KR101302374B1 - Cemented carbide having good wear resistance and chipping resistance - Google Patents

Abstract

The present invention relates to a cemented carbide that is excellent in abrasion resistance and can be suitably used in cutting tools for machining difficult-to-cut materials such as stainless steel, since it is possible to suppress particle detachment (ie chipping) due to welding with a workpiece during cutting.
The cemented carbide according to the present invention is WC: 70 to 95% by weight, Co: 5 to 12% by weight, group 5a carbide: 0.1 to 3.0% by weight, and carbides containing unavoidable impurities, particles of the 5a group cubic carbide in microstructure The size is less than 1.5㎛, the average particle size of WC is characterized in that 3.0 ~ 5.0㎛.

Description

Cemented carbide with excellent wear resistance and chipping resistance {CEMENTED CARBIDE HAVING GOOD WEAR RESISTANCE AND CHIPPING RESISTANCE}

The present invention relates to a cemented carbide that can be used for cutting tools, and more specifically, it has excellent abrasion resistance, and in particular, it is possible to minimize the occurrence of particle dropping (ie chipping) due to welding with a workpiece during cutting, such as stainless steel. It relates to a cemented carbide that can be suitably used for cutting tools for machining difficult-to-cut materials.

Since the development of cemented carbides based on tungsten carbide (WC) and cobalt (Co) by Shredder of Germany in 1929, various methods have been studied to have properties suitable for various fields, and tungsten carbide (WC) and Carbide alloys based on cobalt (Co) are widely used as cutting tools and wear-resistant materials.

Cutting tools are used for cutting materials such as iron and steel (carbon steel, alloy steel), and various methods of manufacturing cemented carbide used as a base material to provide wear resistance and toughness suitable for the characteristics of various types of workpieces to be processed. Has been developed.

On the other hand, in order to further improve the wear resistance and toughness of the cutting tool, a metal carbide, carbonitride, such as Ti or Al, is used on the surface of the cemented carbide used as a base material by using a CVD (Chemical Vapor Deposition) or PVD (Physical Vapor Deposition) method. , A coating cutting tool having a coating layer such as carbonitride, oxide, etc. is widely used, and research for improving the performance of a cutting tool through improving the properties of the coating layer has been focused.

However, the role of overcoming the impact and high temperature generated during the actual cutting operation is mainly performed by the base material portion of the cutting tool, and as a method of improving the physical properties of the cutting tool base material, the particle size control, additive type, and Methods such as content control or binder phase content control are known.

For example, in Korean Patent Publication No. 2006-0110811, WC and Co, Ni, or Fe-based binder phases and gamma phases have substantially no gamma phase, and have a binder-rich rich surface area and mean particles of gamma phases. Disclosed is a method of improving the plastic deformation resistance and toughness of a cutting tool base material by limiting the size to less than 1 μm.

In addition, in Korean Patent Publication No. 2007-0000358, WC, a binder phase, and a cubic carbide phase, and basically has a binder phase incubation surface area without a cubic carbide phase, 3 to 20 wt% cobalt, 0.1 to 20 The total content of vanadium in weight percent and 70 to 95 weight percent WC as the remainder, and the other vanadium and other cubic carbide formers of groups 4a and 5a are 1 to 20% by weight, the average of WC A particle size of less than 1.5 µm, and the base material structure is free of free graphite, and thus a cemented carbide base material is disclosed to prevent toughness reduction by a grain growth inhibitor such as vanadium or chromium added to have a submicron structure.

In addition, Korean Patent Publication No. 2008-0019571 includes WC, a binder phase, and a cubic phase and also has a binder-like hatching surface area essentially free of cubic phase, 3 to 20% by weight cobalt, 1 to 15% by weight. % Of vanadium, less than 1% by weight of titanium, other cubic forming elements of groups 4A and/or 5A except vanadium and titanium, and WC particles having an average sintered particle size of WC greater than 1.5 µm, 70 to 92% by weight, , By adding the total content of elements of the 4A and/or 5A group to be 1 to 15% by weight, a base material having improved heat cracking resistance along with toughness is disclosed.

However, all of the above three prior arts have a binder-enriched layer formed on the surface. In general, when cutting steel, a large amount of cubic carbide phase is formed to increase cutting performance, and a long chip generated during cutting of steel is discharged. In the process of hitting the upper surface of the insert, which is a cutting tool, there is a problem in that crater wear is easily caused by chemical wear due to high/high pressure friction on the upper surface of the insert. It is advantageous to suppress. However, when these cubic carbides are added, the brittleness is relatively increased due to the effect of inhibiting grain growth and increasing the distribution of the hard phase, so that resistance to impact (impact resistance) is often deteriorated. In order to compensate for this, the formation of a binder-enriched layer without a cubic phase is used to suppress a decrease in impact resistance.

On the other hand, stainless steel is classified as a difficult-to-cut material, unlike ordinary steel or alloy steel. When cutting stainless steel, the affinity between the cutting tool and the work material is excellent, so the so-called chipping, which is the falling off of stainless steel as a workpiece, is the main problem. Therefore, a base material having a minimized content of a cubic carbide phase having a weaker bonding strength with a bonding phase is more advantageous than tungsten carbide (WC). There are limits to its implementation.

An object of the present invention is to solve the problem of providing a cemented carbide that can be suitably used as a base material for cutting tools for machining difficult-to-cut materials such as stainless steel because of excellent wear resistance and chipping resistance.

The present inventors have researched to solve the problem of chipping caused by welding of a cutting tool to a workpiece when machining difficult-to-cut materials such as stainless steel, which is a problem of the above-mentioned prior art. As a result, carbides (hereinafter referred to as'cubic carbide phases') By limiting the content of) to a predetermined range, limiting the elements constituting the cubic carbide phase to group 5a on the periodic table, limiting the size of the formed cubic carbide phase particles to a predetermined range, and limiting the particle size of WC to a predetermined range, It has been found that superior chipping resistance can be realized compared to the prior art, leading to the present invention.

The present invention as a means for solving the above problems, WC: 70 ~ 95% by weight, Co: 5 ~ 12% by weight, Group 5a carbide: 0.1 ~ 3.0% by weight, and carbides containing unavoidable impurities, the microstructure of the A particle size of the 5a group cubic carbide is 1.5 µm or less, and the average particle size of WC is 3.0 to 5.0 µm.

The reasons for limiting the composition and microstructure characteristics of the cemented carbide as described above in the present invention are as follows.

If the content of WC in the starting raw material combination is less than 70% by weight, the hardness, which is the advantage of cemented carbide, is significantly lowered, and when it exceeds 95% by weight, toughness and heat resistance of cemented carbide are greatly reduced, so it is difficult to simultaneously improve cutting toughness and wear resistance. , It is preferable that the content is 70 to 95% by weight.

In addition, if the content of Co as the bonding phase is less than 5% by weight, it is difficult to obtain a dense sintered body due to a lack of a liquid volume ratio during liquid phase sintering. Since it causes, it is preferable to contain it in the range of 5 to 12% by weight.

In addition, in the present invention, a group 5a carbide is used as a particle growth inhibitor. In the present invention, a group 5a carbide means carbides of V, Nb, and Ta, and group 5a carbides are contained in a range of 0.1 to 3.0% by weight. Preferably, when added in an amount of less than 0.1% by weight, that is, when the cubic carbide phase is hardly added, the difficult-to-reduce material has low thermal conductivity, so relatively high heat is generated even during low-speed cutting, so it cannot exhibit a better effect in terms of heat resistance. , When added in excess of 3.0% by weight, the content of the cubic carbide phase, which has a relatively weaker bonding strength with the bonding phase than the tungsten carbide (WC), increases, resulting in increased particle dropping (chipping) by welding, which in turn adversely affects tool life. Because it gives.

In addition, the cemented carbide according to the present invention is preferably manufactured by a vacuum sintering method to have the following micro-structure characteristics using the above composition.

The present invention has a constitutional feature in limiting the microstructure characteristics of the cemented carbide as described above, and the particle size of the 5a group cubic carbide and WC is defined as the maximum inscribed circle diameter inside the phase shape, as shown in FIG. 1. .

First, if the distribution of fine WC having a WC average particle size of less than 3 µm, which is the main material constituting the cemented carbide, is too large, the toughness of the sintered body is deteriorated, and if the distribution of granulated WC exceeding 5 µm is too large, the wear resistance of the sintered body is reduced and cutting Since particle detachment due to welding may occur largely, it is most preferable to maintain the average particle size in the range of 3.0 to 5.0 μm.

In addition, when the particle size of the group 5a cubic carbide exceeds 1.5 μm, as shown in the cutting test results of Examples and Comparative Examples of the present invention, chipping resistance and abrasion resistance are lowered, so 1.5 μm or less is preferable. It is more preferably maintained in the range of 0.01 to 1.5 µm.

Further, the cemented carbide according to the present invention is characterized in that it does not form a binder-enriched surface area.

In addition, in the cemented carbide according to the present invention, it is preferable that the area ratio of WC particles having a size of 1.0 to 6.0 μm in the cross-section of the cemented carbide is 80% or more of the total WC particle area of the cross-section.

In addition, one or more coating layers made of a carbide, carbonitride, carbonitride, or oxide of a metal formed by a CVD or PVD method may be formed on the cemented carbide base material according to the present invention.

The cemented carbide according to the present invention is expected to be particularly useful for machining difficult-to-cut materials such as stainless steel, which is superior in chipping resistance, compared to a conventional cemented carbide for cutting tools.

1 is a view for explaining the method used to measure the size of the carbides in the embodiment of the present invention and the particles constituting the microstructure of the cemented carbide.
2 is an optical microscope photograph of a cross section of a cemented carbide prepared according to an embodiment of the present invention.
3 is a photograph showing a cross-sectional structure of a cemented carbide manufactured according to an embodiment of the present invention.
4 is a photograph showing a cross-sectional structure of a cemented carbide prepared according to a comparative example.

Hereinafter, the present invention will be described in more detail based on examples of the present invention. However, the following examples are only examples to help the understanding of the present invention, and thus the scope of the present invention is not reduced or limited.

Production of cemented carbide

The present inventors prepared sintered bodies having different particle sizes and compositions as shown in Table 1 below.

The blending method for all compositions was compounded for 6 to 9 hours in accordance with the characteristics of an attrition mill with a forced grinding effect because the compound cantilever is in a jar. At the time of compounding, a starting composition raw material was used, a cemented carbide ball corresponding to 30% by volume of the total volume of the jar and ethanol corresponding to 30% by volume of the total volume of the container.

After the slurry formulated through this process was assembled through a spray dryer, it was pressed and sintered in the form of CNMG120408.

Raw material composition and sintering method of the sintered body according to Examples and Comparative Examples of the present invention division Composition (% by weight) Sintering WC Co NbC TaC TaNbC TiC ZrC Temperature
(℃) Sintering
Way Example 1 90.0 8.0 2.0 1450 vacuum Example 2 90.0 8.0 2.0 1450 vacuum Example 3 90.0 8.0 2.0 1450 vacuum Comparative Example 1 90.0 8.0 2.0 1450 vacuum Comparative Example 2 86.0 8.0 6.0 1450 vacuum Comparative Example 3 90.0 8.0 2.0 1450 vacuum Comparative Example 4 90.0 8.0 2.0 1450 vacuum Comparative Example 5 90.0 8.0 2.0 1450 vacuum Comparative Example 6 90.0 8.0 1.0 1.0 1450 vacuum Comparative Example 7 92.0 8.0 1450 vacuum

Hereinafter, differences between the manufacturing conditions of Examples 1 to 3 and Comparative Examples 1 to 7 of the present invention will be described in detail.

<Examples 1 to 3>

Examples 1 to 3 are for confirming the effect on the physical properties of the cutting tool when the particle size of the 5a group cubic carbide is the same and the composition is different. It is a cemented carbide obtained by sintering by the sintering method as shown in Table 1 to confirm the change in cutting performance according to the composition change of cubic carbide.

<Comparative Example 1>

Comparative Example 1 is for confirming the effect on the physical properties of the cutting tool when the particle size of Group 5a cubic carbide Nb is different from Example 1, and the composition of WC, Co and cubic carbide are the same and different milling conditions are used. It is a cemented carbide obtained by making the upper limit of the particle size of cubic carbide to a level of 0.01 to 4.0 µm higher than that of Example 1, followed by sintering in the same sintering method as in Example 1.

<Comparative Example 2>

Comparative Example 2 is for confirming the effect on the physical properties of the cutting tool when the content of the group 5a cubic carbide Ta is different from Example 2, compared to Example 2, WC weight of 86% by weight and group 5a cubic carbide The content of Ta is 6.0% by weight, and other conditions are cemented carbides obtained by sintering in the same sintering method as in Example 2.

<Comparative Examples 3 to 4>

Comparative Examples 3 to 4 are for confirming the effect on the physical properties of the cutting tool when the type of cubic carbide is different from Example 1, using the 4a group cubic carbide TiC and ZaC to sinter in the same sintering method as in Example 1 It is a cemented carbide obtained.

<Comparative Example 5>

Comparative Example 5 is for confirming the effect on the physical properties of the cutting tool when the average particle size of the WC is different from Example 1, the average particle size of the WC is 6.0㎛ larger than the present invention, the rest of the conditions are the same as Example 1 It is a cemented carbide obtained by sintering in the same way.

<Comparative Example 6>

Comparative Example 6 is to check the effect on the physical properties of the cutting tool when mixing the 5a and 4a group cubic carbide, unlike Example 1, WC average particle size of 4.2㎛ and 4a group cubic carbide TiC 1 weight % And 5a group of cubic carbide NbC 1% by weight, respectively, and the particle size is the same as in Example 1, the cemented carbide obtained by sintering.

<Comparative Example 7>

Comparative Example 7 is a cemented carbide obtained by sintering in the same sintering method as in Example 1, without adding cubic carbide except WC, and applying the average particle size of WC in the same manner as in Example 1.

Analysis of microstructure of cemented carbide

After cross-polishing the cross-sections of the cemented carbide according to Example 1 and Comparative Example 1 prepared as shown in Table 1, microstructures were observed using an optical microscope.

Figure 2 shows a cross-section of a cemented carbide prepared in accordance with Example 1 of the present invention, as shown in Figure 2, the cemented carbide prepared according to Example 1 is even in all areas without a binder enrichment layer in the surface area of the cubic carbide It can be seen that it is distributed.

In addition, FIGS. 3 and 4 are photographs obtained by observing the microstructures of Examples 1 and 1 with an optical microscope, respectively. It can be seen that it is relatively large.

The particle size and area ratio of WC, Co, and added cubic carbide on the microstructure were quantitatively measured using an image analyzer, and the results are shown in Table 2 below.

Average particle size and particle size distribution of carbides constituting the cemented carbide according to Examples and Comparative Examples of the present invention division WC Co Group 5a carbide Group 4a carbide weight% Average particle size
(um) weight% weight% Particle size distribution
(um) weight% Particle size distribution
(um) Example 1 90.0 4.0 8.0 2.0 0.01~1.5 Example 2 90.0 4.1 8.0 2.0 0.01~1.5 Example 3 90.0 4.0 8.0 2.0 0.01~1.5 Comparative Example 1 90.0 4.3 8.0 2.0 0.01~4.0 Comparative Example 2 86.0 4.0 8.0 6.0 0.01~1.5 Comparative Example 3 90.0 4.1 8.0 2.0 0.01~1.5 Comparative Example 4 90.0 4.0 8.0 2.0 0.01~1.5 Comparative Example 5 90.0 6.0 8.0 2.0 0.01~1.5 Comparative Example 6 90.0 4.2 8.0 1.0 0.01~1.5 1.0 0.01~1.5 Comparative Example 7 92.0 4.5 8.0

In addition, although not shown in Table 2 above, as a result of analyzing the particle size of WC for all cross-sections of the cemented carbides of Examples 1 to 3 using an image analyzer, particles having a size of 1.0 to 6.0 μm are 80% of the total WC area It was confirmed to exceed.

In Table 2, the particle size distributions of groups 4a and 5a are represented as 0.01 to 1.5 μm. The particle sizes of cubic carbides of groups 4a and 5a are substantially 1.5 μm or less, and the lower limit of 0.01 μm is practiced in the present invention. The minimum size that can be identified by the image analyzer used in the example. Therefore, it does not mean that particles smaller than 0.01 µm are not present.

CVD Preparation of coated cutting tools

Using a cemented carbide having the above composition and microstructure characteristics as a base material, a hard thin film layer was formed on the surface of the cemented carbide using a CVD method commonly used in the art to prepare a coated cutting tool.

The structure of the thin film is composed of a four layer structure of TiN-TiCN-Al ₂ O ₃ -TiN, the first TiN layer is formed to a thickness of 0.5㎛, and the TiCN layer is 4.5㎛ by medium temperature (700 ~ 950 ℃) CVD method It was formed to a thickness, the Al ₂ O ₃ layer was formed to a thickness of 1.5㎛, the outermost TiN layer was formed to a thickness of 0.5㎛.

Cutting performance evaluation

The cutting test is for evaluating the wear resistance and toughness (chipping resistance) of a cutting tool and was conducted in the following two methods.

(1) Cutting conditions for evaluation of wear resistance

Workpiece: STS316

Cutting speed: 200 m/min.

Feed (supply): 0.25 mm/rev

Cutting depth: 1.5 mm

Cutting tip shape: CNMG120408

Wet cutting evaluation: Side wear after 6 minutes cutting (Flank Wear, VB)

(2) Cutting conditions for toughness (chipping resistance) evaluation

Workpiece: STS316-2 hole

Cutting speed: 200 m/min.

Feed (supply): 0.25 mm/rev.

Cutting depth: 1.5 mm

Cutting tip shape: CNMG120408

Wet cutting evaluation: Time to end of life due to chipping and breakage (measured value is 5 times average value)

Table 3 shows the results after evaluation of the cutting performance as described above.

Evaluation results of wear resistance and toughness (chipping resistance) of cutting tools according to Examples and Comparative Examples of the present invention division Cutting performance Abrasion resistance tenacity Amount of wear (mm) End of life time (seconds) Example 1 0.180 225 Example 2 0.182 220 Example 3 0.181 225 Comparative Example 1 0.220 200 Comparative Example 2 0.230 160 Comparative Example 3 0.240 190 Comparative Example 4 0.243 195 Comparative Example 5 0.230 183 Comparative Example 6 0.235 191 Comparative Example 7 0.255 200

As can be seen from Table 3, in the case of a coated cutting tool made of a cemented carbide according to Examples 1 to 3 of the present invention, it was found that the abrasion resistance as well as the toughness (chipping resistance) were significantly improved compared to Comparative Examples 1 to 7 Can be.

Specifically, in Comparative Example 1, which has a larger particle size of Group 5a cubic carbide than Example 1, the wear resistance and toughness (chipping resistance) of each side are 0.220 mm and the end-of-life time is 200 seconds, which is better than in Example 1 This means that maintaining the particle size of group 5a cubic carbide at a level of 1.5 µm or less significantly affects wear resistance and toughness (chipping resistance).

In addition, in Comparative Example 2 in which the content of Group 5a cubic carbide was 6 wt% higher than in Example 2, the side wear amount was 0.230 mm and the end-of-life time was 160 seconds, which was significantly lower than in Example 2. Therefore, in order to improve the wear resistance and toughness, it is required to maintain the content of the cubic carbide of group 5a at 3% by weight or less.

In addition, compared to Example 1, the average particle size of WC is similar, and in the case of Comparative Examples 3 to 4 using a group 4a cubic carbide, the side wear amount is 0.240 to 0.243 mm and the end-of-life time is 190 to 195 seconds. Compared to the field, it falls significantly. In other words, it can be seen that the type of cubic carbide also affects the cutting performance (abrasion resistance and toughness).

In addition, in the case of Comparative Example 5, which has a larger WC average particle size than Example 1, the side wear amount is 0.230 mm and the end-of-life time is 183 seconds, and the average particle size of WC also significantly affects wear resistance and toughness (chipping resistance). Able to know.

In addition, unlike Example 1, in the case of Comparative Example 6 using a cubic carbide mixed with Groups 4a and 5a and having a similar WC average particle size, the end-of-life time is 191 seconds, which is somewhat lower than in Example 1, but the amount of side wear is It can be seen that 0.235mm was significantly reduced.

In addition, in the case of Comparative Example 7 containing no cubic carbide at all, the toughness (chipping resistance) was secured to some extent, but it was confirmed that the abrasion resistance was significantly reduced compared to Example 1 as well as other Comparative Examples 1 to 6.

From the evaluation results of cutting performance according to Examples 1 to 3 and Comparative Examples 1 to 7 as described above, to the existing cemented carbide through control of the average particle size, type, content and particle size of WC, cubic carbide Compared with the wear resistance, it has been confirmed that a cemented carbide with significantly improved toughness (chipping resistance) can be obtained, and such a cemented carbide can be suitably used for the processing of difficult-to-cut materials requiring good chipping resistance.

Claims (4)

WC: 84 ~ 94.8% by weight, Co: 5 ~ 12% by weight, Group 5a carbide: 0.1 ~ 3.0% by weight, and a cemented carbide containing inevitable impurities,
In the microstructure, the particle size of the 5a group cubic carbide is 1.5 µm or less, and the average particle size of WC is more than 3.5 µm to 5.0 µm,
Carbide alloy characterized in that the area ratio of WC particles of 1.0 ~ 6.0㎛ size in the cross-section of the cemented carbide is 80% or more of the total WC particle area of the cross-section. According to claim 1,
Carbide alloy, characterized in that the particle size of the group 5a cubic carbide is 0.01 ~ 1.5㎛. According to claim 1,
The cemented carbide is a cemented carbide, characterized in that there is no binder hatching surface area. delete

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