KR20130002488A - Sintered body for cutting tools and manufacturing method for the same - Google Patents

Abstract

PURPOSE: A sintered body for a cutting tool and a manufacturing method thereof are provided to reduce oxidation by using a raw material with particles having a size of 0.5-3.0 micrometers. CONSTITUTION: A sintered body for a cutting tool is formed by mixing hard powder composed of metal carbide, metal nitride, or carbonitride with metal powder. The average particle size of the hard powder is 0.5-3 micrometers, and the coalescence rate between particles of the hard powder is more than 70%.

Description

Sintered body for cutting tools and manufacturing method thereof {SINTERED BODY FOR CUTTING TOOLS AND MANUFACTURING METHOD FOR THE SAME}

The present invention relates to a sintered compact sintered by mixing hard ceramic powder and a binder metal powder and a method of manufacturing the same. More specifically, the hard ceramic powder has an average particle diameter of 500 nm or more, which is suitable for mass production. The present invention relates to a sintered compact and a method for manufacturing the same, which form a hard tissue having no core in the microstructure of the microstructure, increase the coalescence ratio of the hard phase particles, and control the metal-bonded phase content between the surface and the interior, thereby greatly improving cutting performance. .

Wear-resistant tools and cutting tools used in metal cutting are mainly WC-Co cemented carbide, TiC or Ti (C, N) -based cermet, and other ceramic or high speed steel.

The WC-Co cemented carbide is made of cobalt and tungsten having a strong strategic material property and has a high price disadvantage.

On the other hand, the cermet refers to a composite consisting of a ceramic hard phase and a metal bonded phase, in particular in the field of cutting tools, based on TiC or Ti (C, N), hard such as WC, NbC, TaC, Mo ₂ C Ceramics sintered under vacuum, hydrogen or argon atmosphere by mixing a hard phase powder containing some ceramics and a binder phase powder composed mainly of metals such as nickel (Ni), cobalt (Co) and / or iron (Fe). It means a metal composite sintered body.

Cermet has attracted attention as a substitute for WC-Co cemented carbides because of its high hardness, chemical stability at high temperatures, low specific gravity, and low raw material prices. In addition, the low toughness of WC-Co cemented carbide is a limiting factor in application expansion.

On the other hand, in the case of manufacturing the cermet using TiC, a sintered metal such as nickel (Ni), cobalt (Co) and / or iron (Fe) is used, in this case, compared to the WC-Co combination Since the wetting angle is large, rapid grain growth of TiC occurs, resulting in a drop in toughness.

The problem with the cermet using TiC is that TiN is added to TiC to form Ti (C, N), which is more thermodynamically stable and has a finer structure, thereby increasing the toughness to some extent.

In addition, in the microstructure of a conventional TiC-based or Ti (C, N) -based cermet sintered body, a solid solution between a core usually present as TiC or Ti (C, N) and other carbide added to surround the core ( A core / rim structure is formed with a rim composed of solid-solution: (Ti, M1, M2 ...) (C, N). As such, since the rim structure surrounding the core is a tissue having higher toughness than TiC or Ti (C, N) constituting the core, it may help to improve the toughness of the cermet.

However, since there is a core that causes brittle cermet brittleness, there is a problem that the toughness is lowered compared to the WC-Co cemented carbide, so that the WC-Co cemented carbide cannot be completely replaced.

As a method for solving this problem, Korean Patent Publication Nos. 2004-0009859, 2007-0099056, 2005-0038163, 2005-0032533, 2007-0017564, etc., include IVa, Va, And a hard phase powder composed of carbide, carbonitride, or a mixture of two or more metals selected from Group VIa metals, including titanium, consisting of a solid solution phase without a core structure and a sintered body without a core structure. And a method for producing the same are disclosed.

In addition, in the case of the sintered body disclosed in the published patents, the particle size of the solid solution powder having no core structure as a starting material is limited to 200 nm or less, and thus the method of miniaturizing the structure and lowering the sintering temperature is used.

However, when the mass production of at least 100Kg or more, as disclosed in the above-mentioned patents, when the nano-size powder of 200 nm or less is used as the starting material of the sintered body, since the powders are easily aggregated and oxidized, The manufacturing method has a problem that mass production is difficult.

Furthermore, in the case of the sintered body disclosed in the above-mentioned patent, the particle size of the solid solution powder is limited to 200 nm or less, but the metal binder phase contains about 20% by weight in order to obtain high fracture toughness. If kept high, it will be difficult to obtain the hardness and wear resistance required for the cutting tool. For example, the demand for high speed and high feed is increasing in recent cutting processes. In order to cope with the high speed and high feed cutting environment, at least 15 GPa of hardness must be secured, but it is difficult to satisfy the sintered bodies disclosed in the above-mentioned patents. .

Accordingly, in the case of TiWC or TiWCN-based solid-solution alloys proposed so far, the use of high-speed conditions is partially limited, and additional processes such as coating (physical vapor deposition or chemical vapor deposition) are applied to compensate for the disadvantages of the base metal. It is true.

The present invention has been researched and developed in order to solve the above-mentioned problems of the prior art, and does not use ultra-fine particles of less than 100 nm, while mass production is easy, while controlling the coalescence rate of the microstructured hard particles and the metal-bonded phase of the surface part and the inside. The object of the present invention is to provide a sintered compact for cutting tools that can be suitably used as a replacement for WC-Co-based cemented carbide by simultaneously improving toughness and wear resistance through a difference in content of (Co, Ni, or Fe).

Moreover, another subject of this invention is providing the manufacturing method which can obtain said sintered compact.

(1) As a means for solving the above problems, the present invention provides a sintered body obtained by mixing and sintering a hard phase powder composed of carbide, nitride or carbonitride of a metal and a binder phase metal powder which combines the hard phase powder. The average particle size of the hard phase powder is 0.5 to 3 μm, the coalescence rate between particles constituting the hard phase powder in the microstructure of the sintered body is 70% or more, and the content of the bonding phase of the surface portion of the sintered body is 30 It provides a sintered body characterized in that ~ 70% small.

In the sintered compact according to the above (1), the hard phase powder is composed of titanium and carbides, nitrides or carbonitrides of at least one metal selected from Groups IVa, Va, and Group VIa of the periodic table. The core structure may not be formed.

In addition, in the sintered compact according to (1), the metals constituting the hard phase powder are preferably formed in the ratio of the following [Formula 1].

[Formula 1]

Tix, Wy, Mz

(Where M is an element of groups IVa, Va, and VIa on the periodic table excluding Ti and W, where x + y + z ≦ 1, 0.1 ≦ y + z ≦ 0.5, 0 ≦ z <0.5)

In addition, in the sintered compact according to (1), the bonding phase metal is preferably selected from Co, Ni and Fe as one kind or a mixture of two or more kinds, and 4 to 18 wt% is preferably included.

(2) As a means for solving the other problem, the present invention, the average particle size is 0.5 ~ 3㎛ mixed hard phase powder made of metal carbide, nitride or carbonitride and the combined phase metal powder to combine the hard phase And a step of molding the mixed powder, and pressure sintering the molded powder, wherein the pressure sintering is performed at a rate of 5 ° C./min to 20 ° C./min between 400 ° C. and sintering temperature. after that, under the conditions of a sintering temperature of 1380 ~ 1450 ℃, the pressing force _{40 ~ 120MPa Ar, N 2,} CH 4, H 2 1 are carried out in individually or in combination of two or more mixed gas atmosphere, the surface of bonding-phase content of the sintered body after the hot pressing It provides a method for producing a sintered body, characterized in that 30 to 70% smaller than the inside.

In the production method according to the above (2), it is preferable that the coalescence rate between the microstructured hard powder particles of the sintered compact is 70% or more.

In the manufacturing method according to the above (2), it is preferable that the sintered compact does not have a core structure.

The sintered compact and its manufacturing method according to the present invention can be expected the following effects.

First, since the sintered compact according to the present invention uses a particle size of 0.5 μm to 3.0 μm of the starting raw material, it is less oxidized and less coagulates as compared to the conventional sintered compact using ultra-fine particles of 200 nm or less. It is easy to control the mixing, so it is suitable for mass production.

Second, when the particle size of the starting raw material is 500 nm or more and sintered by pressure sintering, compared to the sintered body using the raw material of 200 nm or less, the size of the microstructured hard phase particles after sintering relatively increases the size of the hard phase particles. This increases, so that the coalescence rate between the particles constituting the hard phase can be maintained at 70% or more. Accordingly, since the bonding force between particles increases, resistance to breakage of the edge part due to cracking or dropping of particles when used as a cutting tool increases, so that it is possible to replace the conventional cermet or WC-Co cemented carbide material.

Third, since the sintered compact according to the present invention can maintain the content of the metal bonded phase at 18% by weight or less, it is possible to eliminate a problem such as a decrease in wear resistance of the sintered compact due to the increase in the content of the metal bonded phase.

Fourth, since the sintered compact according to the present invention has a metal binder phase content of at least 50% or less at the surface portion of the sintered compact, the sintered compact having a higher hardness than the sintered compact can be realized, thereby increasing wear resistance when used as a cutting tool. In addition, since the inside of the sintered body maintains much more metal-bonded phase content than the surface, the sintered body can function as a shock mitigation against chipping and breakage due to high hardness of the surface part, thereby improving both wear resistance and toughness of the sintered body.

Fifth, the manufacturing method of the sintered compact according to the present invention can form a coalescing ratio between particles by 70% or more through pressure sintering, and at the same time achieve a relative density of 99.8% or more that can be used as a cutting tool.

BRIEF DESCRIPTION OF THE DRAWINGS In this invention, it is schematic which shows the measuring method of the coalescence rate between hard phase particle | grains.
2 is a microstructure photograph of a sintered body according to an embodiment of the present invention.
3 is a graph showing the results of measuring the hardness of the surface portion and the interior of the sintered body according to an embodiment of the present invention.

Hereinafter, the sintered compact according to a preferred embodiment of the present invention will be described in detail, but the present invention is not limited to the following examples. Therefore, it will be apparent to those skilled in the art that the present invention may be variously modified without departing from the technical spirit of the present invention.

Also, the singular forms used to describe the embodiments of the present invention are intended to include the plural forms as well, unless the phrases clearly indicate the opposite.

[Definition of Terms]

In the present invention, as shown in Fig. 1, the coalescing between the particles, as shown in Figure 1, the hard particles and the particles are bonded to each other by sintering to form a neck (neck), at least one of the cabinet of the formed neck is 90 ° It means the bonding state which consists of the following.

In addition, when the microstructure of the sintered body is observed with a scanning electron microscope (SEM) of 3000 magnification, the percentage of coalescence between particles means a percentage of the number of particles coalesced to the total number of hard phase particles observed.

In addition, the "surface part of a sintered compact" means the part to the depth of 30 micrometers from the surface of a sintered compact.

In addition, the "bonding phase content of the surface portion" means the average of the content of the binding phase measured at 0.01㎛ interval from the surface to 30㎛ depth.

In addition, "inner" means the area from the boundary of the surface portion of the sintered body to the center of the sintered body.

In addition, "internal binding phase content" means the average of the content measured at 0.01 μm interval from the boundary of the surface of the sintered body to the center of the sintered body.

The sintered compact according to the present invention is a sintered compact obtained by mixing and sintering a hard phase powder composed of carbide, nitride, or carbonitride of a metal and a binder metal powder which combines the hard phase powder, and the average particle size of the hard phase powder is 0.5. ~ 3㎛, the coalescence rate between the particles constituting the hard phase powder in the microstructure of the sintered body is 70% or more, the content of the bonding phase of the surface portion of the sintered body is 30 ~ 70% less than "inside" do.

The present inventors have researched and developed to obtain a sintered compact suitable for cutting tools because of excellent toughness and wear resistance without using ultra-fine particles of 200 nm or less, which are not easy to mass production in a hard phase. As it increases, the "breaking toughness value" representing the item of toughness in the cutting tool increases, which is advantageous for the cutting tool, especially when both sides of the neck formed between hard particles exceed 90 ° so that both particles act as one particle. When applied as a cutting tool, the wear resistance may be deteriorated due to the dropping of coarse particles when applied as a cutting tool.However, when the cabinet angle of the combined particles is kept at 90 ° or less, the impact force is applied by using the bonding force between the particles. While increasing the resistance to sintering, the adverse effects that may appear during grain coarsening can be minimized. It revealed that to increase toughness. In addition, by controlling the sintering process, reducing the content of the metal binder phase present on the surface of the sintered body and increasing the content of the internal binder phase increases the wear resistance required for the cutting tool and improves the toughness against impact. The present invention has been found to extend the range that can be substituted for cutting tools manufactured with -Co cemented carbide.

When the coalescence rate between the hard phase particles is less than 70%, the resistance against edge breakage is not sufficient, so that the coalescence rate between the hard phase particles is 70% or more.

In addition, when the difference in the content of the metal-bonded phase between the surface portion and the interior is less than 30%, the effect of improving the wear resistance is not sufficient, so the difference in the content of the metal-bonded phase between the surface portion and the interior is preferably more than 30%. . However, when the difference in the content of the metal bonding phase of the surface portion exceeds 70%, problems such as particle dropping occur, and less than 70% is preferable.

In the sintered compact according to the present invention, the hard phase is composed of titanium and carbides, nitrides or carbonitrides of at least one metal selected from Groups IVa, Va, and Group VIa of the periodic table, and the sintered compact has a core structure ( core-rim structure) is preferred because when the core structure is formed in the sintered body, the fracture toughness of the sintered body is lowered due to the presence of a core that is brittle and acts as a crack propagation path.

In addition, in the sintered compact according to the present invention, the metals constituting the hard phase powder are preferably formed in the ratio of the following [Formula 1].

[Formula 1]

Tix, Wy, Mz

(Where M is an element of groups IVa, Va, and VIa on the periodic table excluding Ti and W, where x + y + z ≦ 1, 0.1 ≦ y + z ≦ 0.5, 0 ≦ z <0.5)

As shown in [Formula 1], in the carbide, nitride or carbonitride mainly composed of titanium (Ti), the core elements excluding solid phases such as cobalt (Co), nickel (Ni) or iron (Fe) are two or more solid solutions When generating the state, the difference in the molar ratio of titanium (Ti) and tungsten (W) has a microstructural difference that determines the formation of a brittle core after sintering.

Specifically, in the case of using titanium (Ti) as a main element, when maintaining the molar ratio between the metal elements defined in the present invention, a bonded phase such as cobalt (Co), nickel (Ni), or iron (Fe) included in the sintered body is used. It is thermodynamically stable for the core elements to be present in the solid solution state between titanium and other added hard metal elements to be added, rather than as a single phase in TiC or TiCN states of titanium alone. Therefore, a solid structure is not formed by forming a solid solution.

On the other hand, when using titanium (Ti) as the main element, when the molar ratio between the metal elements defined in the present invention deviates from, for example, in the [Formula 1] z or 0 in the binary system or z is a non-zero ternary system In the case of y or y + z value of less than 0.1, the titanium (Ti) component increases in the hard phase, so that titanium (Ti) which exists alone after sintering is generated, and titanium (Ti) which is present alone is very brittle. Alternatively, the core is formed of TiCN to form a core structure. On the other hand, if the y or y + z value exceeds 0.5, brittle cores are not formed, but carbides of IVa, Va, and VIa elements including tungsten (W) form secondary phases and remain in solid solution tissue. This reduces the bonding strength between the solid solution particles and lowers the resistance to impact. Therefore, the metal constituting the hard phase powder is preferably made in the ratio of the above [Formula 1].

In addition, in the sintered compact according to the present invention, the binder phase metal powder is one or a mixture of two or more selected from cobalt (Co), nickel (Ni) and iron (Fe), it is contained in 4 to 18% by weight If the content is less than 4% by weight, the metal bonding phase is insufficient, and the bonding strength with the hard phase WC is reduced, making it difficult to normalize alloying. If the content is more than 18% by weight, the amount of the metal bonding phase is high due to the decrease in hardness due to the presence of the metal bonding phase. This is because it is difficult to cope with high feed cutting conditions.

In addition, the method for producing a sintered compact according to the present invention comprises mixing a hard phase powder composed of carbide, nitride or carbonitride of a metal and a binder phase metal powder combining the hard phase with an average particle size of 0.5 to 3 µm. Forming a powder, and pressure sintering the molded powder, wherein the pressure sintering is performed at a rate of 5 ° C./min to 20 ° C./min between 800 ° C. and sintering temperature, and a pressing force of 40 to 120 MPa. It is carried out under one or two or more of the mixed gas atmosphere of Ar, N ₂ , CH ₄ , H ₂ under the conditions of, characterized in that the bonding phase content of the surface portion of the sintered body after pressure sintering is 30 to 70% smaller than the inside . That is, the present invention is characterized by performing a pressurization which is not normally performed in the corresponding section while increasing the temperature increase rate.

In the production method according to the present invention, the reason for the numerical limitation of the average particle size of the raw material powder and the binding phase content of the surface portion of the sintered compact is the same as described above.

If the temperature increase rate between 800 ℃ and sintering temperature is less than 5 ℃ / min, the decarburization / denitrification reaction that causes mass movement of the surface and inside during sintering is insufficient, and if it exceeds 20 ℃ / min, normal alloying and densification of the sintered body Since it is hard to occur, it is preferable that the temperature increase rate in the said temperature range is 5 degreeC / min-20 degreeC / min.

In addition, since the normal densification alloy is difficult to implement when sintering only under the conditions of a temperature increase rate of 5 ° C./min to 20 ° C./min, in the embodiment of the present invention, simultaneously applying pressurization during temperature increase, decarburization / dedusting by rapid temperature increase. By suppressing reaction, the normal sintered compact whose relative density is 99.8% or more is manufactured. Moreover, a more effective sintered compact can be manufactured by the combination of the gas used at the time of pressurization.

On the other hand, when the sintering temperature is less than 1380 ℃ because the normal densification between the hard phase and the metal bonding phase does not occur, pores and unhealthy structure may occur to cause a decrease in physical properties. In addition, when the sintering temperature is higher than 1450 ° C, excessive abnormal grain growth is caused, so that the sintering temperature is preferably maintained in the above range.

In addition, when the pressing force is less than 40MPa, the coalescence rate between the hard phase particles may not be satisfied more than 70%, and the relative density is also reduced, making it difficult to implement normal complexation. On the contrary, when the pressing force exceeds 120 MPa, the decomposition of carbon and nitrogen remaining in the alloy is insufficient, and thus there is a high possibility of generating defects such as pores and free carbon, which are unhealthy. In addition, in order to apply a pressing pressure of 120MPa or more in the sintering process, an additional sintering process cost is generated, which has the disadvantage of increasing production cost.

[Example]

Manufacture of Sintered Body

In order to prepare a sintered compact according to an embodiment of the present invention, first, a mixed powder of cobalt (Co) and nickel (Ni) as a metal bonding phase and 1,368 g of (TixWy) C powder having an average particle size of 0.5 to 3.0 µm as a starting material 252 g was prepared.

In addition, in order to compare and evaluate the characteristics of the sintered body manufactured according to the embodiment of the present invention, a composition using commercial TiC, TiN or TiCN-WC-Co / Ni and (Ti, W) C-Co / Ni Sintered bodies of Comparative Examples 1 to 6 were prepared. Specifically, in Comparative Example 1, 684 g of TiC and TiN powder having an average particle size of 1.2 to 2.0 μm, respectively, and in the case of Comparative Examples 2, 3 4 and 6, the particle sizes were respectively 500 nm and higher. 1,368 g of (TixWy) C powder, each of which was adjusted to different values as shown in Table 1, and 1,368 g of (TixWy) C powder having an average particle size of 350 nm in the case of Comparative Example 5, was used as a hard phase powder. At this time, the composition and content of the metal-bonded phase powder were the same as in the embodiment of the present invention.

In addition, ßt (content of carbides containing at least one of the groups IVa, Va, and VIa on the periodic table, which is generally added in small amounts as elements other than titanium (Ti) and tungsten (W)) is also an embodiment or comparative example of the present invention. In order to compare the physical properties of 1 to 6, all were prepared in the same 180g.

The powder thus prepared was milled for about 20 hours using an alcohol as a solvent and an Attritor through a carbide corner having a diameter of 5 mm. Through this milling process, a slurry in which the hard phase powder and the metal binder phase powder were mixed was obtained.

The mixed slurry was dried using a spray dryer, and then molded into a SNMG120408 and SPCN1203EDTR models at a pressure of 1000 kg / cm 2.

The molded product thus prepared was sintered by pressure sintering using a pressure sintering apparatus commonly used in this field under a mixed gas atmosphere of 99.5% Ar and 99.8% H ₂ .

At this time, in heating from the room temperature to the sintering temperature, the temperature increase rate was maintained at a rate of 10 ℃ / min, especially between 800 ℃ ~ 1380 ℃ intervals.

The pressure sintering was performed under conditions of a sintering temperature of 1380 ° C., a sintering time of 1 hour, and a pressing force of 60 MPa. Meanwhile, in the embodiment of the present invention, a mixed gas of argon (Ar) and hydrogen (H ₂ ) is used as the atmosphere gas, but if necessary, sintering in a vacuum state, or argon (Ar), nitrogen (N ₂ ), hydrogen ( One or two or more mixed gases selected from gases such as H ₂ ) and methane (CH ₄ ) may be used.

Through this process, a sintered compact having a composition shown in Table 1 below and showing a microstructure as shown in FIG. 2 was prepared. On the other hand, in the embodiment of the present invention, a solid solution carbide mainly composed of titanium (Ti) and tungsten (W) was used, but in addition to this carbide, hard carbide is usually added to a sintered body for cutting tools such as WC, NbC, TaC, and Mo ₂ C. Awards may also be included.

The component ratio of the metal component which comprises the hard phase of each sintered compact was measured using the plasma discharge component analyzer (GDOES).

In addition, in the microstructure of the manufactured sintered body, the determination of coalescence between particles is performed by scanning electron microscope (SEM) images of 3000 times magnification. As shown in FIG. It judged whether it was below or not, and measured the number of particle | grains whose cabinet angle is 90 degrees or less, and calculated it as the percentage as follows.

% Coalescing = (number of hard phase particles coalesced / total number of hard phase particles observed) x 100

Composition, microstructure, and hard phase core structure of the sintered compact according to the Examples and Comparative Examples of the present invention Kinds Core composition Raw material features Sintering Method Temperature rise rate
(℃ / min) Coalescing rate
(%) surface/
Center difference (%) x y Solid solution
Whether Granularity Comparative Example
One (TiC + TiN) _x + W _y C Non-employment 500nm or more Pressure 4 Less than 50 95 1.0 1.0 Comparative Example
2 TiCN _x + W _y C Non-employment 500nm or more Pressure 3 Less than 50 90 1.0 1.0 Comparative Example
3 (Ti _x , W _y ) C Solid solution 500nm or more Pressure 3.5 Less than 50 90 0.25 0.75 Comparative Example
4 (Ti _x , Wy) C Solid solution 500nm or more Pressure 4 Less than 50 95 0.92 0.08 Comparative Example
5 (Ti _x , W _y ) C Solid solution Less than 500nm Pressure 2 Less than 50 97 0.75 0.25 Comparative Example
6 (Ti _x , W _y ) C Solid solution 500nm or more vacuum 4.5 Less than 60 98 0.75 0.25 Comparative Example
7 (Ti _x , W _y ) C Solid solution 500nm or more Pressure 4.8 70 or more 100 0.75 0.25 Comparative Example
8 (Ti _x , W _y ) C Solid solution 500nm or more Pressure 20 70 or more 25 0.75 0.25 Example
One (Ti _x , W _y ) C Solid solution 500nm or more Pressure 10 70 or more 42 0.75 0.25 Example
2 (Ti _x , W _y ) C Solid solution 500nm or more Pressure 5 70 or more Over 50 0.75 0.25

As shown in Table 1, in Examples 1 and 2 of the present invention, by adjusting the composition of the starting raw material, the average particle size of 0.5 ~ 3㎛ and applying the pressure sintering conditions, without having a microstructured core structure A sintered compact having a coalescence rate of more than 70% between hard phase particles and a difference in composition between the surface and the inner metal bonding phase was 42% and 50%, respectively. In particular, in the case of Example 2, as shown in Figure 3, it was confirmed that the difference in the Co content between the surface portion and the center has a sloped structure with a difference of 50% or more.

On the contrary, Comparative Examples 5 and 6 having the same composition as the embodiment of the present invention are conditions that sinter the vacuum sintering or pressure sintering conditions that do not pressurize the conditions outside the range of the embodiment of the present invention (the same as the present invention in the case of vacuum sintering). The sintering temperature and time were applied, and in the case of pressure sintering conditions, the sintering conditions were the same as in the present invention, but the particle size of the solid solution powder was not satisfied. It was measured to be less than 50% and less than 60%.

In addition, Comparative Example 7 exhibited similar raw material usage and microstructure characteristics as the present invention, but did not show a difference in composition between the metal and the metal phase due to the temperature increase rate during sintering not reaching the range set in the present invention.

On the other hand, when carried out under the same conditions as in Comparative Example 8, the surface-internal metal bonding phase composition difference ratio (Sb / Ib) reached the range set in the present invention, but the densification of the sintered compact was performed because the temperature increase rate was too fast. Because of this, unhealthy structures such as pores and free carbon were generated inside the sintered body, indicating that the tool could not be used as a cutting tool.

In addition, in Comparative Examples 1 to 4, not only showed a microstructured core structure, but also all of the hard phases were measured to be less than 50%.

In addition, Comparative Example 7 shows the use of raw materials and microstructure similar to the present invention, but the temperature increase rate during sintering was different from the embodiment of the present invention, and there was no difference in the metal bonding phase between the surface and the inside.

On the contrary, in Comparative Example 8, the metal bonding phase composition difference ratio (Sb / Ib) between the surface portion and the inside reached the range set in the present invention, but the densification of the sintered compact did not occur because the temperature increase rate was too fast, so the inside of the sintered compact Unhealthy structures such as pores and free carbon have occurred, indicating that they cannot be used as cutting tools.

Characterization of Sintered Body

The inventors of the present invention have the effect of the difference between the microstructures (the presence or absence of the core structure and the difference in coalescing ratio) of the microstructures of Examples 1 and 2 and Comparative Examples 1 to 8 of the present invention on the physical properties (hardness and fracture toughness) of the sintered body. In addition, the impact of the application on the actual cutting tool was evaluated.

(1) Milling Wear Resistance Evaluation-GC250

The first milling abrasion resistance test uses GC250 cast iron as workpiece, cutting speed (vc) is 500 m / min, feed (feed) is 0.3mm / tooth, cutting depth (ap) is 2.0mm, cutting insert geometry is SPKN1203EDER, The coolant was performed under wet conditions, and the evaluation was performed by measuring the time until the side wear amount reached 0.2 mm under the above conditions.

(2) Milling Wear Resistance Evaluation-FCD600

The second milling abrasion resistance test used FCD600 ductile cast iron as the workpiece. FCD600 is a soft weldable workpiece compared to GC250. The cutting speed (vc) was 150 m / min, feed (supply) was 0.2 mm / tooth, cutting depth (ap) was 2.0 mm, cutting insert shape was SPKN1203EDER, cutting oil was performed under wet conditions, and the evaluation was performed under the above conditions. The wear test was performed by measuring the time until the side wear amount reached 0.2mm.

(3) Milling Toughness (Flaw Resistance) Evaluation

Milling fracture resistance evaluation was a method of measuring the time until the final failure after evaluating the wear resistance under the condition of (1), and the longer the time until the final failure, the chipping resistance due to continuous interruption during cutting or It was regarded as a sintered compact having good fracture resistance.

The evaluation results of the cutting performance evaluated by the above method, the hardness (applied Hv 2.0Kg load) and fracture toughness (50Kg load) of the sintered body are shown in Table 2 below.

Kinds Hardness (Hv) Fracture toughness
(MPam ^1/2) Cutting performance surface inside FCD600 GC250 Wear
(mm) Wear
(mm) Milling toughness Comparative Example 1 1300-1400 1300-1400 5.3 ~ 5.8 0.030 0.045 30 minutes Comparative Example 2 1300-1400 1300-1400 5.5-6.0 0.020 0.028 27 minutes Comparative Example 3 1200-1300 1200-1300 6.5 ~ 7.0 0.024 0.040 32 minutes Comparative Example 4 1300-1400 1300-1400 6.0-6.5 0.020 0.25 25 minutes Comparative Example 5 1400-1500 1400-1500 6.5 ~ 7.0 0.015 0.018 40 minutes Comparative Example 6 1350-1450 1350-1450 6.4 to 6.9 0.014 0.180 38 minutes Comparative Example 7 1400-1500 1400-1500 7.5 ~ 8.0 0.011 0.130 40 minutes Comparative Example 8 Not measurable Not measurable 4.0 ~ 5.0 Chipping, breaking Chipping, damage. Within 10 minutes Example 1 1700-1800 1400-1500 7.5 ~ 8.0 0.090 0.010 60 minutes Example 2 1700-1800 1400-1500 7.7 ~ 8.3 0.0010 0.012 70 minutes

※ In Comparative Example 8, the tool life could not be calculated due to premature chipping and breakage during cutting test due to the appearance of unhealthy tissue in the tissue (average of more than 8 corners of insert corner).

As confirmed in Table 2, the hardness of the sintered compact according to the embodiment of the present invention is equivalent to or greater than that of Comparative Examples 1 to 6. In addition, it can be seen that the fracture toughness, which greatly affects the durability of the cutting tool, was significantly improved compared to Comparative Examples 1 to 6.

Specifically, in the case of Comparative Examples 1 and 2 due to the influence of the use of non-solid raw materials, Comparative Examples 3 and 4 show a microstructured core structure under the influence that the composition does not satisfy the range defined in the present invention, In the embodiment of the present invention, it can be seen that the fracture toughness is lower than that of Comparative Examples 5 and 6 in which no core structure is shown.

On the other hand, Comparative Examples 5 and 6 have a low fracture toughness compared to the embodiment of the present invention, despite the absence of the core structure in the same manner as the embodiment of the present invention, which is hard in the microstructure of the sintered body according to the embodiment of the present invention. Comparative Examples 5 and 6 are judged to be a difference due to the coalescence rate of less than 60%, while the coalescence rate of the phase particles is greater than 70%, and Comparative Example 7 is a coalescence rate of the hard phase particles. Although satisfactory, the sintering conditions have different characteristics, and thus the wear resistance can be confirmed to be improved compared to the existing tool, but it can be seen that the toughness is inferior to the present invention.

In addition, even in the actual cutting performance test, the sintered bodies according to Examples 1 and 2 of the present invention had a delayed time of about 20% or more of the break point of the edge portion compared to Comparative Examples 1 to 8, and improved wear resistance.

From this, it can be seen that the sintered compact according to the embodiment of the present invention can be suitably used as a base material of a cutting tool for casting iron.

In addition, when the coating layer using the chemical vapor deposition method and the physical vapor deposition method is formed on the sintered body according to the embodiment of the present invention, since excellent wear resistance can be obtained, the sintered body according to the present invention compensates for the poor brittleness of the conventional cermet and further It may be possible to partially replace WC-based cemented carbide.

Claims (9)

A sintered compact obtained by mixing and sintering a hard phase powder composed of carbide, nitride, or carbonitride of a metal and a binder phase metal powder for bonding the hard phase powder,
The average particle size of the hard phase powder is 0.5 ~ 3㎛, the coalescence rate between the particles constituting the hard phase powder in the microstructure of the sintered body is 70% or more,
Sintered body characterized in that the content of the bonding phase of the surface portion of the sintered body is 30 to 70% smaller than the inside. The method of claim 1,
The hard phase powder is composed of titanium, carbides, nitrides or carbonitrides of at least one metal selected from Groups IVa, Va, and Group VIa in the periodic table, and the sintered compact is characterized in that no core structure is formed. . The method of claim 1,
The metal constituting the hard phase powder is a sintered body, characterized in that consisting of the ratio of the following [Formula 1].
[Formula 1]
Tix, Wy, Mz
(Where M is an element of groups IVa, Va, and VIa on the periodic table excluding Ti and W, where x + y + z ≦ 1, 0.1 ≦ y + z ≦ 0.5, 0 ≦ z <0.5) The method of claim 1,
The binder phase metal is a sintered compact, characterized in that it comprises 4 to 18% by weight as one or a mixture of two or more selected from Co, Ni and Fe. The method of claim 1,
On the sintered body is a sintered body characterized in that a thin film deposited by chemical vapor deposition or physical vapor deposition is formed. Mixing a hard phase powder composed of carbides, nitrides or carbonitrides of a metal having an average particle size of 0.5 to 3 μm and a binder phase metal powder for bonding the hard phase,
Shaping the mixed powder, and
Pressure sintering the shaped powder,
The pressure sintering was performed at a rate of 5 ° C./min to 20 ° C./min between 400 ° C. and sintering temperature, and then Ar, N ₂ , CH ₄ , One or two or more mixed gas atmospheres of H ₂ ,
A method for producing a sintered compact, characterized in that the content of the bonding phase in the surface portion of the sintered compact after pressure sintering is 30 to 70% smaller than that in the interior. The method according to claim 6,
Method for producing a sintered compact, characterized in that the coalescence rate between the fine structure of the hard phase powder particles of the sintered compact is 70% or more. The method according to claim 6,
The sintered body is a manufacturing method of the sintered body, characterized in that no core structure is formed. The method according to claim 6,
The method of manufacturing a sintered compact, characterized in that the thin film deposited by chemical vapor deposition or physical vapor deposition is formed on the sintered compact.

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