KR102584679B1 - Cemented carbide for cutting tools and method for manufacturing the same - Google Patents

Abstract

The present invention relates to a cemented carbide for cutting tools containing 4 to 13% by weight of Co, 1 to 12% of a compound and the balance of WC and other inevitable impurities, wherein the average particle diameter of the compound is 0.4 ㎛ or less, When the average particle diameter of the WC is 1.2 to 2.2㎛, the average particle diameter of the compound and the average particle diameter of the WC satisfy the following relational equation 1.
[Relationship 1]
18 ≤ 100(A/B) ≤ 30
(In the above relational equation 1, A refers to the average particle diameter of the compound in cemented carbide for cutting tools, and B refers to the average particle diameter of WC)

Description

Cemented carbide for cutting tools and method for manufacturing the same}

The present invention relates to a cemented carbide for cutting tools, preferably a cutting tool with improved resistance to plastic deformation and resistance to crater wear by controlling the average particle diameter of WC and the average particle diameter of the compound of the cemented carbide to an appropriate level. It relates to cemented carbide alloy and its manufacturing method.

Cemented carbide refers to an alloy manufactured by mixing hard tungsten carbide (WC) particles with a bonding phase provided by Co, Ni, and Fe. The cemented carbide alloy has high hardness and strong toughness, so it is used as tool steel for cutting tools for processing metals or high-strength ceramics.

Typically, in order to improve the mechanical properties of cemented carbide alloy, methods are mainly used to change the composition of the cemented carbide alloy or to diversify the microstructure. As a representative example, Republic of Korea Patent No. 10-1792534 discloses a method of strengthening hardness through controlling the microstructure of WC and composition of the hard coating layer, and Republic of Korea Patent No. 10-2050644 discloses the composition of Ti and "CFL". A method of improving wear resistance and impact resistance is disclosed by controlling the thickness of the layer of the Cubic phase Free Layer (Cubic phase Free Layer) to an appropriate range. In addition, Republic of Korea Patent No. 10-1302374 discloses that the content of carbides excluding WC is set to a predetermined range. A method for limiting is disclosed.

However, in addition to the above methods, there is a constant need for a method of manufacturing cemented carbide that can enhance mechanical properties by controlling sintering conditions.

Republic of Korea Patent No. 10-1792534 (2017.10.26.) Republic of Korea Patent No. 10-2050644 (2019.11.25.) Republic of Korea Patent No. 10-1302374 (2013.08.27.)

In order to solve the above problems, the present invention controls the sintering temperature and cooling rate to control the average particle diameter of cemented carbide to an appropriate range, thereby improving resistance to plastic deformation and crater wear for cutting tools. Cemented carbide alloy and its manufacturing method can be provided.

One embodiment of the present invention for achieving the above object is a cemented carbide for cutting tools containing 4 to 13% by weight of Co, 1 to 12% of the compound and the balance of WC and other inevitable impurities, wherein the compound When the average particle diameter of is 0.4㎛ or less and the average particle diameter of the WC is 1.2 to 2.2㎛, the average particle diameter of the compound and the average particle diameter of the WC satisfy the following relational equation 1. It is about cemented carbide for tools.

[Relationship 1]

18 ≤ 100(A/B) ≤ 30

(In the above relational equation 1, A refers to the average particle diameter of the compound in cemented carbide for cutting tools, and B refers to the average particle diameter of WC)

In one embodiment, the compound may be provided as a carbide, nitride, or carbonitride formed by combining one or more elements selected from the group consisting of Group 4a, Group 5a, or Group 6a elements with carbon or nitrogen.

In one embodiment, the compound may be provided as a carbide in which one or more elements selected from the group consisting of Group 4a, Group 5a, or Group 6a elements are combined with carbon.

In one embodiment, the cemented carbide for cutting tools may have a crack point of 25% or less.

[Relational Expression 2]

Crack point A= (number of interfaces of compounds per unit area) / (total number of compounds per unit area) x 100

Another embodiment of the present invention relates to a cutting tool made of the cemented carbide for cutting tools described above and a hard film formed on the surface of the cemented carbide.

In one embodiment, the hard film may be formed by one or more methods selected from CVD (chemical vapor deposition) and PVD (physical vapor deposition) methods.

Another embodiment of the present invention is a step of preparing a mixture by weighing and mixing raw material powder consisting of 4 to 13% by weight of Co, 1 to 12% of the compound and the balance of WC, and placing the mixture in a mold. It includes the steps of producing a molded body by pressing and sintering the mixture to produce cemented carbide, wherein the sintering step includes degreasing the molded body at about 200 to 300° C. for 1 to 3 hours, and the degreased molded body. Primary sintering at 1,000 to 1,250°C, secondary sintering of the primary sintered body at 1,400 to 1,450°C, tertiary sintering of the secondary sintered body at 1,500 to 1,600°C, tertiary sintering It relates to a method of manufacturing cemented carbide for cutting tools, comprising the steps of primary cooling the molded body to 1000 to 1300°C and secondary cooling the primary cooled molded body to room temperature.

In one embodiment, the secondary sintering may be performed for 90 to 120 minutes.

In one embodiment, the secondary cooling may be performed at a cooling rate of 120 to 150°C/min.

Above, in the cemented carbide for cutting tools according to an embodiment of the present invention, when the average particle diameter of the compound is 0.4㎛ or less and the average particle diameter of the WC is 1.2 to 2.2㎛, the average particle diameter of the compound and the WC By controlling the average particle diameter to an appropriate level, resistance to plastic deformation and resistance to crater wear can be improved.

Through this, the wear resistance of the cutting tool can be improved and its lifespan can be increased.

1 is a flowchart for explaining a method of sintering cemented carbide for cutting tools according to an embodiment of the present invention.
Figure 2 is a photograph of a cross-section of cemented carbide for cutting tools manufactured according to Example 1 of the present invention.
Figure 3 is a photograph of a cross-section of cemented carbide for cutting tools manufactured according to Comparative Example 1 of the present invention.
Figure 4 is a photograph for measuring crack points according to an embodiment of the present invention.
Figure 5 is a photograph of the amount of plastic deformation of the cutting tool manufactured according to Example 1 of the present invention.
Figure 6 is a photograph of the amount of plastic deformation of the cutting tool manufactured according to Comparative Example 1 of the present invention.
Figure 7 is a photograph of the crater wear width manufactured according to Example 1 of the present invention.
Figure 8 is a photograph of the crater wear width manufactured according to Comparative Example 1 of the present invention.

Hereinafter, the cemented carbide for cutting tools according to the present invention will be described in detail. The drawings introduced below are provided as examples so that the idea of the present invention can be sufficiently conveyed to those skilled in the art. Accordingly, the present invention is not limited to the drawings presented below and may be embodied in other forms, and the drawings presented below may be exaggerated to clarify the spirit of the present invention. At this time, if there is no other definition in the technical and scientific terms used, they have meanings commonly understood by those skilled in the art to which this invention pertains, and the gist of the present invention is summarized in the following description and attached drawings. Descriptions of known functions and configurations that may unnecessarily obscure are omitted.

According to one feature of the present invention, the present invention provides a cemented carbide alloy for cutting tools with excellent resistance to plastic deformation and crater wear resistance, including 4 to 13% of Co, 1 to 12% of the compound and the balance of WC and other inevitable impurities. It's about.

In this specification, WC refers to tungsten carbide formed by combining tungsten (W) powder and carbon (C) powder.

As used herein, the compound may refer to carbides, nitrides, and carbonitrides formed by combining one or more elements selected from the group consisting of Group 4a, Group 5a, or Group 6a elements with carbon or nitrogen.

For example, the compounds are carbides, nitrides, and carbonitrides formed by combining one or more metals selected from the group consisting of Cr, Zr, Nb, Mo, Ti, Hf, Ta, and V with 1% by weight or less of C or N. It can mean. More preferably, the compound may be provided as a metal carbide in which one or more metals selected from the group consisting of Cr, Zr, Nb, Mo, Ti, Hf, Ta and V and 1% by weight or less of carbon are combined. More preferably, it may be provided as any one metal carbide selected from TiC, NbC, and TaC.

Hereinafter, for convenience of explanation, in this specification, the compound is considered to be a carbide in which one or more metals selected from the group consisting of Cr, Zr, Nb, Mo, Ti, Hf, Ta and V and 1% by weight or less of carbon are combined. Although it is explained by way of example, it is not limited to this, and it is obvious that the same can be applied to nitride and carbonitride.

According to an embodiment, the present invention can control the particle diameter of the compound and the WC by controlling the temperature increase rate and cooling rate during the manufacturing process.

For example, the present invention includes the steps of degreasing a molded body mixed with raw material powder at about 200 to 300°C for 1 to 3 hours, and maintaining the degreased molded body for a certain time at 1,000 to 1,250°C. A step of secondary sintering of the first sintered molded body at 1,400 to 1,450°C for a certain period of time, a third sintering of the secondly sintered body at 1,500 to 1,600°C for a certain period of time, tertiary sintering. The cemented carbide for cutting tools can be manufactured by performing the steps of first cooling the molded body to 1000 to 1300°C and secondary cooling the first cooled molded body to room temperature.

In this process, in the third sintering step, 1,500 to 1,600°C is maintained for 90 to 120 minutes, and in the second cooling step, the temperature is cooled at a cooling rate of 120 to 150°C/min to reduce the particle diameters of the compound and the WC. It can be adjusted.

As a result, the average particle diameter of the compound and the average particle diameter of the WC can be controlled to satisfy the following relational equation 1.

[Relationship 1]

18 ≤ 100(A/B) ≤ 30

(In the above relational equation 1, A refers to the average particle diameter of the compound in cemented carbide for cutting tools, and B refers to the average particle diameter of WC)

In addition, in the cemented carbide for cutting tools, the average particle diameter of the compound can be controlled to 0.4 ㎛ or less, and the average particle diameter of the WC can be controlled to 1.2 to 2.2 ㎛.

In other words, the present invention can be manufactured with an average particle diameter of the compound of 0.4 ㎛ or less and an average particle diameter of the WC of 1.2 to 2.2 ㎛ by controlling the sintering time and cooling rate during the manufacturing process, While the average particle diameter of the compound and the WC is provided in the above-mentioned range, resistance to plastic deformation and crater wear can be secured by additionally limiting the ratio of the average particle diameter of the compound and the WC.

According to an embodiment, if the ratio (A/B) between the average particle diameter of the compound and the average particle diameter of the WC is less than 18, it means that the particles of the compound are too fine than the WC particles.

Typically, the compound may be dissolved between the lattices formed by the Co bond phase in the cemented carbide to form an interstitial solid solution. The compound contained in the interstitial solid solution form can induce solid solution strengthening by interfering with the movement of dislocations in the cemented carbide alloy. As a result, the mechanical properties of the cemented carbide alloy can be improved.

However, in this process, if the particle size of the compound is too small, the interstitial solid solution cannot effectively impede the movement of dislocations, making it difficult to induce a sufficient solid solution strengthening effect. As a result, the mechanical strength of the cemented carbide may be reduced, which means that the wear resistance and chipping resistance of the cemented carbide are reduced. This means that when a cutting tool is manufactured from the cemented carbide alloy, the resistance to plastic deformation of the cutting tool is reduced, so that deformation easily occurs and crater wear can easily occur.

Conversely, if the ratio (A/B) of the average particle diameter of the compound and the average particle diameter of the WC exceeds 30, it means that a coarse-sized compound was formed. In this case, one compound may combine with one or more other compounds formed around it to form a single coarse compound. This can also reduce the resistance to plastic deformation and crater wear resistance of the cemented carbide alloy by lowering the density of the compound.

That is, the present invention can produce cemented carbide for cutting tools with excellent resistance to plastic deformation and crater wear resistance by controlling the sintering time and cooling rate by controlling the cemented carbide alloy to achieve the most optimal solid solution strengthening effect. Comparison results of plastic deformation resistance and crater wear resistance according to the sintering time and cooling rate will be described later.

Above, the cemented carbide alloy for cutting tools according to an embodiment of the present invention has been described. In this specification, cemented carbide for cutting tools has been described, but it goes without saying that cutting tools manufactured from the cemented carbide for cutting tools can also be applied in the same way.

According to an embodiment, the cutting tool may further include the cemented carbide and hard film for cutting tools described above.

According to an embodiment, the hard film is a film including one or more alumina layers and may be formed on the surface of the base material formed of the cemented carbide alloy.

For example, the hard film may include a TiC _x N _y O _z (x+y+z=1) layer having a single-layer or multi-layer structure between the base material made of cemented carbide and the alumina layer. In addition, the Ti(C,N,O) layer contains additive elements such as aluminum (Al), zirconium (Zr), and boron (B), and the alumina layer and the TiC _x N _y O _z (x+y +z=1) The bonding characteristics of the layer can be improved.

According to an embodiment, the hard film may be formed through one or more methods selected from CVD (chemical vapor deposition) or PVD (physical vapor deposition).

Hereinafter, the manufacturing method of the cemented carbide alloy for cutting tools will be described with reference to FIG. 1.

1 is a flowchart for explaining a method of sintering cemented carbide for cutting tools according to an embodiment of the present invention.

The method for producing cemented carbide for cutting tools according to an embodiment of the present invention is to prepare a mixture by weighing and mixing raw material powder consisting of 4 to 13% Co, 1 to 12% compound and the balance WC in weight percent. It may include the steps of putting the mixture into a mold and pressurizing it to produce a molded body, and sintering the mixture to produce cemented carbide.

First, Co powder, compound powder, and WC powder can be prepared. At this time, the compound powder refers to a powder composed of carbides, nitrides, and carbonitrides containing one or more elements selected from the group consisting of group 4a, group 5a, or group 6a elements.

The powder was weighed to have 4 to 13% by weight of Co, 1 to 12% by weight of compound, and the balance of WC, and then mixed to prepare a mixture. At this time, in order to mix the powder uniformly, the mixer can be operated at 40 to 60 rpm for primary mixing, and then after primary mixing, the powder can be operated at 5 to 15 rpm for secondary mixing.

Afterwards, the mixture was pressed to produce a molded body, and the molded body was sintered to produce cemented carbide for cutting tools.

Referring to Figure 1, according to the embodiment, the sintering step includes a) degreasing the molded body at about 200 to 300°C for 1 to 3 hours, b) first sintering the degreased molded body at 1,000 to 1,250°C. c) secondly sintering the first sintered molded body at 1,400 to 1,450°C, d) thirdly sintering the secondarily sintered molded body at 1,500 to 1,600°C, e) thirdly sintered the thirdly sintered molded body at 1,000 to 1,000°C. It may include primary cooling to 1300°C and f) secondary cooling of the primary cooled molded body to room temperature.

Step a) is a process of removing unnecessary impurities in the sintering process by dewaxing the molded body at about 200 to 300° C. for 1 to 3 hours.

According to the embodiment, the degreasing step may be performed by any one degreasing method selected from heat degreasing, solvent degreasing, and catalytic degreasing.

Afterwards, the degreased molded body can be first sintered through step b) by maintaining the temperature at 1,000 to 1,250°C for 30 to 120 minutes.

Afterwards, the degreased molded body can be subjected to secondary sintering through step c) by maintaining the temperature at 1,400 to 1,450°C for 30 to 120 minutes.

Predetermined rigidity can be imparted to the molded body through the primary sintering and secondary sintering.

Afterwards, the secondary sintered molded body can be thirdly sintered at 1,500 to 1,600°C for 90 to 120 minutes through step d) to remove pores formed in the molded body and improve strength.

According to an embodiment, if the third sintering time is less than 90 minutes, the amount of carbide diffusing into Co may be reduced because the particles do not receive sufficient heat energy to grow during the sintering process. This may result in a decrease in the number of compound particles per unit area in the cemented carbide alloy and a relative decrease in the average particle diameter of the compound particles. On the other hand, if the third sintering time exceeds 120 minutes, the WC and the compound may overgrow and the average particle diameter may increase. For this reason, the third sintering time is preferably 90 to 120 minutes, and more preferably 90 to 100 minutes.

After the first to third sintering, the thirdly sintered molded body through step e) may be first cooled to 1000 to 1300°C. At this time, the primary cooling may be performed at a cooling rate of 1 to 10°C/min.

Finally, through step f), the primary cooled molded body can be secondary cooled to room temperature (25°C).

According to an embodiment, the primary cooling may be performed slowly at a cooling rate of 1 to 10°C/min, while the secondary cooling may be rapid cooling at a cooling rate of 120 to 150°C/min.

If the secondary cooling is performed at less than 120°C/min, the time required to completely cool to room temperature increases, resulting in an increase in the average particle diameter of the compound. This means that, as explained above, one compound can combine with one or more other compounds formed around it to form a single coarse compound. For this reason, the wear resistance and resistance to plastic deformation of the cemented carbide alloy can be reduced.

Conversely, if the secondary cooling exceeds 150°C/min, the average particle diameter of the compound may be excessively reduced. As explained earlier, this also causes a decrease in the wear resistance and resistance to plastic deformation of cemented carbide alloy.

Additionally, residual stress may occur inside the cemented carbide alloy due to excessive rapid cooling. In this case, cracks or breaks may occur in some cemented carbide alloys, which may reduce the yield of the product. For this reason, the secondary cooling is preferably performed at 120 to 150°C/min, and more preferably at 120 to 130°C/min.

Hereinafter, the cemented carbide for cutting tools according to the present invention will be described in more detail through examples. However, the following examples are only a reference for explaining the present invention in detail, and the present invention is not limited thereto, and may be implemented in various forms.

Additionally, unless otherwise defined, all technical and scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention pertains. The terminology used in the description herein is merely to effectively describe particular embodiments and is not intended to limit the invention. Additionally, the unit of compounds not specifically described in the specification may be weight percent.

[Example 1]

Co powder, NbC powder (hereinafter referred to as compound), and WC powder were prepared. Afterwards, the metal powder was weighed to contain 8.3 wt% of Co, 4 wt% of NbC, and residual WC, and then first mixed at 40 rpm using a mixer, followed by second mixing at 5 rpm to prepare a mixture. Afterwards, the prepared mixture was placed in a mold and pressed to produce a molded body.

The manufactured molded body was degreased at 250°C for 120 minutes, and then first sintered at 1200°C for 30 minutes. The first sintered molded body was immediately subjected to second sintering at 1,430°C for 60 minutes, and after the second sintering, third sintering was performed at 1,550°C for 90 minutes. All of the first to third sinterings were performed in an Ar atmosphere.

The molded body that completed the third sintering was then first cooled from 1500°C to 1200°C at a cooling rate of 5°C/min, and after stabilizing the sintered alloy, it was secondarily cooled from 1200°C to 25°C at a cooling rate of 120°C/min. Cemented carbide for cutting tools was manufactured by cooling.

[Example 2]

All processes were performed in the same manner as in Example 1 except that the third sintering was performed for 120 minutes.

[Example 3]

All processes were performed in the same manner as in Example 1 except that secondary cooling was performed at a cooling rate of 150°C/min.

[Comparative Example 1]

All processes were performed in the same manner as in Example 1 except that the third sintering was performed for 150 minutes.

[Comparative Example 2]

All processes were performed in the same manner as in Example 1 except that the third sintering was performed for 60 minutes.

[Comparative Example 3]

All processes were performed in the same manner as in Example 1 except that secondary cooling was performed at a cooling rate of 60°C/min.

[Comparative Example 4]

All processes were performed in the same manner as in Example 1 except that secondary cooling was performed at a cooling rate of 180°C/min.

Examples 1 to 3 and Comparative Examples 1 to 4 are summarized in Table 1 below.

Third sintering time (min) Secondary cooling rate (℃/min) Example 1 90 120 Example 2 120 120 Example 3 90 150 Comparative Example 1 150 120 Comparative Example 2 60 120 Comparative Example 3 90 60 Comparative Example 4 90 180

[Analysis and Performance Evaluation]

1) Microstructure analysis of cemented carbide alloy:

The cross-sections of the cemented carbide for cutting tools manufactured in Examples 1 to 3 and Comparative Examples 1 to 4 were mirror polished and the microstructure was observed using an optical microscope.

Figure 2 is a photograph of a cross-section of cemented carbide for cutting tools manufactured according to Example 1 of the present invention, and Figure 3 is a photograph of a cross-section of cemented carbide for cutting tools manufactured according to Comparative Example 1 of the present invention.

Referring to Figure 2, it can be seen that the cemented carbide alloy manufactured according to Example 1 contains a compound provided as NbC in the WC base material mixed in an appropriate size. Additionally, it can be confirmed that two or more compounds do not combine to form an interface and are separated from each other.

On the other hand, referring to Figure 3, it can be seen that in the cemented carbide alloy manufactured according to Comparative Example 1, the compounds were not mixed evenly during the mixing process, and some compounds were combined with each other to form an interface. That is, it can be seen that the density of the cemented carbide manufactured according to Comparative Example 1 was reduced compared to the cemented carbide alloy prepared according to Example 1.

2 and 3, the cemented carbide manufactured according to Example 1 has an excellent solid solution strengthening effect due to the compound compared to the cemented carbide manufactured according to Comparative Example 1, and as a result, the wear resistance of the cemented carbide is improved. can be expected to happen.

The average atomic diameter of the WC and the compound on this microstructure was quantitatively measured using an image analyzer, and the ratio between the average particle diameter of the compound and the average particle diameter of the WC was calculated based on the measured atomic diameter. At this time, the ratio of the average particle diameter of the compound and the average particle diameter of the WC was calculated according to the following relational equation 1.

[Relationship 1]

18 ≤ 100(A/B) ≤ 30

(In the above relational equation 1, A refers to the average particle diameter of the compound in cemented carbide for cutting tools, and B refers to the average particle diameter of WC)

Above, the average particle diameter of the WC, the average particle diameter of the compound, and the ratio of the average particle diameter of the compound and the average particle diameter of the WC are shown in Table 2 below.

Average particle diameter (㎛) NbC/WC
(A/B) WC(A) NbC (B) Example 1 1.59 0.36 22.64% Example 2 2.02 0.39 19.31% Example 3 1.71 0.37 21.64% Comparative Example 1 1.76 0.55 31.25% Comparative Example 2 2.33 0.39 16.74% Comparative Example 3 1.71 0.57 33.33% Comparative Example 4 2.45 0.44 17.96%

Referring to Table 2, Examples 1 to 3 are the average particle diameter of the compound and the WC, with the average particle diameter of the compound satisfying 0.4 ㎛ or less and the average particle diameter of the WC satisfying 1.2 to 2.2 ㎛. It can be seen that the average particle diameter was formed in a range that satisfies the above relational equation 1.

On the other hand, in Comparative Example 1, the sintering time was increased to 150 min during the third sintering, and as a result, the average diameter of the compound increased to 0.55 ㎛ relative to Example 3, which had a similar WC average particle diameter. As a result, it was confirmed that the ratio (A/B) of the average particle diameter of the compound and the average particle diameter of the WC exceeded 30%.

In Comparative Example 2, the sintering time was reduced to 60 min during the third sintering, and as a result, the average particle diameter of the compound decreased relative to the average particle diameter of WC. As a result, it can be confirmed that the ratio (A/B) of the average particle diameter of the compound and the average particle diameter of the WC is less than 18%.

In Comparative Example 3, the cooling rate during secondary cooling was reduced to 60°C/min, and as a result, the average particle diameter of the compound increased relative to the average particle diameter of WC. As a result, it was confirmed that the ratio (A/B) of the average particle diameter of the compound and the average particle diameter of the WC exceeded 30%.

In Comparative Example 2, as the cooling rate was increased to 180°C/min during secondary cooling, the average particle diameter of the compound decreased relative to the average particle diameter of WC. As a result, it can be confirmed that the ratio (A/B) of the average particle diameter of the compound and the average particle diameter of the WC is less than 18%.

That is, in the cemented carbide for cutting tools according to an embodiment of the present invention, the secondary sintering is performed for 90 to 120 minutes in the above-described manufacturing process, and the secondary cooling is performed at a cooling rate of 120 to 150 ° C./min. The ratio (A/B) of the average particle diameter of the compound and the average particle diameter of the WC may be 18 to 30%.

2) Measurement of resistance to plastic deformation and crater wear resistance:

A crack point comparison test and an abrasion resistance test were performed to compare the resistance to plastic deformation and crater wear resistance of the cemented carbide manufactured according to Examples 1 to 3 and Comparative Examples 1 to 4.

2-1) Crack point comparison experiment

In the present invention, a crack point refers to a point where cracks easily occur. Typically, cracks tend to occur at the interface between compounds and grow along the interface, causing destruction. For this reason, if the number of interfaces between compounds is small compared to the total number of compounds, the occurrence of cracks can be suppressed and mechanical strength can be improved. As a result, plastic deformation and crater wear of cemented carbide and cutting tools made from the cemented carbide can be prevented.

Hereinafter, the crack point is a crack point A, which means the interface ratio of the compound among all compounds formed in a unit area, and the unit area is divided into 20 equal areas and subdivided into small areas, and the average of the interface ratio of the compound formed in each area. It can be divided into crack point B. The crack point A and crack point B can be defined as follows.

Crack point A = (number of interfaces of compounds per unit area) / (total number of compounds per unit area)

Crack point B = ²{(number of interfaces of compounds in each region) / (total number of compounds in each region)

In order to compare the crack point A and crack point B, the cross-section of the cemented carbide manufactured according to Examples 1 to 3 and Comparative Examples 1 to 4 was mirror polished, and then an area of 5 x 4 ㎟ was photographed with an optical microscope, and the area The crack point was calculated by measuring the total number of compounds observed and the number of interfaces between the compounds.

In addition, as shown in Figure 4, when 5

Number of interfaces in compounds Total number of compounds Crack Point A Crack Point B Example 1 72 394 18.27% 17.94% Example 2 85 382 22.25% 21.22% Example 3 76 410 18.54% 17.62% Comparative Example 1 190 699 27.18% 27.08% Comparative Example 2 129 494 26.11% 26.09% Comparative Example 3 210 734 28.61% 28.48% Comparative Example 4 134 501 26.75% 26.42%

Referring to Table 3, it can be seen that the cemented carbide alloys manufactured according to Examples 1 to 3 had crack point A of 18.27, 22.25, and 18.54%, respectively, which is 25% or less. This can prevent the formation of cracks by adjusting the number of interfaces to an appropriate level compared to the total number of compounds, and improve resistance to plastic deformation.

Crack point B was also measured at 17.94, 21.22, and 17.62%, confirming that the compound was formed evenly without overproducing it in a specific area.

On the other hand, it can be observed that the crack point of the cemented carbide manufactured according to Comparative Examples 1 to 4 exceeds 25%.

Specifically, in Comparative Examples 1 and 3, the average particle diameter of the chemical increased, resulting in a relatively increased number of interfaces between the compounds, and as a result, the crack point exceeded 25%.

In Comparative Examples 2 and 4, the average particle diameter was reduced, but the total number of compounds was relatively reduced, and as a result, the crack point exceeded 25%. However, the reason why the number of compounds decreased in Comparative Examples 2 and 3 was because the standard for measuring the number of compounds was to measure compounds that can be distinguished by an optical microscope, that is, compounds with a minimum diameter that can be distinguished by an optical microscope of 0.1㎛ or more. Although the number appears to have decreased, it is desirable to determine that many compounds were actually formed with a minimum particle size of less than 0.1㎛.

In order to verify the wear resistance effect according to the crack point A and crack point B, a wear resistance evaluation was performed under the following conditions, and the results are shown in Table 4.

Cutting conditions for wear resistance evaluation

- Work material: SCM 440

- Material size: Ψ300

- Processing type: Outer diameter

- Cutting speed: 260 m/min.

- Feed (feed): 0.45 mm/rev

- Cutting depth: 2.0 mm

- Dry cutting evaluation: Plastic deformation (PD) measurement after 6 minutes of cutting

NbC/WC
(A/B) Crack Point A Crack Point B Plastic deformation amount Example 1 22.64% 18.27% 17.94% 1.16㎜ Example 2 19.31% 22.25% 21.22% 1.18㎜ Example 3 21.64% 18.54% 17.62% 1.16㎜ Comparative Example 1 31.25% 27.18% 27.08% 2.25㎜ Comparative Example 2 16.74% 26.11% 26.09% 1.97㎜ Comparative Example 3 33.33% 28.61% 28.48% 2.16㎜ Comparative Example 4 17.96% 26.75% 26.42% 2.05㎜

Referring to Table 4, in Examples 1 to 3, where the actual crack point A and crack point B were both 25% or less, the plastic deformation was relatively reduced, and in comparison, the crack point A and crack point B were both greater than 25%. In Examples 1 to 4, the amount of plastic deformation increased. Through this, it can be seen that wear resistance is improved when the crack point is 25% or less.

In fact, comparing Figures 5 and 6, a photograph of the amount of plastic deformation of the cutting tool manufactured according to Example 1 (Figure 5) and a photograph of the amount of plastic deformation of the cutting tool manufactured according to Comparative Example 1 (Figure 6) ), it can be seen that the cutting tool manufactured according to Comparative Example 1 has a greater degree of plastic deformation than the cutting tool manufactured according to Example 1.

In addition, comparing Figures 7 and 8, it can be seen that the crater wear width of the cutting tool manufactured according to Example 1 (Figure 7) is narrower than the crater wear width of the cutting tool manufactured according to Comparative Example 1 (Figure 8). You can check it.

That is, the present invention experimentally confirmed that resistance to plastic deformation and crater wear resistance were improved by mixing the compound and the WC at an appropriate diameter size, and as a result, crack point and actual wear resistance were improved.

As described above, the present invention can provide a cemented carbide for cutting tools containing 4 to 13% by weight of Co, 1 to 12% of the compound, and the balance of WC and other inevitable impurities.

At this time, the compound may be provided as a carbide, nitride, or carbonitride formed by combining one or more elements selected from the group consisting of group 4a, group 5a, or group 6a elements with carbon or nitrogen.

According to an embodiment, the present invention controls the secondary sintering time and secondary cooling temperature in the step of manufacturing the cemented carbide alloy so that the average particle diameter of the compound is 0.4 ㎛ or less and the average particle diameter of the WC is 1.2 to 2.2 ㎛. It can be controlled with .

More preferably, in the cemented carbide alloy, the average particle diameter of the compound satisfies 0.4㎛ or less and the average particle diameter of the WC satisfies 1.2 to 2.2㎛, and the average particle diameter of the compound and the average particle diameter of the WC are as follows. The secondary sintering time and secondary cooling temperature of the cemented carbide alloy can be controlled to satisfy Relation 1.

[Relationship 1]

18 ≤ 100(A/B) ≤ 30

(In the above relational equation 1, A refers to the average particle diameter of the compound in cemented carbide for cutting tools, and B refers to the average particle diameter of WC)

Through this, the present invention can greatly improve resistance to plastic deformation and crater wear resistance.

Although the present invention has been described through specific details and limited examples as described above, these are provided only to facilitate a more general understanding of the present invention, and the present invention is not limited to the above-mentioned examples, and the present invention belongs to Those skilled in the art can make various modifications and variations from this description.

Accordingly, the spirit of the present invention should not be limited to the described embodiments, and the claims described below as well as all modifications that are equivalent or equivalent to the claims will fall within the scope of the present invention.

Claims (11)

In weight percent, carbides, nitrides and carbonitrides formed by combining 4 to 13% of Co, 1 to 12% of group 4a, group 5a or group 6a elements with carbon or nitrogen, and In the cemented carbide for cutting tools containing the remainder of WC and other inevitable impurities,
The average particle diameter of carbides, nitrides and carbonitrides formed by combining one or more elements selected from the group consisting of group 4a, 5a or 6a elements with carbon or nitrogen is 0.4㎛ or less, and the average particle diameter of the WC is 1.2 to 2.2㎛,
The average particle diameter of carbides, nitrides, and carbonitrides formed by combining one or more elements selected from the group consisting of group 4a, 5a, or 6a elements with carbon or nitrogen and the average particle diameter of the WC are expressed by the following relational equation 1: Cemented carbide for cutting tools, characterized in that it is satisfactory.
[Relationship 1]
18 ≤ 100(A/B) ≤ 30
(In the above equation 1, A is the average particle of carbide, nitride, and carbonitride formed by combining one or more elements selected from the group consisting of group 4a, group 5a, or group 6a elements with carbon or nitrogen in cemented carbide for cutting tools. means diameter, and B means the average particle diameter of WC)
delete delete According to paragraph 1,
The carbides, nitrides, and carbonitrides formed by combining one or more elements selected from the group consisting of group 4a, group 5a, or group 6a elements with carbon or nitrogen are characterized in that they are any one metal carbide selected from TiC, NbC, and TaC. Cemented carbide alloy for cutting tools.
According to paragraph 1,
The cemented carbide alloy for cutting tools is characterized in that the crack point A below is 25% or less.
Crack point A = (number of interfaces of compounds per unit area) / (total number of compounds per unit area)
A cutting tool manufactured using the cemented carbide for cutting tools according to any one of claims 1, 4, and 5.
According to clause 6,
The cutting tool further includes a hard film formed by one or more methods selected from CVD (chemical vapor deposition) and PVD (physical vapor deposition) methods.
In weight percent, carbides, nitrides and carbonitrides formed by combining 4 to 13% of Co, 1 to 12% of group 4a, group 5a or group 6a elements with carbon or nitrogen, and Preparing a mixture by weighing and mixing the remaining raw material powder consisting of WC;
Putting the mixture into a mold and pressurizing it to produce a molded body; and
It includes the step of producing cemented carbide alloy by sintering the mixture,
The sintering step is,
Degreasing the molded body at 200 to 300° C. for 1 to 3 hours;
Primary sintering of the degreased molded body at 1,000 to 1,250°C for a certain period of time;
Secondary sintering of the primary sintered molded body at 1,400 to 1,450°C for a certain period of time;
Thirdly sintering the secondary sintered molded body at 1,500 to 1,600°C for 90 to 120 minutes;
Primary cooling the thirdly sintered molded body to 1000 to 1300°C; and
A method for manufacturing cemented carbide for cutting tools, comprising: secondary cooling the primary cooled molded body to room temperature at a cooling rate of 120 to 150° C./min.
According to clause 8,
The first sintering step is maintained at 1,000 to 1,250°C for 30 to 120 minutes,
A method of manufacturing cemented carbide for cutting tools, characterized in that the secondary sintering step is maintained at 1,400 to 1,450°C for 30 to 120 minutes.
delete delete