KR101816712B1 - Cutting tools having hard coated layer - Google Patents

Abstract

The present invention relates to a cutting tool having a hard coating film with excellent adhesion with a cemented carbide preform and excellent abrasion resistance. According to the present invention, the cutting tool is a cutting tool including a cermet preform, and a hard coating film formed of a single layer or multi-layer structure formed on a surface of the cermet preform. The preform includes a core-rim structure, and a core structure in the core-rim structure is distributed within 10 points in a scanning electron microscope image area which is an observed area of the preform at a 5000 magnifications. A binder phase deficiency layer is formed in at least a depth of 5m from the surface of the preform in which a content of the deficiency layer in a metal bind phase is less than or equal to 0.5 wt%. The hard coating film comprises Ti.

Description

TECHNICAL FIELD [0001] The present invention relates to a cutting tool having a hard coating,

More particularly, the present invention relates to a cutting tool having a hard coating formed on a surface of a Ti-based cermet having a core including a hard phase and a rim structure surrounding the core, The present invention relates to a cutting tool capable of improving the toughness and abrasion resistance of a base material made of a Ti based thermometer and improving the adhesion strength with a hard coating formed on a Ti based cermet so as to obtain an improved tool life .

WC-Co cemented carbide, Ti-based sintered alloy of Ti (C, N) type, cermet, other ceramics or high-speed steel are used as the base material of the wear resistant tool or cutting tool used for cutting the metal.

Of these, WC-Co cemented carbide is mainly composed of cobalt and tungsten, which have strong strategic material characteristics, and thus has a high price.

Cermet generally refers to a composite composed of a ceramic hard phase and a metal bond phase. In particular, in the field of cutting tools, a hard ceramic such as WC, NbC, TaC, or Mo ₂ C, based on TiC or Ti And a binder phase powder mainly composed of a metal such as nickel (Ni), cobalt (Co) and / or iron (Fe) are mixed and then sintered in a vacuum or hydrogen atmosphere or an argon atmosphere to form a ceramic- Composite sintered body.

Cermet has been attracting attention as a substitute for WC-Co cemented carbide because of its high hardness, chemical stability at high temperature, low specific gravity and low cost of raw material. , And WC-Co-based cemented carbide are relatively limited in toughness.

For example, when a cermet is manufactured using TiC, a binding metal such as nickel (Ni), cobalt (Co) and / or iron (Fe) is used in sintering. In this case, There is a problem that the toughness of the TiC particles is increased and the toughness is lowered.

The problem of the cermet using TiC is that TiC is thermodynamically more stable and TiC (C, N) having a fine structure is formed by adding TiN to TiC to obtain an increase in toughness to some extent.

On the other hand, in the microstructure of a conventional TiC-based or Ti (C, N) -saminated sintered body, a solid solution containing a core existing as TiC or Ti (C, N) and another carbide added around the core a core-rim structure is formed in which a rim consisting of a solid-solution: (Ti, M1, M2) (C, N) is formed. As described above, the rim structure surrounding the core is a structure having higher toughness than TiC or Ti (C, N) constituting the core, and thus can improve the toughness of the cermet.

However, due to the existence of cores inducing brittleness in the centrifugal structure, there is a limit in replacing the WC-Co cemented carbide because the toughness is lower than that of the WC-Co cemented carbide.

In order to solve the brittleness problem of the cermet, as described in the following Patent Literature, carbides, carbonitrides, or mixtures thereof of two or more metals selected from metals of Groups 4, 5, and 6 of Periodic Table including titanium A method of obtaining a sintered body having no centrifugal structure by using a hard phase powder composed of a completely solid phase with no freezing structure is proposed.

In this method, finer grain size and sintering temperature are reduced by limiting the particle size of the solid phase powder not having a core structure to 200 nm or less as a starting material. When mass production of at least 100 kg or more, , There is a problem that mass production is difficult because the powder is aggregated and easily oxidized. Furthermore, in this method, the metal phase is contained in an amount of about 20% by weight in order to obtain a high fracture toughness while limiting the particle size of the solid solution powder to 200 nm or less. When the content of the metal bond phase is kept as high as 20% Hardness and abrasion resistance are difficult to obtain.

On the other hand, a cermet or a cemented carbide used as a cutting tool is used after forming a hard coat layer on its surface in order to increase abrasion resistance. The hard coat is formed by chemical vapor deposition (CVD) or physical vapor deposition (PVD) do.

The cutting edge of the cutting tool is exposed to a high temperature environment of about 1000 캜 during high speed machining of a high hardness material and not only abrasion due to contact with the workpiece and abrasion due to oxidation but also mechanical shock such as interruption is received. Therefore, cutting tools require properties such as adequate oxidation resistance, abrasion resistance and resistance to chipping.

For this purpose, the hard coating for a cutting tool is generally composed of a single layer or a multilayer non-oxide thin film, an oxide thin film having excellent oxidation resistance, or a mixed layer thereof. Examples of the non-oxide thin film include TiN, TiC, Ti the periodic table group 4, and a carbide, nitride, carbonitride of a Group 5, Group 6 metals, examples of the oxide-based thin film, such as (CN) has a typically α-Al ₂ O _3.

Such a hard coating film is advantageous in improving the peeling resistance and improving the tool life as the bonding property with the base material is improved.

For this purpose, a hard coating having good bonding properties to a base material such as a TiN layer is formed on a base material of a conventional tool, or a hard coating such as Ti (CN) and? -Al ₂ O ₃ is formed on the TiN layer The adhesion of the hard coating may not be sufficient by merely forming the hard coating having good bonding property.

1. Korean Patent Publication No. 2004-0009859 2. Korean Patent Publication No. 2007-0099056 3. Korean Patent Publication No. 2005-0038163 4. Korean Patent Publication No. 2005-0032533 5. Korean Patent Publication No. 2007-0017564 6. Korean Patent Publication No. 1993-0010710

An object of the present invention is to provide a cutting tool in which a hard coating is formed on the surface of a base material made of a Ti-based thermoplastic material, the toughness of the base material, the abrasion resistance, and the peel resistance of the hard coating are improved.

According to an aspect of the present invention, there is provided a cutting tool comprising a cermet base material and a hard coating formed on the surface of the base material, the base material having a core-rim structure, The core structure of the rim structure is distributed within 10 points of the scanning electron microscope image area observed at a magnification of 5,000 times, and the binder phase having a metal binding phase content of 0.5 wt% or less from the surface of the base material, Wherein the hard coating is formed of a hard coating, and the hard coating comprises Ti.

The cutting tool according to the present invention can improve the toughness of the base material by minimizing the area fraction of the cores in the core-rim structure which is a cause of brittleness of the Ti-based cermet tool and to remove the metal bond phase from the surface portion of the base material to a predetermined thickness A binder phase depletion layer is formed to improve abrasion resistance, and a component of a hard film is diffused into the binder phase depletion layer to form a mixed structure, thereby achieving an improved tool life.

1 is a scanning electron microscope image showing a Ti-based cermet structure in which the area fraction of the core is minimized according to Example 3 of the present invention.
2 is a scanning electron microscope image showing a Ti-based cermet structure manufactured according to Comparative Example 1. Fig.
Fig. 3 is a compositional profile of Ti, W, Ni and Co measured from the surface of a Ti-based cermet prepared according to Example 3 of the present invention to a thickness of 30 mu m.
Fig. 4 is a composition profile of Ti, W, Ni and Co measured from the surface of a Ti-based cermet prepared according to Comparative Example 1 to a thickness of 25 mu m.

The singular forms used to describe the embodiments of the present invention are meant to include plural forms unless the phrases expressly mean the opposite. And includes meaning of specific characteristics, regions, integers, steps, and actions. Elements and / or components, and other particular features, regions, integers, steps, acts. Quot; does not exclude the presence or addition of elements, elements and / or groups.

Although not defined differently, all terms including technical terms and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention belongs. Also, commonly used predefined terms are not to be construed as ideal or very formal meanings unless further defined and interpreted as having a meaning consistent with the relevant technical literature and the present disclosure.

The inventors of the present invention have studied a method for improving the tear resistance of a hard coating while improving the toughness and abrasion resistance of a cutting tool in which a hard coating is formed on a Ti-based cermet as a base material. As a result, In the core-rim structure formed on the base material, the ratio of the area of the hard phase constituting the core is minimized to improve the toughness of the entire base material. The decrease in hardness, The metal bond layer is removed from the surface to a predetermined depth to form a bond layer depletion layer and the hard coating formed on the base material of the Ti-based cermet is diffused in the bonding layer depletion layer, and then the hard coating is post- State, and at the same time improving the bonding force of the hard coating to the base material, it is possible to improve the toughness, abrasion resistance, Revealing that can improve both the releasable led to the present invention.

The cutting tool according to the present invention includes a cermet base material and a hard coating formed on the surface of the base material, the base coating having a single-layer or multi-layer structure, wherein the base material includes a core- The tissue is distributed within 10 points of the scanning electron microscope image area observed at a magnification of 5,000 times, and a binder-phase depletion layer having a metal binding phase content of 0.5 wt% or less is formed from the surface of the base material to at least a depth of 5 mu m And the hard coating contains Ti.

The cermet base material may include a hard phase containing a Ti compound and a W compound, and a metal bond phase selected from Co, Ni, Co, and Ni. The Ti compound may include Ti carbide and / or Ti carbonitride, and the W compound may include W carbide and / or carbonitride.

The cermet base material preferably contains 40 to 94% by weight of a carbonitride containing Ti, 5 to 20% by weight of at least one metal selected from Fe, Co and Ni, Group 4, Group 5 and Group 5 of the periodic table, 1 to 40% by weight of a carbide, a carbonitride, or a mixture thereof, containing at least one metal selected from Group 6 metals.

If the content of the metal-bonded phase in the base material is less than 5% by weight, the brittleness increases. When the base metal content exceeds 20% by weight, the abrasion resistance is reduced, so that the content of the metal-bonded phase is preferably 5 to 20% by weight. If the content of the carbide or carbonitride containing the element of Group 4, Group 5 or Group 6 is less than 1% by weight, the abrasion resistance required for the cutting tool according to the present invention can not be obtained. If the content is more than 40% The occurrence of heat cracks due to repetitive thermal shocks increases, so that it is preferably added in an amount of 40 wt% or less.

In addition, when the base material is distributed over 10 points in the scanning electron microscope image area observed at a magnification of 5000 times, the hard core structure is not preferable because the toughness of the base material is not sufficient.

In addition, the component of the hard coating containing Ti may preferably be diffused into the bonding-phase depletion layer to form a mixed structure of the hard coating and the base metal.

The bonding-phase depletion layer may be formed by a method of dissolving and removing the metal bonding layer formed to a predetermined thickness from the surface of the base material by etching the surface of the Ti-based cermet. However, And there is no particular limitation so long as it is a method capable of forming a thickness as described in the present invention.

If the depth from the surface is less than 5 mu m, it is difficult to obtain a sufficient bonding force with the hard coating and the base material, and it is difficult to obtain the abrasion resistance. When the depth from the surface is less than 50 mu m The impact resistance is lowered. The depth of the bond-phase depletion layer is preferably 8 to 20 占 퐉, in consideration of wear resistance and impact resistance.

In addition, in the hard coating, various coatings such as TiN, Ti (C, N), and Al ₂ O ₃ may be formed on the surface of the base material in accordance with the characteristics required for the cutting tool However, considering the chemical affinity with the Ti compound, which is a hard phase constituting the Ti-based cermet, the TiN layer is preferable, and the TiN layer formed diffuses into the bonding-deficient layer formed on the surface of the base material, To form a mixed structure of Ti compound TiN. The thus formed mixed structure improves the peel resistance of the TiN layer and improves the abrasion resistance of the cutting tool.

[Example]

The cermet according to the embodiment of the present invention was produced through the following process.

First, raw powder for sintering was prepared so as to have the composition shown in Table 1 below.

ingredient
(weight%) (Ti, W) (C, N)
content
(weight%) Ti
compound WC Ta Mo Nb Co Ni Comparative Example 1 50 18 One 6 9 8 8 0 Comparative Example 2 40 18 One 6 9 8 8 10 Comparative Example 3 35 18 One 6 9 8 8 15 Example 1 30 18 One 6 9 8 8 20 Example 2 20 18 One 6 9 8 8 30 Example 3 10 18 One 6 9 8 8 40

The content of (Ti, W) (C, N) in the table indicates the weight ratio of (Ti, W) (C, N) in the weight of the entire raw material powder, (Ti, W) (C, N) is Ti (C, N).

A cemented carbide ball and an organic solvent were added to the raw material powder, followed by mixing and grinding for 17 hours to obtain a mixed powder. The obtained mixed powder was pressed at a pressure of 2 ton / cm 2 through a shape metal mold of CCMT09T304 Posi type to prepare a molded article.

Next, a first dewaxing process was performed at 450 ° C and a second dewaxing process was performed at 650 ° C to 750 ° C using an inert gas. After removing the organic binder component introduced in the molding process, the sintering was conducted at 1500 ° C for 1.5 hours, cooled at a rate of 8.5 ° C / min in a hydrogen gas atmosphere from 1500 ° C to 1100 ° C, Sintering process was performed to fabricate inserts made of Ti-based thermoset.

Fig. 1 is a scanning electron microscope image showing a Ti-based cermet structure in which the area fraction of the core is minimized according to Example 3 of the present invention, Fig. 2 is a scanning electron microscope image showing a Ti-based cermet structure produced according to Comparative Example 1, It is a microscopic image.

As shown in FIG. 1, among the microstructures of the inserts prepared according to Example 3 of the present invention, it can be seen that core structures appearing relatively black on the image are observed at less than 10 points in the image of 5000 times magnification, The same is true for the embodiment. If the core structure is not so large, the toughness of the insert is improved.

Also in the case of Examples 1 and 2, the core texture was observed to be less than 10 points as in Example 3. [

FIG. 2 shows the microstructure of the insert prepared according to Comparative Example 1. As shown in FIG. 2, in Comparative Example 1, the black core is uniformly dispersed. When the core structure develops like this, the toughness of the insert is not good.

In the case of Comparative Examples 2 and 3, the number of core tissues was decreased as compared with Comparative Example 1, but was observed to exceed 10 points.

The thus-prepared insert is immersed in an acidic solution (electrolytic degreasing agent, Korea Synthesizer SR100) to selectively dissolve Co and Ni, which are metal bonding phases, to form a 'bond phase depletion layer '.

The depth of the 'bond-phase depletion layer' may vary depending on the contact time with the acid solution, and Table 2 below shows depths of the 'bond-depletion layer' formed according to Examples 1 to 3 and Comparative Examples 1 to 3.

The distance (um) from the top surface to the point where the binder content is at least 0.5 wt% Comparative Example 1 0 Comparative Example 2 2 Comparative Example 3 4 Example 1 5 Example 2 5.5 Example 3 7

As shown in Table 1, in the case of Comparative Example 1, the step of immersion in an acidic solution was not performed. In Comparative Example 2 and Comparative Example 3, the depth of the 'bonding-phase depletion layer' was less than 5 μm, ~ 3 so that the depth of the 'binding-depletion layer' was 5 μm or more.

Fig. 3 is a composition profile of Ti, W, Ni and Co measured from the surface of a Ti-based cermet prepared according to Example 3 of the present invention to a thickness of 30 mu m.

As shown in FIG. 3, in the case of the Ti-based cermet prepared according to Example 1 of the present invention after immersion in an acidic solution, the content of Co and Ni, which are metallic bonding phases of up to about 7 탆 in thickness, And the ratio of the binder phase gradually increases. From the point of about 30 탆 in thickness, it can be seen that the content of the metal binding phase is expressed by the ratio of the raw material powder.

On the other hand, as shown in FIG. 4, in the case of Comparative Example 1 not immersed in an acidic solution, a " bonding top layer " in which the content of Co and Ni is greater than about 2 to 3 m from the surface portion of the base material And the content of the binder phase gradually increases from the point of 5 mu m after the metal content is gradually decreased.

Thus, a TiN layer having a thickness of 2.0 占 퐉 was formed on the surfaces of the inserts prepared according to Examples 1 to 3 and Comparative Examples 1 to 3 by CVD.

When the TiN layer is formed as described above, a portion of the TiN layer diffuses from the surface of the base of the insert into the 'coupling-phase depletion layer' of the cermet base material, ). ≪ / RTI > On the other hand, the diffusion of the TiN layer may be performed in the process of forming the hard coating, and if the diffusion is not sufficient, the diffusion layer may be formed through a separate heat treatment.

The cutting tool thus manufactured was first evaluated for wear resistance and chipping resistance before the acidic solution immersion treatment and the TiN layer formation treatment, and after the acidic solution immersion treatment and the TiN layer were formed, the abrasion resistance and the TiN layer The adhesion was evaluated.

The abrasion resistance, the chipping resistance and the adhesion of the TiN layer were evaluated under the following conditions.

(1) Condition for evaluating abrasion resistance

Feed rate = 350 mm / min, feed = 0.2 mm / rev, infeed amount: 1.0 mm (one side)

Conducted the outer diameter machining of S45C carbon steel

(2) Evaluation conditions for chipping resistance

Feed rate: 200 mm / min, feed = 0.25 mm / rev, infeed amount: 1.0 mm (one side)

S45C-Execution of machining of interrupted workpiece with 4 grooves

(3) Adhesion evaluation condition

And evaluated according to the ASTM C1624 method using a scratch test equipment of JNL.

      At this time, the moving distance of the scratch pressure particle was 10.0 mm and the feeding condition was 1.0 mm / sec.

Table 3 below shows the results of evaluating the wear resistance and the chipping resistance in the state before the acidic solution immersion treatment and the TiN layer formation treatment.

Base material without TiN layer formation Abrasion resistance evaluation
(minute)
VB wear time to 0.2 mm Evaluation of chipping resistance
(minute) Comparative Example 1 11 5 Comparative Example 2 10 6 Comparative Example 3 8.5 8 Example 1 7 15 Example 2 8.2 14 Example 3 5 20

The time indicated in the evaluation of the wear resistance is based on the arrival time of 0.2 mm of abrasion wear VB wear. In case of chipping resistance, it is time to break.

As shown in Table 3, in Comparative Examples 1 to 3, as the content of (Ti, W) (C, N) increases, the chipping resistance (i.e., toughness) is improved but the abrasion resistance is decreased.

Table 4 below shows the results of evaluating the abrasion resistance and the degree of adhesion in the state after the acidic solution immersion treatment and the TiN layer formation treatment are carried out in Examples 1 to 3 and Comparative Examples 2 and 3.

TiN layer
thickness
(um) Coherence
(KN) Evaluation of tool life and adhesion after TiN formation Abrasion resistance
(minute) Chipping resistance
(minute) Comparative Example 1 2.0 88 KN 15 13 Comparative Example 2 2.0 93 KN 24 14 Comparative Example 3 2.0 99 KN 32 18 Example 1 2.0 120 KN 68 24 Example 2 2.0 116 KN 74 31 Example 3 2.0 119 KN 91 44

As shown in Table 4, Example 1 of the present invention exhibited remarkably improved wear resistance and adhesion as compared with Comparative Examples 2 and 3, and Comparative Examples 1 to 3 in which acidic solution immersion treatment was not performed in Examples 1 to 3 It can be seen that remarkable improvement is achieved in terms of abrasion resistance and adhesion.

On the other hand, the adhesion of the TiN layer shows substantially similar levels in Examples 1 to 3, so that it can be seen that the thickness of the bonding-phase-depletion layer is similar to the thickness of 5 mu m or more.

When the degree of adhesion is improved as in the embodiment of the present invention, the bonding force between the base material and the thin film is excellent, and the resistance to external impact increases, so that the chipping resistance is improved from a tool standpoint.

In addition, due to the peeling occurring at the cutting edge due to the cutting load during the high speed machining, the cutting load is concentrated in the peeled area, so that the time for reaching the VB wear of 0.2 mm is reduced by the excessive load. The peeling resistance is excellent and the tool life can be prolonged.

Claims (6)

1. A cutting tool comprising a cermet base material and a hard coating formed on the surface of the base material,
Wherein the base material comprises a core-rim structure,
The core structure of the core-rim structure is distributed within 10 points of the scanning electron microscope image area observed at a magnification of 5,000 times,
A binder phase depletion layer having a metal binding phase content of 0.5 wt% or less from the surface of the base material to at least a depth of 5 mu m is formed,
Wherein the hard coating comprises Ti,
Wherein a hard coating film containing the Ti is diffused into the bonding-phase depletion layer to form a mixed structure of the hard coating and the base metal. The method according to claim 1,
The cermet,
A hard phase containing a Ti compound and a W compound,
Co, Ni or a metal bond phase selected from Co and Ni. delete The method according to claim 1,
Wherein the binder phase depletion layer is formed to a depth of 5 to 50 mu m from the surface. The method according to claim 1,
Wherein the hard coating is a TiN layer formed on the surface of the base material. The method according to claim 1,
The cermet base material,
40 to 94% by weight of a carbonitride containing Ti, 5 to 20% by weight of at least one metal selected from Fe, Co and Ni, at least one metal selected from Group 4, Group 5 and Group 6 metals in the periodic table, 1 to 40% by weight of a carbide, carbonitride, or a mixture thereof.

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