a≤0.7, 0 ≤b≤0.1).

The cemented carbide used as a base material used in the cutting tool according to the embodiment of the present invention was manufactured through the following process, and cemented carbide according to various compositions and processes was prepared together with the base material according to the embodiment of the present invention.

To this end, first, a raw material powder for manufacturing a cemented carbide was prepared to have the composition shown in Table 1 below.

Carbide balls and an organic solvent were added to the raw material powder prepared as described above, followed by mixing and grinding for 13 hours to obtain a mixed powder. With the obtained mixed powder, a press was performed by pressing at a pressure of 2 ton/cm 2 with a mold of CNMA120408 (Korea Metallurgy).

Next, by performing a dewaxing process at 600°C, after removing the organic binder component introduced in the manufacturing process of the molded body, sintering is performed in an inert gas atmosphere under conditions of a sintering temperature of 1450°C and a sintering time of 1 to 2 hours, After cooling at a predetermined cooling rate in an inert gas atmosphere up to 600° C., a sintering process was performed by natural cooling.

turn	WC			Base material composition (% by weight)		A(㎛)	B (%)	SMS (%)	Thin film thickness (㎛)	Remark
	Particle size 4.5	Particle size 2.5	Granularity 1.0	Co	Cr 3 C 2
One	92.8			6	1.2	3.2	72%	62	0.6	Comparative example
2	42.8	50		6	1.2	2.4	63%	61	0.6	Comparative example
3		92.8		6	1.2	1.9	48%	62	0.7	Comparative example
4		70	22.8	6	1.2	1.4	9%	62	0.6	Example
5		22.8	70	6	1.2	1.1	3%	60	0.7	Example
6			92.8	6	1.2	0.7	One%	61	0.7	Example

In Table 1,'A(㎛)' means the maximum size in the inscribed diameter that can be inserted into the Co structure after sintering. 'B(%)' means the ratio of the area of the Co structure in which the area of 1.5 µm x 1.5 µm (horizontal × vertical) enters the interior of the Co structure in the Co structure after sintering. 'Particle size 4.5' means that the average particle size of the starting powder used in the production is 4.5 µm. 'Particle size 2.5' means that the average particle size of the starting powder used in the production is 2.5 µm. 'Particle size 1.0' means that the average particle size of the starting powder used in the preparation is 1.0 µm.

As shown in Table 1, through the control of the WC particle size, in the Co structure after sintering, the ratio of the area of the Co structure in which the area of 1.5 μm×1.5 μm (horizontal×vertical) enters the total Co tissue area Can be controlled. In the case of the comparative example (Psalm Nos. 1 to 3), the ratio is more than 48%, but in the case of the embodiment (Psalm Nos. 4 to 5), the ratio is less than 10%. That is, the microstructure of the cemented carbide according to the embodiment of the present invention was controlled in a state where there is almost no coarse Co structure in which an area of 1.5 μm×1.5 μm (horizontal×vertical) enters therein.

On the other hand, by maintaining the SMS of the cemented carbide 60 to 62%, the plastic deformation was maintained above a certain level, and abnormal tissues such as delta phase and free carbon were not identified.

On the surface of all 6 types of cemented carbide base materials prepared as described above, by using a commercialized PVD method as shown in Table 1, the thickness was controlled to be 0.6 to 0.7 μm, and Ti _0.46 Al _0.52 Si _0.02 N thin film was coated. And, the adhesion of the thin film was set to 95N.

Cutting performance evaluation

As described above, the wear resistance of the cutting insert formed with the ceramic thin film was evaluated under the following conditions, and the results are summarized in Table 2 below.

-Workpiece: Inconel 718, Φ100

-Vc (cutting speed): 50mm/min

-fn (feed speed): 0.25mm/rev

-ap (depth of cut): 2.0mm

-Dry/Wet: Wet

turn	Roughness after 4 minutes processing (Ra;㎛)	Remark
One	2.6	Comparative example
2	2.4	Comparative example
3	1.9	Comparative example
4	0.9	Example
5	0.8	Example
6	0.8	Example

As can be seen in FIG. 1, in the case of the cutting inserts according to Nos. 1 to No. 2, welding phenomena began to appear in the machining for about 2 minutes, and the welded portions became coarse in subsequent machining. In addition, in the cutting insert according to No. 3, a welding phenomenon began to appear in 3 minutes of machining, and in the subsequent machining, a welded portion also increased. Accordingly, the machining roughness of the cutting inserts according to Nos. 1 to No. 3 after 4 minutes of machining was 1.9 to 2.6 μm, indicating a poor condition.

On the other hand, in the cutting inserts according to the examples No. 4 to No. 6 of the present invention, welding was hardly observed even for 4 minutes of machining, and the machining roughness was also good at a level of 0.8 to 0.9 μm.

That is, it can be seen that the cutting insert according to the embodiment of the present invention can exhibit excellent cutting performance in machining difficult-to-cut materials such as Inconel.

The present invention was carried out by the Ministry of Trade, Industry and Energy of the Ministry of Trade, Industry and Energy and the Korea Institute of Industrial Technology Evaluation and Management, "Development of Coating Carbide/cBN/Ceramic Tool for High-Hardness Heat-resistant Alloy Processing" of the Future Growth Engine Project (Task No. 10067065) It was done.

Claims (6)

1. When an arbitrary portion was observed by 20,000 times using a scanning electron microscope, the area of the Co tissue in which an area of 1.5 µm x 1.5 µm (horizontal × vertical) entered was 10% or less of the total Co tissue area, and the following [ Cemented carbide base material having an SMS value of 50 to 80% obtained by Equation 1],

   Cutting insert for difficult-to-cut material comprising a ceramic thin film of 0.4 ~ 1.5㎛ thickness formed on the cemented carbide base material.

   [Equation 1]

   SMS = Saturation magnetization value of sintered body × 100/TMS

   (TMS = 2010×Co mass ratio)
2. According to claim 1,

   The cemented carbide base material is a carbide, carbonitride, carbonitride, or mixtures of one or more metals selected from Group 4, 5, and 6 metals in the periodic table excluding Co 4 ~ 8 wt%, tungsten (W) A cutting insert for a difficult-to-cut material, wherein the sum of the grain growth inhibitor and rare earth elements contained is 5% by weight or less, and the remaining WC and cemented carbide containing unavoidable impurities.
3. According to claim 1,

   The cemented carbide base material has no abnormal structure, such as delta or free carbon, cutting insert for difficult materials.
4. According to claim 1,

   The adhesiveness between the cemented carbide base material and the ceramic thin film is 75 N or more as a scratch tester, cutting insert for difficult materials.
5. According to claim 1,

   Hardness of the ceramic thin film is 30GPa or more, cutting insert for difficult materials.
6. According to claim 1,

   The ceramic thin film, Ti _1-ab Al _a Me _b N formed by PVD method (Me is at least one selected from Si, W, Nb, Mo, Ta, Hf, Zr, Y, 0.3≤a≤0.7, Cutting insert for difficult-to-cut material, consisting of one or more layers including 0≤b≤0.1).

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