WO2014013715A1 - Superhard alloy imparted with low friction ability, method for producing same, and superhard tool - Google Patents

Abstract

The present invention is a superhard alloy in which particles of tungsten carbide (WC) are bound to each other through a binder metal, and in which crystal grains of hexagonal boron nitride (h-BN) are formed in a dispersed state in the binder metal that binds the particles of WC to impart a low friction ability to the superhard alloy. The superhard alloy is produced from a material that is prepared by mixing at least one B source component selected from the group consisting of B₂O₃, H₃BO₃, h-BN, WB and TiB₂ with a powder mixture prepared by mixing a WC powder with a metal powder capable of binding particles of WC to each other so that the B source component can be dispersed in the powder mixture. A superhard alloy powder in which the B source component is mixed in a dispersed state is compression-molded to produce a compression-molded article. The compression-molded article is nitrided in a pressurized nitrogen atmosphere, thereby producing a superhard alloy in which crystal grains of hexagonal boron nitride (h-BN) are formed in a dispersed state in the binder metal that binds particles of WC to each other.

Description

Cemented carbide provided with low friction reducing ability, manufacturing method thereof, and cemented carbide tool

[Technical Field] The present invention relates to a cemented carbide provided with a low friction reducing ability, a manufacturing method thereof, and a cemented carbide tool including a cutting tool and a mold.

While maintaining high impact resistance (bending strength) against impact load during cutting, lubricity is provided, excellent finished surface accuracy is maintained over a long period of use, and stable cutting performance is achieved. Carbide tools that demonstrate the above are being researched and proposed. As this type of cemented carbide tool, a titanium nitride (hereinafter referred to as TiN) is formed on the surface of a tool base made of tungsten carbide based cemented carbide, titanium carbonitride based cermet, or cubic boron nitride based ultra high pressure sintered material. And a hard coating layer such as a titanium carbonitride (hereinafter referred to as TiCN) layer and a composite nitride (hereinafter referred to as TiAlN) layer of titanium and aluminum have been proposed. Yes.

This type of carbide tool is used for cutting various steels and cast irons, for example. Furthermore, in order to increase the lubricity between the coated tool and the work material and reduce the cutting resistance, a coated tool in which a lubricating layer or a lubricating film is further formed on the surface of the hard coating layer is also known.

For example, a carbide tool for cutting is known in which a lubricating film is formed on the uppermost layer of a tool base to improve lubricity (see Patent Document 1). This type of cemented carbide tool is intended to improve lubricity by forming a coating of MoS ₂ or a mixture of MoS _{2 on} the surface of the hard coating layer formed on the surface of the tool base by using a sputtering method. .

As another example of this type of cemented carbide tool, a TiN layer, a TiCN layer, and a TiAlN layer formed on the surface of the tool base are further MOI (where M is Si, Zr) by an ion plating method. , Ni, Fe, Co, and Cr, and 0.2 ≦ Y <2) is formed to improve the lubricity by forming a lubricating film (for example, Patent Document 2).

As still another example, a carbide for cutting in which a lubricating film made of an amorphous silicon nitride film is formed on a hard coating layer made of a TiN layer, a TiCN layer, and a TiAl layer formed on the surface of a tool base. There is a tool (see Patent Document 3). This kind of carbide tool can suppress abnormal damage such as chipping and chipping when applied to wet interrupted cutting where impact and intermittent load act on the cutting edge, and over a long period of use, It is known to maintain excellent finished surface accuracy and exhibit stable cutting characteristics. This is because the amorphous silicon nitride film has excellent lubricity.

Furthermore, in the cemented carbide tool in which the tool base is formed of a tungsten carbide (WC) based cemented carbide sintered material, cubic boron nitride (hereinafter referred to as c-BN), hexagonal boron nitride is formed on the surface of the tool base. (Hereinafter referred to as h-BN) and amorphous boron nitride (hereinafter referred to as a-BN) formed a composite hard phase film that exhibits excellent chipping resistance and wear resistance Has been proposed (see Patent Document 4).

Japanese National Patent Publication No. 11-509580 JP 2000-233324 A JP 2011-51033 A JP 2011-194512 A

In the field of cutting materials such as various types of steel and cast iron, the automation of the cutting process has been greatly enhanced, and energy saving has been promoted along with labor savings for cutting work. Cost reduction is required. In addition to the cutting conditions for realizing such technical problems and reducing the cost, cutting under higher speed conditions is required.

Also, a mold used for molding a processing material such as a metal material into a certain shape is required to have a lubricity on the molding surface. However, it is extremely difficult to form a film with excellent lubricity on the surface of the tool base, like a tool for cutting, because of the structure of the mold that molds the work material on the inner peripheral surface. is there.

Therefore, the present invention aims to further speed up the cutting of the material to be cut and to improve the lubricity of the mold using the cemented carbide, so that the cemented carbide is excellent in low friction characteristics and its manufacture. The present invention has been proposed for the purpose of providing a method, a cutting tool using the cemented carbide as a substrate, and a cemented carbide tool including a die.

The inventors of the present invention have focused on h-BN, which is known as a solid lubricant, for improving the low friction characteristics of a cutting tool and further a carbide tool including a die.

As an example in which this h-BN is used for forming a lubricating layer on the surface of the substrate, there is an example in which it is used as a composite material when forming a coating layer of c-BN, but a tool substrate such as TiN is used. There is no example in which a lubricating layer is formed by forming a film alone on the surface. That is, h-BN alone is formed on the surface of the tool base and only reduces the mechanical performance of the tool when the coating layer of the carbide tool is formed. This is because it could not function as a lubricant for the tool.

Accordingly, the present invention provides a cemented carbide having excellent lubricity and high mechanical strength, and a method for producing the same, without adopting a configuration in which a lubricating layer is formed on the surface of the tool base as described above. Furthermore, the present invention is proposed for the purpose of providing a cutting tool using the cemented carbide as a tool base, and further a cemented carbide tool including a die.

The inventors of the present invention have improved lubricity and improved mechanical strength, thereby suppressing the occurrence of abnormal damage that occurs when used for grinding workpieces, etc., for long-term use. Over time, as a result of earnest research to develop cutting tools that maintain stable finished surface accuracy and exhibit stable machining characteristics, as well as carbide tools including molds, excellent low friction reduction ability Has succeeded in developing the present invention.

The present invention relates to a cemented carbide that achieves the above-described characteristics and a cemented carbide tool that uses the cemented carbide, and improves the lubricity of the cemented carbide constituting the tool base. Suppressing the occurrence of abnormal damage that occurs during machining such as cutting, maintaining excellent finished surface accuracy over a long period of use, and realizing stable machining characteristics.

First, the present invention is a tungsten carbide-based cemented carbide in which tungsten carbide particles are sintered and bonded with a bonding metal, and hexagonal boron nitride (h— This is a cemented carbide in which BN) is dispersedly formed. This cemented carbide is imparted with low friction reducing ability by dispersing and forming hexagonal boron nitride (h-BN) in a bonding metal that bonds the particles of tungsten carbide.

In the cemented carbide according to the present invention, at least a part of the tungsten carbide particles bonded by the bonding metal has a double structure of a tungsten carbide nucleus and a structure around the tungsten carbonitride.

In the cemented carbide according to the present invention, h-BN formed in the bonding metal that bonds the WC particles is preferably in the range of 10 to 1500 ppm in terms of boron (B). Further, the h-BN formed in the bonding metal that bonds the WC particles is preferably in the range of 10 to 1000 ppm in terms of boron (B), and more preferably in the range of 10 to 10 in terms of boron (B). It is desirable to be in the range of 500 ppm.

By the way, it is desirable that the crystal grains of h-BN deposited in the bonding metal that bonds the WC particles be 1 μm or less.

Furthermore, the present invention is a cutting tool using any of the above-mentioned cemented carbides as a tool base, and further a cemented carbide tool including a die.

The present invention is also a method for producing a cemented carbide with low friction reducing ability, wherein boron (B) is mixed in a mixed powder in which a tungsten carbide powder and a bonding metal powder for bonding between tungsten carbide particles are mixed. A cemented carbide powder in which a supply source is dispersed and mixed is manufactured, and then the cemented carbide powder is compression-molded to form a green compact, and then the green compact is nitrided in a nitrogen-pressurized atmosphere, Crystal grains of hexagonal boron nitride (h-BN) are dispersedly formed in a bonding metal that bonds the particles of tungsten carbide.

Here, the green compact is heated and sintered in a vacuum, and then nitriding treatment, whereby h-BN crystal grains are dispersedly formed in the bonding metal. It is desirable that the h-BN crystal grains are dispersed and formed in the crystalline metal as particles of 1 μm or less. The step of nitriding the green compact may be performed during the step of heating and sintering the green compact.

The B source used to form hexagonal boron nitride (h-BN) grains in the bond metal is from the group consisting of B ₂ O ₃ , H ₃ BO ₃ , h-BN, WB and TiB _2. One selected can be used.

In addition, another method for producing a cemented carbide with low friction reducing ability according to the present invention is to produce a cemented carbide powder in which a tungsten carbide powder and a bonded metal powder that bonds between tungsten carbide particles are mixed, Subsequently, the cemented carbide powder is compression-molded to form a green compact, and then a B supply source solution in which a B supply source is dissolved in a solvent is supplied from the surface of the green compact. The B supply source is dispersedly supplied, and then the green compact is nitrided in a nitrogen-pressurized atmosphere, and hexagonal boron nitride (h-BN) is bonded into the bonding metal that bonds the particles of the tungsten carbide. The crystal grains are dispersedly formed.

Here, the green compact is heat-sintered in a vacuum, and then subjected to nitriding treatment, whereby hexagonal boron nitride (h-BN) crystal grains are dispersedly formed in the bonding metal. The step of nitriding the green compact may be performed during the step of heating and sintering the green compact.

The B source solution used for forming hexagonal boron nitride (h-BN) grains in the binding metal is a solution containing 0.02 wt% or more and 4 wt% or less of the B supply source in terms of boron. It is desirable to use a solution dissolved in

The present invention provides a cemented carbide tool in which h-BN crystal grains are dispersedly formed in a bonding metal that bonds between WC particles constituting a WC-based cemented carbide, so that the bending strength is not reduced. Thus, the frictional resistance can be reduced while maintaining the bending strength required when processing is performed. Cutting tools using this cemented carbide as a tool base, and cemented carbide tools including dies, suppress the occurrence of abnormal damage when used in machining processes such as cutting and forming various metals. In addition, stable machining characteristics can be realized while maintaining excellent finished surface accuracy over a long period of use.

Further, the cemented carbide manufactured by adopting the manufacturing method according to the present invention is formed by nitriding a green compact in which a B supply source is dispersed in a nitrogen pressurized atmosphere. Part or all of the particles have a double structure of the WC nucleus and the surrounding structure of tungsten carbonitride, which further improves the low friction ability.

A cutting tool using the cemented carbide according to the present invention as a base, and further, a cemented carbide tool including a die is excellent in low friction characteristics and maintains a certain bending strength. Improves machining efficiency and extends the service life.

FIG. 3 is an X-ray absorption spectroscopy (XANES) spectrum analysis diagram showing that hexagonal boron nitride (h-BN) is formed in the bonded metal of the cemented carbide according to the present invention. It is the photograph which observed the structure | tissue of the cemented carbide which comprises the cemented carbide tool which gave the post-etching which mirror-finished the end surface of the cemented carbide tool formed using the cemented carbide based on this invention with the scanning electron microscope. It is a graph which shows the result of having measured the friction coefficient of the cemented carbide tool using the cemented carbide metal concerning this invention, and the conventional cemented carbide tool using the ball-on-plate method. The results of measuring the friction coefficient of a cemented carbide tool according to the present invention using a cemented carbide tool having a double structure of WC particles and a conventional cemented carbide tool using a ball-on-plate method. It is a graph to show.

The cemented carbide according to the present invention is a cemented carbide mainly composed of tungsten carbide (WC), in which hexagonal boron nitride (h-BN) crystal grains are dispersed in a bonding metal that bonds WC particles. It is formed and given a low friction reducing ability.

As the bonding metal of the cemented carbide according to the present invention, Co, Ni, Co—Ni alloy, Fe—Ni alloy, Co—W alloy in which 20 wt% or less of W, Cr, Mo, V is dissolved, Ni— A Cr alloy, Co—Cr—V alloy, Co—Ni—Cr alloy, Co—Ni—W—Cr alloy, Fe—Ni—Co—W—Cr—Mo alloy, or the like can be used. If the content of the bonding metal in the cemented carbide is less than 3% by weight relative to the entire cemented carbide, voids remain inside the alloy and the strength and toughness are reduced. Since the wear resistance is lowered, it is appropriate to be in the range of 3 to 30% by weight.

The cemented carbide according to the present embodiment is manufactured by the following process. First, a group consisting of B ₂ O ₃ , H ₃ BO ₃ , h-BN, WB, and TiB ₂ in a mixed powder obtained by mixing WC powder constituting the cemented carbide powder and metal powder that binds between WC particles. One B source selected from the above is dispersed and mixed. Next, paraffin wax is added to the cemented carbide powder material mixed with the B supply source to obtain a finished powder. Then, the cemented carbide finished powder mixed with the B supply source is compression-molded to obtain a green compact. Next, the green compact is degreased. Thereafter, the green compact is heat-sintered in vacuum, and then nitriding is performed in a nitrogen-pressurized atmosphere.

When a green compact made of cemented carbide powder mixed with a B supply source is nitrided, hexagonal boron nitride (h-BN) crystal grains are dispersed in the bonding metal that bonds the WC particles. Form.

Here, the B supply source is preferably determined in relation to the h-BN concentration interposed in the bonded metal, and is preferably in the range of 10 to 1500 ppm in terms of B, and desirably in terms of B. It is preferably in the range of 10 to 1000 ppm, more preferably in the range of 10 to 500 ppm. Further, the step of nitriding the green compact may be performed during the step of heating and sintering the green compact. Good.

Furthermore, the cemented carbide according to the present invention may be manufactured through the following steps. First, WC powder and binding metal powder are mixed, and further, paraffin wax is added to the mixed powder to obtain a finished powder. The cemented carbide finished powder is compression molded to form a green compact, and then the green compact is degreased. A B supply source solution in which a B supply source is dissolved in a solvent is applied to the surface of the defatted green compact, or impregnated from the surface of the green compact and penetrates into the green compact. The B supply source solution that has penetrated into the green compact diffuses into the green compact and finely disperses on the surface of the particles constituting the cemented carbide powder forming the green compact.

When water or alcohol is used as the solvent of the B supply source solution, B ₂ O ₃ or H ₃ BO _{3 that} is soluble in water or alcohol is used as the B supply source.

The green compact supplied with the B supply source solution from the surface is heated and sintered in a vacuum, and then is nitrided in a nitrogen-pressurized atmosphere, as in the manufacturing method of the above-described embodiment. This nitriding treatment may be performed during the step of heating and sintering the green compact.

The green compact made of the cemented carbide powder impregnated with the B source solution is subjected to nitriding treatment in the same way as in the above-described embodiment, so that hexagonal nitriding is formed in the bonding metal that bonds the WC particles. Boron (h-BN) crystal grains are dispersedly formed.

Incidentally, the B supply source solution supplied from the surface of the green compact is obtained by dissolving the B supply source in a solvent such as water or alcohol. Therefore, the B source used for the B source solution is one that can be dissolved in a solvent, water, or alcohol.

The concentration of the B supply source solution used here is preferably determined in relation to the concentration of h-BN interposed in the cemented metal of the cemented carbide formed by sintering the green compact. A dilute solution of 0.02 wt% (200 ppm) or more and less than 4 wt% (40000 ppm) is preferred.

When this B supply source solution is supplied from the surface of the green compact having an average porosity of 45%, and then dried by evaporating the solvent, the maximum density of 2000 ppm, preferably 10 to 1000 ppm, is converted into B inside the green compact. In the range of B, the B supply source remains.

In order to uniformly interpose the B supply source dissolved in the B supply source solution inside the green compact made of cemented carbide powder, the solvent is removed in the previous step of nitriding the green compact, and WC particles and bonding It is desirable to remove the oxide on the metal surface. This solvent removal step is desirably performed in a vacuum atmosphere at 1000 ° C. to 1200 ° C.

The cemented carbide according to the present invention manufactured through the manufacturing process as described above has a part or all of the WC particles constituting the WC-based cemented carbide sintered material formed by nitriding in a nitrogen-pressurized atmosphere. It has a double structure consisting of the WC nucleus and the surrounding structure of tungsten carbonitride. This cemented carbide can achieve further lower frictional performance.

Next, specific examples of the cemented carbide manufactured by the method of the present invention will be described.

[Example 1]
The cemented carbide of Example 1 is a metal powder obtained by weighing 91% by weight of WC powder having an average particle size of 1.5 μm and 9% by weight of Co powder having an average particle size of 1.1 μm. , Using a cemented carbide powder to which 0.1 wt% of B ₂ O ₃ powder as a B supply source is added in terms of B.

Commercially available powders of WC, Co, and B ₂ O ₃ are used here.

Cemented carbide powder mainly composed of WC and Co powder with B ₂ O ₃ powder added is put into a stainless steel pot together with ethanol solvent and cemented carbide ball, and mixed and ground in this pot for 30 hours. Is done. The cemented carbide powder mixed and ground in the pot is taken out from the pot and dried. Paraffin wax is added to the pulverized and dried cemented carbide powder. The cemented carbide powder to which paraffin wax is added is compression molded to a size of 10 × 10 × 5 (mm).

A green compact formed by compression molding cemented carbide powder is degreased at 600 ° C. in a hydrogen atmosphere, then heated from room temperature to 1390 ° C. in a vacuum atmosphere, and maintained at 1390 ° C. for 3.6 ksec. Is sintered. Thereafter, nitrogen gas was introduced into the furnace, the inside of the furnace was adjusted to 100 kPa, and the test piece was obtained. This test piece is a cemented carbide obtained by sintering a green compact obtained by compression molding cemented carbide powder. The 10 × 10 surface of the cemented carbide specimen prepared here was ground with a diamond grindstone, the surface layer was removed, and further mirror-finished with diamond paste.

The X-ray absorption spectroscopy (XANES) spectrum analysis was performed on the trace product of the test piece obtained here. For this analysis, an industrial beam line BL5 located at the University of Hyogo Prefectural University of New Zealand Synchrotron Radiation was used. The result is shown in FIG.

As is clear from FIG. 1, it was confirmed that h-BN was generated on the surface of the test piece prepared in Example 1. Further, when the incident angle of the radiated light on the test piece was changed to 45 ° C. and 90 ° C., the same intensity change as that of the h-BN standard sample was observed. From this result, it was confirmed that the h-BN produced on the surface of the test piece was oriented.

[Example 2]
Next, in the cemented carbide of Example 2, 91 wt% of WC powder having an average particle diameter of 6.0 μm and 9 wt% of Co powder having an average particle diameter of 1.1 μm were weighed. This powder is manufactured using a cemented carbide powder obtained by adding 0.1% by weight of B ₂ O ₃ powder as a B supply source in terms of B.

A cemented carbide powder mainly composed of WC and Co powders to which B ₂ O ₃ powder as a B supply source is added is made of stainless steel together with an ethanol solvent and a cemented carbide ball, as in Example 1 above. It is put into a pot and mixed and ground in this pot for 30 hours. The cemented carbide powder mixed and ground in the pot is taken out from the pot and dried. Paraffin wax is added to the dried cemented carbide powder. The cemented carbide powder to which paraffin wax is added is compression molded to a size of 30 × 25 × 13 (mm).

The green compact formed by compression molding the cemented carbide powder is degreased in a hydrogen atmosphere at 600 ° C., and then placed in a furnace that has a vacuum atmosphere and is heated from room temperature to 1100 ° C. The temperature inside the furnace is raised to 1390 ° C., and nitrogen gas is introduced into the furnace to adjust the inside of the furnace to 900 kpa to perform nitriding treatment of the green compact. The inside of the furnace into which the nitrogen gas has been introduced is maintained in a state where the temperature has been raised to 1390 ° C. for 3.6 ksec, whereby the green compact is sintered to form a sintered alloy. The sintered alloy sintered in the furnace is then cooled and used as a test piece. This test piece corresponds to a cemented carbide produced by sintering a green compact obtained by compression molding cemented carbide powder.

* The test piece obtained here is cut at the center. The cut surface of the cut specimen is ground with a diamond grindstone, then mirror-finished with diamond paste, and etched with Murakami reagent, which is a corrosive liquid that corrodes cemented carbide. The structure was observed using a scanning electron microscope. The observation results are shown in FIG.

The WC particles have a double structure of the WC nucleus and the surrounding tissue formed around it, as is apparent from the photograph in FIG. The surrounding tissue of the WC nucleus is presumed to be W (C, N).

[Examples 3 to 6, Comparative Example 1, Conventional Example]
Next, Examples 3 to 6 of the present invention, Comparative Example 1, and a conventional example are shown.

The cemented carbide of this Example 3 weighed 91% by weight of WC powder with an average particle size of 1.5 μm and 9% by weight of Co powder with an average particle size of 1.1 μm. The powder is produced from a cemented carbide powder obtained by adding 0.001 wt% of B ₂ O ₃ powder as a B supply source to the powder in terms of B.

The above cemented carbide powder is put into a stainless steel pot together with an ethanol solvent and a cemented carbide ball, and mixed and ground in this pot for 30 hours. The cemented carbide powder mixed and ground in the pot is taken out from the pot and dried. Paraffin wax is added to the dried cemented carbide powder. The cemented carbide powder to which the paraffin wax was added was compression molded to a size of 10 × 5 × 31 (mm). The compression-molded green compact is used as a bending strength test piece.

Moreover, the cemented carbide powder to which paraffin wax was added was compression molded to a size of 25 × 25 × 26.5 (mm). The compression-molded green compact is used as a friction coefficient measurement test piece.

Both the green compact used as the bending strength test piece and the green compact used as the friction coefficient measurement test piece were degreased in a hydrogen atmosphere at 600 ° C. and then put into a vacuum atmosphere furnace. The furnace is evacuated and the furnace temperature is raised from room temperature to 1390 ° C. and held at 1390 ° C. for 3.6 ksec for sintering. Thereafter, nitrogen gas is introduced into the furnace, and the inside of the furnace is adjusted to 100 kPa and cooled to produce a test piece as a sintered body subjected to nitriding treatment. This test piece is a cemented carbide produced by sintering a compact obtained by compression molding cemented carbide powder.

The cemented carbide of Example 4 was manufactured from cemented carbide powder obtained by adding 0.010 wt% of B ₂ O ₃ powder as a B supply source to the powder shown in Example 3 in terms of B. is there. The yield strength test piece and the friction coefficient measurement test piece obtained here are manufactured through the same manufacturing steps as in Example 3.

Further, in the cemented carbides of Examples 5 and 6, 0.100 wt% and 0.150 wt% of B ₂ O ₃ powder as a B supply source were added to the powder shown in Example 3 in terms of B, respectively. It is manufactured from the cemented carbide powder. The bending strength test piece and the friction coefficient measurement test piece obtained here are also manufactured through the same manufacturing process as in Example 3.

For comparison with the cemented carbides of Examples 3 to 6, as Comparative Example 1, WC powder with an average particle size of 1.5 μm was 91% by weight, and Co powder with an average particle size of 1.1 μm was 9 Friction strength test piece of cemented carbide made of cemented carbide powder obtained by adding 0.200% by weight of B ₂ O ₃ powder as a source to powder measured at a weight percent ratio and friction A coefficient measurement specimen was prepared.

For comparison with the cemented carbides of Examples 3 to 6 to which B ₂ O ₃ as a B supply source was added, 91 wt% of WC powder having an average particle size of 1.5 μm and an average particle size of 1 A bending strength test piece and a friction coefficient measurement test piece of cemented carbide manufactured from cemented carbide powder consisting only of a powder obtained by weighing Co powder of 1 μm at a ratio of 9% by weight were prepared. This is a conventional example.

The friction coefficient was measured using the friction coefficient measurement test pieces prepared in Examples 3 to 6 and Comparative Example 1 described above and the conventional example. The measurement of the friction coefficient was performed on the measurement surface of the friction coefficient measurement test piece subjected to mirror finishing. The friction coefficient measurement surface was subjected to grinding to remove the sintered surface, and further to the mirror finishing. Applied and formed.

The coefficient of friction measurement test piece was measured using a ball-on-plate method. In this ball-on-plate method, a φ10 mm aluminum sphere loaded with a load of 100 g is used as a test sphere, and the load generated by reciprocating the test sphere at an interval of 7 mm on the measurement surface of the friction coefficient measurement test piece is measured. Do it. The load is measured with a load cell attached to the test ball.

The measurement results are shown in FIG. As is apparent from the measurement results shown in FIG. 3, the B ₂ O ₃ addition amount as the B supply source was 0.001% by weight or more in terms of B, and thus the B supply source was not added. The friction coefficient was sufficiently reduced as compared with a cemented carbide made of a WC-based cemented carbide sintered material.

Further, the bending strength was measured using the bending strength test pieces prepared in Examples 3 to 6 described above and the bending strength test pieces prepared in Comparative Example 1 and the conventional example. The measurement results are shown in Table 1.

As is apparent from the measurement results shown in Table 1, the B supply source is added by setting the amount of B ₂ O ₃ added as the B supply source to 0.001 or more and less than 0.200% by weight in terms of B. A bending strength equivalent to that of a cemented carbide made of a sintered WC-based cemented carbide alloy was obtained.

In addition, like the cemented carbide of Comparative Example 1, when the amount of B ₂ O ₃ added as a B supply source was 0.200% by weight or more in terms of B, the bending strength was significantly reduced. This seems to be the result of precipitation of the η phase, which is a defect of the cemented carbide, when the amount of B ₂ O ₃ added is 0.200 wt% or more in terms of B.

Thus, the binding of the metal of the cemented carbide consisting of WC-based cemented carbide sintered _material, by the amount of addition of B 2 _{O 3} is added in less than 0.001 0.200 wt% in terms of B, binder phase A cemented carbide having a significantly reduced friction coefficient while achieving a bending strength equivalent to that of a conventional cemented carbide manufactured without adding B to the metal constituting the metal was obtained.

A cutting tool using this cemented carbide as a substrate, and further a cemented carbide tool including a die are excellent in low friction characteristics and can maintain a constant bending force.

[Examples 7 to 9, Comparative Example 2, Conventional Example]
Next, Examples 7 to 9 of the present invention, Comparative Example 2, and a conventional example are shown.

The cemented carbide of Example 7 was measured by measuring 91% by weight of WC powder having an average particle size of 1.5 μm and 9% by weight of Co powder having an average particle size of 1.1 μm. It is a cemented carbide produced from a cemented carbide powder obtained by adding 0.001 wt% of B ₂ O ₃ powder as a B supply source to the powder in terms of B.

The above cemented carbide powder is put into a stainless steel pot together with an ethanol solvent and a cemented carbide ball, and mixed and ground in this pot for 30 hours. The cemented carbide powder mixed and ground in the pot is taken out from the pot and dried. Paraffin wax is added to the dried cemented carbide powder. The cemented carbide powder to which paraffin wax is added is compression molded to a size of 10 × 5 × 31 (mm). The compression-molded green compact is used as a bending strength test piece.

Moreover, the cemented carbide powder to which paraffin wax was added was compression molded to a size of 25 × 25 × 26.5 (mm). The compression-molded green compact is used as a friction coefficient measurement test piece.

The green compact used as the bending strength test piece and the green compact used as the friction coefficient measurement test piece are both degreased in a hydrogen atmosphere at 600 ° C. and then placed in a furnace having a vacuum atmosphere. . The inside of the furnace in which the green compact is charged is evacuated and heated from room temperature to 1100 ° C. Thereafter, nitrogen gas is introduced into the furnace, the inside of the furnace is adjusted to 900 kPa, and the temperature is raised to 1390 ° C. And the green compact thrown into the furnace turns into a sintered test piece by hold | maintaining 3.6 ksec in the state heated up to 1390 degreeC, and then cooling. This test piece is a cemented carbide manufactured by sintering a green compact obtained by compression molding cemented carbide powder.

The cemented carbide of Example 8 was manufactured from cemented carbide powder obtained by adding 0.010 wt% of B ₂ O ₃ powder as a B supply source to the powder shown in Example 7 in terms of B. is there. The yield strength test piece and the friction coefficient measurement test piece obtained here are manufactured through the same manufacturing steps as in Example 7.

The cemented carbide of Example 9 was manufactured from cemented carbide powder obtained by adding 0.100 wt% of B ₂ O ₃ powder as a B supply source to the powder shown in Example 7 in terms of B. is there. The bending strength test piece and the friction coefficient measurement test piece obtained here are also manufactured through the same manufacturing process as in Example 7.

Here, in order to compare with the cemented carbides of Examples 7 to 9, as Comparative Example 2, 91% by weight of WC powder having an average particle diameter of 1.5 μm and Co having an average particle diameter of 1.1 μm were used. Bending strength of cemented carbide manufactured from cemented carbide powder obtained by adding 0.200% by weight of B ₂ O ₃ powder as a B source to powder measured at a rate of 9% by weight. A test piece and a friction coefficient measurement test piece were prepared.

The friction coefficient was measured using the friction coefficient measurement test pieces prepared in Examples 7 to 9 and Comparative Example 2 described above and the conventional example. The measurement of the friction coefficient was performed on the measurement surface of the friction coefficient measurement test piece subjected to mirror finishing, and the measurement surface of the friction coefficient was formed in the same manner as in the above-described Examples and Comparative Examples.

And the friction coefficient measurement of the friction coefficient measurement test piece also used the ball-on-plate method similarly to the above-mentioned Example. The measurement results are shown in FIG. As is apparent from the measurement results shown in FIG. 4, it was configured without adding the B supply source by containing 0.001 wt% or more of B ₂ O ₃ as the B supply source in terms of B. The friction coefficient was sufficiently reduced as compared with a cemented carbide made of a WC-based cemented carbide sintered material.

In particular, in order to manufacture the cemented carbide shown in Examples 7 to 9 and Comparative Example 2, a green compact obtained by compression molding cemented carbide powder was put into a furnace, and the furnace was heated to 1100 ° C. in a vacuum atmosphere. The adsorbed oxide adsorbed on the green compact is reduced. Thereafter, nitrogen gas is introduced into the furnace, adjusted to 900 kPa, heated to 1390 ° C., and held at 1390 ° C. for 3.6 ksec, whereby the green compact is sintered and a cemented carbide is produced. .

In the cemented carbide produced here, a part or all of the WC particles constituting the hard phase has a double structure of the WC nucleus and the surrounding structure of tungsten carbonitride. Therefore, further reduction in friction capability is achieved. From the comparison with the friction coefficients of the cemented carbides of Examples 3 to 6 shown in FIG. 3, it is apparent that the friction reduction of the cemented carbides of Examples 7 to 9 is realized.

Further, the bending strength was measured using the bending strength test pieces prepared in Examples 7 to 9 described above and the bending strength test pieces prepared in Comparative Example 2 and the conventional example. The measurement results are shown in Table 2. As is apparent from the measurement results shown in Table 2, the B supply source is added by setting the amount of B ₂ O ₃ added as the B supply source to 0.001 or more and less than 0.200% by weight in terms of B. A bending strength equivalent to that of a cemented carbide made of a sintered WC-based cemented carbide alloy was obtained.

In addition, like the cemented carbide of Comparative Example 2, when the amount of B ₂ O ₃ added as a B supply source was 0.200 wt% or more in terms of B, the bending strength was significantly reduced. This is considered to be a result of coarse h-BN larger than 1 μm being precipitated and resulting in structural defects when the amount of B ₂ O ₃ added is 0.200 wt% or more in terms of B.

As described above, in the same manner as in Examples 3 to 6 described above, the amount of B ₂ O ₃ added is 0.001 or more and less than 0.200% by weight in terms of B in the cemented carbide of WC. By doing so, it is possible to obtain a cemented carbide having a significantly reduced friction coefficient while realizing a bending strength equivalent to that of a cemented carbide prepared without adding B in the metal constituting the conventional binder phase. did it.

A cutting tool using this cemented carbide as a substrate, and further a cemented carbide tool including a die are excellent in low friction characteristics and can maintain a constant bending force.

The present invention has been described by taking as an example a cemented carbide made of a WC-based cemented carbide sintered material containing Co as a binding metal. Widely applied to WC-based cemented carbide sintered alloys in which h-BN is precipitated by nitriding the B supply source intervening between the grain boundaries formed between the WC particles constituting WC and the binding metal particles binding WC It can be made and is not limited to the above-described embodiments.

As described above, the cemented carbide tool using the cemented carbide according to the present invention has excellent lubricity and seizure resistance by imparting low friction reducing ability, reduces tool wear, By preventing seizure, it is useful to apply to plastic working such as forging and punching of soft materials such as various steels, copper alloys, and aluminum alloys as compared with conventional carbide tools. Moreover, the cemented carbide tool using the cemented carbide according to the present invention has excellent lubricity and seizure resistance even in cutting, and suppresses the occurrence of chipping, chipping, etc. by reducing the processing load, Since stable cutting performance can be exhibited over a long period of time, forging, punching and cutting apparatus can be improved in performance, labor saving and energy saving of these processes, and further cost reduction can be realized.

Claims (15)

1. In cemented carbide in which tungsten carbide particles are sintered and bonded with bonding metal,
   A cemented carbide characterized in that hexagonal boron nitride (h-BN) is dispersedly formed in a bonding metal that bonds the particles of tungsten carbide.
2. 2. The cemented carbide according to claim 1, wherein at least a part of the tungsten carbide particles has a double structure of a tungsten carbide nucleus and a tungsten carbonitride peripheral structure.
3. The hexagonal boron nitride (h-BN) formed in the bonding metal that bonds the particles of tungsten carbide is in the range of 10 to 1500 ppm in terms of boron (B). Cemented carbide.
4. The hexagonal boron nitride (h-BN) formed in the bonding metal that bonds the particles of tungsten carbide is in the range of 10 to 1000 ppm in terms of boron (B). Cemented carbide.
5. The hexagonal boron nitride (h-BN) formed in the bonding metal that bonds the particles of tungsten carbide is in the range of 10 to 500 ppm in terms of boron (B). Cemented carbide.
6. A cemented carbide tool, wherein the tool substrate is formed of the cemented carbide according to any one of claims 1 to 5.
7. A cemented carbide powder in which a boron (B) supply source is dispersed and mixed in a mixed powder obtained by mixing a tungsten carbide powder and a bonded metal powder that bonds between the tungsten carbide particles,
   Next, the cemented carbide powder is compression molded to form a green compact,
   Thereafter, the green compact is nitrided in a nitrogen-pressurized atmosphere, and hexagonal boron nitride (h-BN) crystal grains are dispersedly formed in a bonding metal that bonds the tungsten carbide particles. A method for producing a cemented carbide.
8. The green compact is heat-sintered in vacuum and then subjected to the nitriding treatment to disperse and form hexagonal boron nitride (h-BN) crystal grains in the bonding metal. Item 8. A method for producing a cemented carbide according to Item 7.
9. The method for producing a cemented carbide according to claim 8, wherein the step of nitriding the green compact is performed during the step of heating and sintering the green compact.
10. 8. The manufacture of cemented carbide according to claim 7, wherein the B supply source is one selected from the group consisting of B ₂ O ₃ , H ₃ BO ₃ , h-BN, WB and TiB _2. Method.
11. A cemented carbide powder prepared by mixing a tungsten carbide powder and a bonding metal powder that bonds the particles of the tungsten carbide is produced.
    Next, the cemented carbide powder is compression molded to form a green compact,
    Thereafter, a B supply source solution in which a B supply source is dissolved in a solvent is supplied from the surface of the green compact, and the B supply source is dispersedly supplied into the green compact.
    Next, the green compact is nitrided in a nitrogen-pressurized atmosphere, and hexagonal boron nitride (h-BN) crystal grains are dispersedly formed in a bonding metal that bonds the tungsten carbide particles. A method for producing a cemented carbide.
12. The method for producing a cemented carbide according to claim 11, wherein the B supply source solution is obtained by dissolving the B supply source in a solution at a ratio of 0.02 wt% to 4 wt% in terms of boron.
13. The method for producing a cemented carbide according to claim 11 or 12, wherein the B supply source uses B ₂ O ₃ or H ₃ BO ₃ that is soluble in a solvent.
14. The green compact is heat-sintered in vacuum and then subjected to the nitriding treatment to disperse and form hexagonal boron nitride (h-BN) crystal grains in the bonding metal. Item 12. A method for producing a cemented carbide according to Item 11.
15. 14. The method for producing a cemented carbide according to claim 13, wherein the step of nitriding the green compact is performed during the step of heating and sintering the green compact.

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