WO2018105706A1

WO2018105706A1 - Method for manufacturing fine free carbon dispersion type cemented carbide, cutting tip with exchangeable cutting edge, machined product formed from alloy, and method for manufacturing same

Info

Publication number: WO2018105706A1
Application number: PCT/JP2017/044080
Authority: WO
Inventors: 良彦土井
Original assignee: ユーゲル株式会社
Priority date: 2016-12-09
Filing date: 2017-12-07
Publication date: 2018-06-14
Also published as: US20190144973A1

Abstract

[Problem] The present invention relates to a cemented carbide and coated cemented carbide containing free carbon and addresses the problem of eliminating or reducing the demerits of free carbon even in a cemented carbide containing free carbon. Specifically, the present invention addresses the problem of providing a cemented carbide such that a decrease in strength can be suppressed by finely dispersing free carbon even when the free carbon is to be contained in the cemented carbide, and a beautiful mirror surface can be obtained as a mirror-finished surface because of the fine dispersion of free carbon in the cemented carbide. Also, the present invention addresses the problem of providing cutting tip with an exchangeable cutting edge and having high dimensional precision and a low-cost machined product of cemented carbide through the fine dispersion of free carbon. [Solution] The cemented carbide comprises tungsten carbide (WC), which has a carbon content in such a range that a liquid phase occurring under a high temperature does not contain any solid carbon, and cobalt (Co), and is characterized in that cavities caused by free carbon have a maximum diameter of 20 µm or less.

Description

Manufacturing method of fine free carbon dispersion type cemented carbide, cutting edge exchange cutting tip and processed product formed from the same alloy, and manufacturing method thereof

The present invention relates to a fine free carbon dispersion type cemented carbide, a coated cemented carbide, a processed product thereof, and a method for producing the same.
Specifically, (1) a method of manufacturing a cemented carbide containing free carbon, finely dispersing the free carbon (Free Carbon), minimizing strength reduction, and capable of mirror finishing; (2 ) It is possible to suppress the η phase generated at the boundary between the coating and the base metal in the CVD coated cemented carbide, and (3) Create a highly accurate sintered cemented carbide by dispersing fine free carbon. It is possible to create a high-accuracy cutting edge-replaceable cutting tip using cemented carbide or coated cemented carbide using this technology, and (4) processed products of cemented carbide can be processed by electrical discharge machining, grinding / polishing or after sintering. The present invention relates to machining by a cutting method or a combination of these methods, and the use of this cemented carbide makes it possible to produce a workpiece of cemented carbide at a low cost.

Conventionally, a cemented carbide in which tungsten carbide (WC) particles and cobalt (Co) as a binding metal are mixed and sintered at an appropriate ratio is known. There are many cases where a part of WC is replaced with carbides and nitrides such as TiC and TaC, carbides and carbonitrides combining these, depending on applications. Cemented carbide is used in many fields such as cutting tools and dies because of its high hardness and high strength.
Cemented carbide is produced by powder metallurgy using powder as a raw material. Accordingly, there is a risk that nests remain in the sintered cemented carbide, and it is always required to reduce the size and the number of the nests. This is because if there is a nest, the strength, hardness and the like are lowered and the performance as a cemented carbide alloy is deteriorated.
The nest is a fine hole or void that appears inside the cemented carbide structure and is also called “Pore” and is one of the material defects. The state of the nest is defined as “Porosity” in the cemented carbide association standard CIS006C-2007 “Porosity classification standard for superhard alloys”. In this rule, the nest types are classified into three types, A type, B type, and C type, and classified into four levels (grades) according to the size and number of nests, and the standard nest level is a 100-200 times microscope. Shown in the photo.
According to CIS006C, the size of the A-type nest is defined as 10 μm or less. The cause is considered to be a trace amount of gas and impurities (Non-patent Document 4, p. 176).
The size of the B-type nest is defined as 10 μm or more and 25 μm or less. The cause is considered to be Cо powder or impurities slightly larger than A type due to unpulverized lubricant (Non-Patent Document 4, p. 176).
The cause of C-type nests is considered to be due to the presence of free carbon, and the size is usually 25 μm or more (Non-patent Document 4, p. 176).

One of the most important issues in the quality control of cemented carbide is the proper control and control of the carbon content of the alloy. If the amount of carbon is large, free carbon remains in the alloy and nests are generated, resulting in a decrease in strength.
When observing the nest of free carbon with a 100 × microscope, small nests of nests gathered in a dendritic form to form one nest. Non-Patent Document 1 p. Fig. 66 of Fig. 66 shows a photograph observed at a high magnification of 500 times, and its dendritic shape can be seen more clearly.
The nest attributed to free carbon is C type in Appendix Table 4 of CIS standard 006C. Even in the C type 002 applied to the smallest nest of four stages, the size of the nest is about 70 μm at the largest. When such a large nest is generated, not only the strength is lowered but also a mirror surface defect is caused in the use of the mirror surface. For this reason, defective disposal loss and rework costs occur, or delivery time is delayed.
If the size of the free carbon nest can be reduced, the strength and hardness will not decrease, the quality of the mirror surface will be improved, and such loss can be avoided.
The inventor of the present application diligently researched and realized a cemented carbide and a cemented carbide manufacturing method in which the maximum diameter of the free carbon nest which has not been achieved so far is 20 μm or less.

Also, in the cemented carbide coated using the CVD method, an abnormal phase called η phase (decarburization phase) occurs at the boundary between the coating and the cemented carbide, causing the strength of the coated cemented carbide to decrease. (Non-Patent Document 3). In recent years, technical improvement has progressed and the η phase problem at the boundary between the coating and the base material has been reduced, but basically it is produced with a risk of η phase generation at all times.
Therefore, there is always a potential demand to suppress the generation of η phase. Cemented carbides are processed into tools and parts for many uses such as cutting and wear-resistant applications, but they are hard and difficult to machine. Electrical discharge machining and grinding / polishing with diamond wheels are mainly used. Yes. However, all of them are high-cost processing methods, and reduction of processing costs is a major issue. For this purpose, it is important to reduce the machining allowance by improving the dimensional accuracy of the cemented carbide sintered body.
Recently, the cutting of cemented carbide has become possible with the progress of diamond tools and diamond-coated tools in the cutting tool field. For abrasive tools such as dies, the development of technology for improving machining efficiency by cutting cemented carbide has been actively promoted in order to reduce machining costs and shorten delivery times. Therefore, the need for a cemented carbide with good machinability is increasing.
In addition, a cutting edge-exchangeable cutting tip, which is a main application of cemented carbide, requires a tip that has good cutting performance and at the same time can be used with a sintered surface having high dimensional accuracy. Since the dimensional accuracy of the blade tip replaceable cutting tip directly affects the dimensional accuracy of the product processed with the cutting tip, JIS and ISO determine the grade of the blade tip replaceable tip so that the user can easily select it. Of course, the higher the dimensional accuracy, the higher the price. A high-precision cutting edge replacement tip is produced by high-precision grinding. On the other hand, there is a strong demand for non-grinding (inexpensive molds that are not ground or only partially ground), and the amount of use is increasing, and there is a development race to improve the dimensional accuracy of non-grinding blade-tip inserts. It has been broken. The present invention meets these needs.

Patent Documents 4, 5, 6, and 7 are available for cemented carbide containing free carbon.
Patent Document 4 relates to a cemented carbide having a large amount of carbon and having solid carbon in a liquid phase, and is in a region corresponding to 0.15 to 0.17% or more in terms of free carbon. On the other hand, the present invention relates to a cemented carbide in a region in which solid carbon does not exist in a liquid phase state, that is, a region having less free carbon (see FIG. 1).
Further, in claim 1 of Patent Document 4, the amount of free carbon contained is 1.1% to 8% in terms of cross-sectional area. On the other hand, in the present invention, free carbon is 0.15% or less by weight. Free carbon has a specific gravity smaller than that of a WC / Co-based cemented carbide, so it is about 0.6% in volume%, and the present invention relates to a region outside the scope of Patent Document 4.
Patent Document 5 is characterized in that the cemented carbide has a double structure and the amount of free carbon in the inner and outer peripheral portions is different, and the size of the free carbon is not reduced.
Patent Document 6 relates to a special cemented carbide relating to a discharge electrode having a small diameter with limited use. Both the material evaluation method and the performance evaluation method of cemented carbide are limited to this application.
In Patent Document 7, in order to improve the quality of the CVD-coated cemented carbide, the cemented carbide has a double structure and a layer containing free carbon is formed outside, and the size of the free carbon is not controlled. Absent.

Japanese Patent No. 5826138 Japanese Patent No. 4673189 JP 2009-035802 A JP 2005-271093 A Japanese Patent No. 5978671 Japanese Patent No. 4535493 Japanese Patent Publication No.62-023041

There are roughly two problems to be solved by the present invention. One is to improve product yield. That is, it is to produce a cemented carbide that does not decrease strength even in a state in which free carbon is finely dispersed to contain free carbon.
The other is to provide high performance products for applications that take advantage of free carbon-containing alloys. That is, as will be described later, a cemented carbide sintered body with high dimensional accuracy is manufactured, a high-precision and high-performance tip replacement type chip is provided, and a cemented carbide alloy processed product that can be processed efficiently and at a low processing cost. Is to provide.
Specific examples will be described below along the objects and problems of the present invention.

The first object of the present invention is to reduce the nest of free carbon. This can improve yield reduction and delivery delay.
In the production process of cemented carbide, if carbon is not properly adjusted and free carbon is contained after sintering, the strength is reduced (Non-patent Document 1 p.95, Fig. 1.115), and the mirror-finished surface is caused by free carbon. The nest is observed and problems such as the inability to obtain a beautiful mirror surface have occurred.
The degree of free carbon generation in cemented carbide is classified according to the standard photograph (Non-Patent Document 2) in Fig. 4 of the cemented carbide tool association standard CIS006C-2007 "Cemented carbide porosity classification standard". From C02 to C08. When free carbon is produced in a generally produced cemented carbide, it becomes as shown in FIG. 4, and the free carbon (nest) has the smallest C002 to the largest C008. When the size of free carbon is judged from these photographs in FIG. 4, the maximum diameter of the nest due to free carbon of C002 is about 70 μm. In C006, the maximum diameter is 100 μm or more. As shown in the photograph of Fig. 4 of free carbon, the shape of the nest of free carbon is a small nest with several small spots gathered into a single nest. The size of this aggregate was measured as the nest size.
And such free carbon becomes a starting point of destruction and reduces strength. Moreover, when finished to a mirror surface, free carbon is observed as a kind of nest and does not become a beautiful mirror surface. For the above-mentioned reasons, cemented carbides with free carbon are generally inferior due to quality problems, require rework and remanufacturing, and ultimately lead to yield reduction and delivery delay.
Therefore, in the present invention, the free carbon in the cemented carbide is finely dispersed so that the maximum diameter of the nest in the cemented carbide is 20 μm or less, preferably 15 μm or less, more preferably 10 μm or less, and the strength is reduced. By providing a cemented carbide and a method for producing a cemented carbide capable of suppressing and obtaining a beautiful mirror surface even on a mirror-finished surface, it is possible to improve yield reduction and delivery delay.

The second object of the present invention is to provide a more stable base material for CVD coated cemented carbide.
Although the coated cemented carbide by CVD method is prevalent today, TiC, TiCN, TiN are generally used as the coating in contact with the cemented carbide. These Ti compounds absorb carbon in the cemented carbide and tend to generate a decarburized η phase at the boundary between the coating and the cemented carbide. The η phase reduces the strength of the coated cemented carbide (Non-Patent Document 5 and Patent Document 7). However, it has been found that a cemented carbide containing free carbon can suppress the generation of η phase because it contains excessive carbon (Non-patent Document 3).
Therefore, in the present invention, by providing a cemented carbide containing free carbon and having no strength reduction as a base material for CVD coated cemented carbide, it is possible to provide a coated cemented carbide that suppresses the generation of η phase. It becomes possible.

A third object of the present invention is to provide a free carbon finely dispersed cemented carbide and a coated cemented carbide having further improved performance in practical use.
In the presence of free carbon, the lattice constant of fcc of the bonded phase (Co phase) is constant at about 3.550Å (Non-patent Document 1 p99 and FIG. 1.115 on the same page). Increasing the amount of tungsten (W) dissolved in Cо and increasing the lattice constant is expected to improve heat resistance and improve cutting performance. However, there is no report that the lattice constant could be increased in the presence of free carbon.
In the present invention, it is possible to produce a material having a lattice constant of 3.560 mm or more by rapidly cooling from the liquid phase state to 800 ° C. Cutting performance was equal to or better than cemented carbide without free carbon. The cutting performance was also improved in the coated cemented carbide using the cemented carbide as a base material.
A cemented carbide in which free carbon, which will be described later, is dispersed can also improve the dimensional accuracy. The present invention also makes it possible to provide a cutting edge replaceable cutting tip with good cutting performance and high dimensional accuracy.

A fourth object of the present invention is to provide a cutting edge replaceable cutting tip with high dimensional accuracy.
Cemented carbide is made by pressing the mixed powder and sintering the pressed body, but shrinks by about 50% (about 20% in size) by volume when the pressed body becomes a sintered body. Estimate the shrinkage rate, make a pressed body, and make a sintered body of the desired dimensions. If the weight and volume of the plurality of pressed bodies are the same, the volume of each sintered body can be made the same, but the dimensions change. This is because even if the volume of the sintered body is the same, the shrinkage does not have a similar shape, and distorts and dimensional variations occur. Moreover, even if a plurality of the same items are created, differences between individuals occur.
One of the major factors for the damage is the slight variation in the carbon content inside the sintered body. This variation in carbon occurs due to various factors, such as absorption of moisture from the surface of the pressed body, influence of the atmosphere in the sintering furnace, and the like. The melting point on the low carbon side is 1357 ° C., the melting point on the high carbon side (the side on which free carbon exists) is 1298 ° C., and when the temperature rises for sintering, the high carbon side with the low melting point starts to shrink quickly. However, the low carbon side having a high melting point contracts with a delay. In this way, the sintered body is damaged. Even if the amount of carbon in the press partially varies, the melting point does not change as long as free carbon is present, and therefore shrinkage occurs evenly.
That is, when the pressed body is converted into a sintered body, it shrinks by about 50% by volume, but the normal one in which free carbon is not dispersed does not shrink in a similar shape, and it becomes distorted, but the one containing dispersed free carbon is similar. The shape shrinks and there is no damage. Therefore, the cemented carbide in which free carbon is finely dispersed becomes a sintered body with high dimensional accuracy.
In many cases, the blade-tip-exchangeable cutting tip has a complicated shape formed on the upper surface of the tip with a mold, but it is industrially difficult to grind after sintering. Further, the dimensional variation of the tip of the tip determines the dimensional accuracy of the product processed with the tip, and it is always required that the dimensional variation of the tip is small. In addition, high-precision chips are also produced by grinding the side surfaces of the chips, but this requires processing costs. Recently, all or part of the side surfaces are not ground and sintered (sintered). Therefore, it is necessary to improve the dimensional accuracy of the sintered body.
The present invention provides a blade-tip-exchangeable cutting tip having such high dimensional accuracy. Further, in a rolling tool in which a plurality of tips are attached to a rotating body and used, variation in the dimensional accuracy of the tips is even more important. That is, in a milling tool which is one of representative examples of a rolling tool, a plurality of inserts are incorporated and used as a single unit. If the dimensional variation is large, the variation in wear between the chips is increased, and the life of the milling tool is shortened. In this cutting application, PVD-coated cutting edge exchangeable cutting tips are frequently used. Even with PVD coating, high accuracy is maintained and does not change. In turning applications, CVD-coated cutting edge-exchangeable cutting tips are frequently used, but high dimensional accuracy is maintained even when CVD-coated.

The fifth object of the present invention is to provide a cemented carbide processed product with a low processing cost.
Cemented carbide is used in a wide range of cutting tools, various molds, anti-wear tools such as dies, civil engineering and mining tools, and performance improvement according to various applications is promoted day and night.
On the other hand, cemented carbide is known as an extremely hard and difficult-to-machine material, and electric discharge machining and grinding / polishing with a diamond grindstone are mainly used for the machining. Both are expensive processing methods. Recently, cutting tools have also progressed, and tools using sintered diamond and diamond-coated tools have progressed, making it possible to cut some cemented carbides and improving the machining efficiency of cemented carbides. Cutting is a cheaper and more efficient machining method than electric discharge machining or grinding. However, cutting of difficult-to-cut materials such as cemented carbide has a short tool life and a long machining time.
Since the cemented carbide of the present invention contains free carbon, it has the property of having a low melting point. It is known that the melting point is lowered when free carbon is contained (Non-patent Document 1, p. 96), and the melting point of the alloy containing free carbon is 1298 ° C., and the melting point on the low carbon side is 1357 ° C.
Thus, since the cemented carbide of the present invention has a lower melting point than cemented carbide containing no free carbon, it is presumed that the machinability is good. Actually, it was demonstrated in Example 6. Although the machinability is largely governed by other properties of the cemented carbide such as the grain size and the amount of C0, the present invention can provide a cemented carbide with good machinability with the same composition.
In addition, it is known that a cemented carbide containing free carbon has a low melting point as well as a low electrical resistance (Non-patent Document 1 p.63). In the hard alloy, the specific resistance on the low carbon side is about 23 μΩcm, and the specific resistance of the cemented carbide containing free carbon is 17.8 μΩcm. Therefore, improvement of electric discharge machining can be expected.
The demand for improving the dimensional accuracy is not limited to the cutting edge-exchangeable cutting tip described for the fourth purpose. Processed products of cemented carbide such as molds are processed from sintered products to finished molds by electrical discharge machining, cutting, grinding / polishing, etc. However, if the dimensional accuracy is poor due to damage etc., the machining allowance increases. The processing time is long, and the wear of tools such as cutting tools and grinding wheels is also high, which is expensive. If the amount of damage is reduced, the machining time is shortened and the wear of the tool is reduced, so that the machining cost can be reduced.

The sixth object of the present invention is to make use of the cemented carbide for other applications that are difficult to put into practical use due to defects and problems caused by containing free carbon.
For example, providing a cemented carbide with a low coefficient of friction. If free carbon is present in the cemented carbide, a good mirror surface cannot be obtained, and it has not been put into practical use at present. However, since the mirror surface is obtained by finely dispersing free carbon in the cemented carbide, it is possible to provide a cemented carbide having improved lubricity by utilizing the lubricity of free carbon. Other application developments are also expected in the future.

In view of such problems, the main object of the present invention is (1) a cemented carbide containing free carbon, a coated cemented carbide, a processed product thereof, and a method for producing the same, and a cemented carbide containing free carbon. However, it is to eliminate or reduce the disadvantages of the free carbon. Specifically, even if free carbide is contained in the cemented carbide, the decrease in strength is suppressed by finely dispersing the free carbon. Another object of the present invention is to provide a cemented carbide and a method for producing a cemented carbide capable of obtaining a fine mirror surface even in a mirror-finished surface by finely dispersing free carbon in the cemented carbide.
In addition, an object of the present invention is to provide a high performance cemented carbide that can take advantage of free carbon contained in the cemented carbide, and object (2) is to provide finely dispersed free carbon. It is to provide a CVD-coated cemented carbide that suppresses the generation of η phase by providing the contained cemented carbide as a base material for a CVD-coated cemented carbide. The purpose (3) is to produce a cemented carbide sintered body with high dimensional accuracy, and to provide a cutting edge replaceable cutting tip with good cutting performance and high dimensional accuracy. The purpose (4) is to develop a cemented carbide with high dimensional accuracy and good workability, and to provide a cemented carbide product that can be processed in a shorter time and at a lower processing cost.

The present invention is a cemented carbide comprising tungsten carbide (WC) and cobalt (Cо) containing carbon in a range that does not contain solid carbon in the liquid phase at high temperatures, and is caused by free carbon. The maximum diameter of the nest is 20 μm or less.
In the cemented carbide comprising tungsten carbide (WC) and cobalt (Cо) containing finely dispersed free carbon, the present invention contains 0.02% to 0.15% of free carbon. The maximum diameter of the nest caused by free carbon is 20 μm or less.
More preferably, the cemented carbide of the present invention is characterized in that the maximum nest diameter caused by free carbon is 15 μm or less.
More preferably, the cemented carbide of the present invention is characterized in that the maximum nest diameter caused by free carbon is 10 μm or less.
According to Fig. 1 (Non-Patent Document 1, p. 96, Fig. 1.112 (b)), when the free carbon is about 0.15% to 0.17% or more, the liquid phase appears (about 1298 ° C or more). In this case, free carbon exists as a solid, and the free carbon continues to exist when the liquid phase is solidified by cooling. This region has excessive free carbon and is not generally used as a cemented carbide. If the liquid phase appears at 0.01% or more and 0.15% or less, all the carbon is dissolved in the liquid, and free carbon is precipitated from the liquid phase when solidified. The present invention aims to reduce the size of the free carbon. Details are also described in <Method of making free carbon finer>.
In addition, free carbon is not set to 0.01% or more, and 0.02% or more is reduced to 0.01% or less in which both the number and size of nests caused by free carbon are reduced, and defects due to free carbon are also apparent. This is because there are many cases where it does not.

The degree of free carbon generation in cemented carbide is classified into C type nests according to CIS006C-2007 “Cemented carbide porosity classification standard”, and the degree is determined by C02 to C08 in Figure 4 (Non-Patent Document 2). When free carbon is generated in a cemented carbide that is normally produced, it becomes a C-type nest in FIG. Depending on the number of nests of free carbon, it is classified from C002 with the smallest nest to C008 with many nests. If the diameter of free carbon is judged from these photographs in FIG. 4, even C002 with a small nest contains about 25 μm to 70 μm.
As shown in the photograph in Fig. 4, the shape of the free carbon nest is a small nest with several small points gathered into a single nest, and the size of this aggregate was measured as the size of the nest. And such a nest (free carbon) becomes a starting point of destruction and reduces strength (Non-patent Document 1, p. 99, Fig. 1.115). Also, when finished to a mirror surface, free carbon is observed as a kind of nest, so it does not become a beautiful mirror surface. When the size (maximum diameter) of the free carbon nest is dispersed to 20 μm or less, the nest becomes almost invisible to the naked eye. Therefore, the problem of the mirror surface is improved or eliminated, the strength is also improved, and it approaches or is almost equivalent to that not containing free carbon.
The inventor of the present application sinters mixed powder for producing cemented carbide and rapidly cools it from the liquid phase existence state at cooling rates of 30 ° C./min, 50 ° C./min, and 70 ° C./min. The present invention has invented a cemented carbide and a method for producing a cemented carbide in which the maximum diameter of the free carbon nest that has not been reached is 20 μm or less, 15 μm or less, or 10 μm or less.

According to the present invention, by further reducing the nest size (maximum diameter) of free carbon to 15 μm or less, the strength (bending strength), hardness, and mirror surface quality are further improved as compared to the case where the maximum nest diameter is 20 μm A cemented carbide is provided.

According to the present invention, by further reducing the nest size (maximum diameter) of free carbon to 10 μm or less, the strength (bending strength), hardness and mirror surface quality are further improved as compared with the case where the maximum nest diameter is 20 μm. A cemented carbide is provided.

The cemented carbide of the present invention is characterized in that chromium carbide or chromium nitride of 2 to 18% of the amount of cobalt (Cо) is added.
According to the present invention, even in a cemented carbide to which chromium carbide or chromium nitride is added, if free carbon is finely dispersed, the strength and hardness can be made substantially the same as that of a cemented carbide having no free carbon.
It is said that when chromium (Cr) is dissolved, the compressive strength, heat resistance strength and fatigue strength of the cemented carbide are improved (Patent Document 1). However, if it is 2% or less with respect to the amount of cobalt (Co), there is no effect, and if it is 18% or more, crystals of chromium carbide precipitate and there is a risk of reducing the strength of the cemented carbide. Therefore, the appropriate range is 2 to 18%.

In the cemented carbide of the present invention, a part of tungsten carbide (WC) is a transition metal carbide (excluding W), nitrides, carbonitrides, W, and W in the periodic table 4, 5, 6 elements. It is characterized in that it is replaced with any one of a transition metal carbide, nitride, double carbide with carbonitride, double carbonitride, or a combination thereof.
According to the present invention, a part of tungsten carbide (WC) is a transition metal carbide (except for W), nitrides, carbonitrides, W and the transition metals of Group 4, 5 and 6 elements of the periodic table. Even in a cemented carbide in which any one of carbides, nitrides, double carbides with carbonitrides, double carbonitrides or a combination thereof is replaced, the free carbon is finely dispersed, and the strength and hardness of the free carbon It can be almost equivalent to the one without a nest.

The present invention is characterized in that a de-β layer is formed on the surface of the cemented carbide, and the thickness of the de-β layer is 1 to 30 μm.
Here, the β-free layer is a layer having no β phase, and is a layer having a high Co content and a slightly low hardness but excellent strength and toughness.
The cemented carbide of the present invention is used as a base material for CVD coating. According to the present invention, a nitrogen compound such as TiN or TiCN is added to a cemented carbide containing a β phase to form a deβ layer. By forming, it becomes possible to reinforce the brittleness of the coating film, and it can be suitably used as a base material for CVD coating.
Since the purpose of the de-β layer is to reinforce the brittleness of the coating film, the effect is insufficient at 1 μm or less, and when it is 30 μm or more, the tool edge is used when the cemented carbide of the present invention is used as the tool edge. Tool performance decreases due to insufficient high-temperature hardness.

The present invention is characterized in that a fcc lattice constant of the bonded phase (Co phase) of the cemented carbide is 3.560 or more.
ADVANTAGE OF THE INVENTION According to this invention, the cemented carbide and covering cemented carbide which improved cutting performance can be provided because the lattice constant of fcc of a binder phase (Co phase) shall be 3.560 or more.
A cemented carbide with a high lattice constant is said to have high heat resistance, improved fatigue strength, and improved cutting performance. In addition, it is said that there is an improvement in performance even with wear-resistant tools (Patent Document 1, Patent Document 2). The cemented carbide containing free carbon has the lowest lattice constant of about 3.550% (Non-patent Document 1, P99 and Fig. 1.115 on the same page).
In order to finely disperse the free carbon, in the manufacturing process of manufacturing a cemented carbide, the mixed powder for producing the cemented carbide is rapidly cooled from the liquid phase existing state after sintering. Keep cooling rapidly. It was found that due to this rapid cooling effect, solid solution of tungsten (W) into the Co phase progresses even in the presence of free carbon, and the lattice constant increases. Although there was no big difference in the bending strength and hardness, the performance was improved by the cutting test. It is thought that there is a difference in performance other than cutting applications such as for abrasion resistance.
The inventor of the present application included free carbon having a lattice constant of 3.560 Å or more, which could not be achieved in the past, by finely dispersing free carbon in the cemented carbide even if free carbon is contained in the cemented carbide. Invented cemented carbide.
The effect of the lattice constant continued on the coated cemented carbide based on this cemented carbide and the cutting performance was improved. As described later, the free carbon dispersion type cemented carbide has high dimensional accuracy. The present invention is a cemented carbide or coated cemented carbide in which free carbon is finely dispersed, the dimensional accuracy is high, and the lattice constant of the fcc of the binder phase (Co phase) is 3.560 mm or more, and a cutting edge exchange type cutting made of these. It is characterized by providing a chip.

The cemented carbide of the present invention is used as a base material for a coated cemented carbide.
Although a coated cemented carbide by CVD method is widely used, TiC, TiCN, and TiN are generally used as the coating in contact with the cemented carbide. These Ti compounds absorb carbon in the cemented carbide and tend to generate the η phase of the decarburized layer at the boundary between the coating and the cemented carbide. The η phase reduces the strength of the coated cemented carbide (Non-patent Document 5, Patent Document 7). However, the cemented carbide containing free carbon contains excessive carbon and can suppress the generation of η phase (Non-patent Documents 3 and 7).
By using the cemented carbide of the present invention as a base material for a coated cemented carbide, a coated cemented carbide having improved strength with few η phases at the boundary is provided.

The cemented carbide or coated cemented carbide of the present invention is used as a cutting edge exchangeable cutting tip.
Further, by using the cemented carbide or the coated cemented carbide of the present invention, it is used as a processed product such as a tool, a mold, or a part.
According to the present invention, it is possible to manufacture cemented carbide and coated cemented carbide with improved dimensional accuracy. The present invention is characterized in that it is possible to provide a cutting edge-replaceable cutting tip that eliminates or reduces grinding by improving the dimensional accuracy.
Further, the cemented carbide of the present invention has a high dimensional accuracy, so there is little machining allowance and good workability, so that the machining cost can be reduced. Therefore, using the cemented carbide of the present invention, it is possible to provide a cemented cemented carbide processed product such as a tool, a die, or a component, or a coated cemented carbide alloy at a lower cost.

The manufacturing method of the cemented carbide according to the present invention is such that when producing a fine free carbon dispersion type cemented carbide, the mixed powder for producing the cemented carbide is sintered at a sintering temperature equal to or higher than the liquid phase appearance temperature, and then the liquid phase appears. It is characterized by having a step of quenching from a temperature higher than the temperature or a step of reheating to a temperature higher than the appearance of the liquid phase and quenching.
The method for producing a cemented carbide according to the present invention is characterized in that the cooling rate in the rapid cooling step and the reheating and rapid cooling step is 30 ° C./min or more.
Here, the “step of rapidly cooling from the temperature above the liquid phase appearance temperature” refers to a step of rapidly cooling the cemented carbide from the temperature above the liquid phase appearance temperature. “Strong cooling” and “Strong cooling” are also included.
The “reheating and quenching process” is a process in which the sintered cemented carbide is again heated to a temperature above the liquid phase appearance temperature and rapidly cooled. "Heating rapid cooling" and "reheating strong rapid cooling" are also included.
The mixed powder blended so that free carbon was present was pressed and sintered. At that time, in order to finely disperse the free carbon, it was rapidly cooled from the liquid phase. The cooling rate from the liquid phase to 800 ° C. is usually about 10 ° C./min. In this case, the C type nest of CIS006C-2007 “Cemented carbide porosity classification standard” is used. Present in cemented carbide.
Sintered using the same mixed powder and cooled at a cooling rate of 20 ° C./min and 30 ° C./min from the liquid phase presence state. Cooling at 20 ° C./min is super hard than cooling at 10 ° C./min. There were fewer nests with a diameter of 20 μm or more in the alloy, but they remained. When cooled at 30 ° C./min, there was no nest having a diameter of 20 μm or more.
Therefore, the cooling rate was set to 30 ° C./min or more. Further, when the cooling rate is increased, the nest diameter is reduced. In the trial experiment, when the cooling rate was about 50 ° C./min, the nest having a diameter of 15 μm or more disappeared, and when the cooling rate was 70 ° C./min or more, the nest having a diameter of 10 μm or more disappeared.
According to the present invention, after sintering the mixed powder for producing a cemented carbide alloy at a sintering temperature equal to or higher than the liquid phase appearance temperature, quenching by rapid cooling or reheating, and increasing its cooling rate, It is possible to disperse the nest in the hard alloy and reduce the nest diameter.

In the method for producing a cemented carbide according to the present invention, the cemented carbide produced by the above production method does not contain 1% or more of molybdenum (Mо).
Further, in the cutting edge-exchangeable cutting tip or the cemented carbide processed product of the present invention, the cemented carbide to be used does not contain 1% or more of molybdenum (Mо).
When molybdenum (Mо) is contained, molybdenum carbide, molybdenum / tungsten double carbide, and free carbon are precipitated when the cemented carbide is produced. Further, since the liquid phase appearance temperature is different, the present invention is limited to the WC-Cо alloy system not containing molybdenum (Mо). The reason why the amount of molybdenum (Mо) contained is set to 1% or less is that a small amount of molybdenum (Mо) may be present as an impurity. Because there is no.

According to the present invention, the maximum diameter of the nest in the cemented carbide is set to 20 μm or less, preferably 15 μm or less, more preferably 10 μm or less by finely dispersing free carbon in the cemented carbide to suppress a decrease in strength. In addition, by providing a cemented carbide and a method for producing a cemented carbide capable of obtaining a clean mirror surface even on a mirror-finished surface, yield reduction and delivery delay can be improved.
In addition, according to the present invention, by providing a cemented carbide containing free carbon as a base material for a CVD coated cemented carbide, it is possible to provide a coated cemented carbide that suppresses the generation of η phase and has a stable strength. It becomes possible.
According to the present invention, the free carbon is finely dispersed in the cemented carbide to eliminate the defect of the nest caused by the free carbon and to eliminate or reduce the cutting process with high dimensional accuracy. Can be provided. If the dimensional accuracy of the cutting tip is improved, the dimensional accuracy of the machined product is also improved. In a rolling application in which a plurality of inserts are used integrally, if the dimensional variation is poor, a protruding cutting edge is generated, and the cutting edge is quickly worn out. As a result, the life of the cutting tool is shortened. That is, the fine free carbon dispersion type cutting edge exchangeable tip can be used as a cutting tool that is inexpensive, has high dimensional accuracy, and has a long life.
Furthermore, according to the present invention, free carbon is finely dispersed in the cemented carbide, so that it is possible to provide a cemented carbide with high dimensional accuracy and low machining allowance after eliminating the defects of the free carbon nest. Become. If the machining allowance is small, machining such as electric discharge machining, grinding / polishing, and cutting will be performed in a short time, and the wear of the machining tool will be reduced, thereby greatly improving machining efficiency.
In addition, the machining of cemented carbide has traditionally been electrical discharge machining and grinding, but recently a cutting method capable of significant efficient machining has been developed and is beginning to spread. The fine free carbon dispersion type cemented carbide is easier to cut than the conventional cemented carbide. Thus, not only the machining allowance is small, but also the machinability is good and the electric discharge machinability is good, so that it is possible to provide a cemented carbide processed product with a low machining cost.

WC-Co pseudo binary system vertical cross section (Suzuki Suzuki, “Cemented carbide and sintered hard material”, Maruzen (1986), p. 96, reprinted in Fig. 1.112 (b))

<Definition of nest size caused by free carbon and its measurement method>
The degree of generation of free carbon in the cemented carbide is determined by C02-C08 in FIG. 4 of CIS006C, the quality standard of the cemented carbide tool association. When free carbon is produced in a cemented carbide that is normally produced, the result is as shown in FIG. Although C002 has the smallest free carbon and C002 has the smallest free carbon, the maximum diameter is about 70 μm even in C002 with the smallest free carbon. When the free carbon nest shown in the photograph of Fig. 4 is seen, the shape of the nest of the free carbon is a small nest in a dendritic shape, and the size of this aggregate was measured as the nest size. The nest of free carbon is generally 25 μm or more (Non-patent Document 4, p283-284).
In the present invention, the size of the free carbon nest was measured by polishing a test sample by the method described in CIS006C and observing with a 100 × microscope as in FIG. 4 with CIS006. Also, if there are no nests caused by free carbon of 20 μm or more for two fields of view (about 0.07 × 0.1 mm) in the same size as the figure, or 10 fields are arbitrarily observed and 20 μm in 7 fields The case where there is no nest attributed to the above free carbon was determined to be a cemented carbide with a maximum diameter of the nest attributed to the free carbon of 20 μm or less. The same measurement method was used for cemented carbide having a maximum nest of 15 μm and 10 μm or less due to free carbon.
However, as a precaution, even if the nest originates from free carbon, it may be difficult to distinguish it from the A-shaped nest when the nest is smaller than 20 μm. In order to confirm that it is caused by free carbon, as described in paragraph 0003, it is also necessary to observe and confirm at a high magnification of several hundred times or more. In addition, since chemical analysis (% free carbon) is performed as shown in Tables 2, 4, 6, 7, 8, and 9 of the examples in parallel, if there is free carbon, it is confirmed that the nest is caused by free carbon. it can.

<Method to refine free carbon>
1 is a vertical sectional view of a WC-Co pseudo-binary system (Suzuki Suzuki (1986) “Cemented Carbide and Sintered Hard Material” Maruzen, p. 96, reprinted in FIG. 1.112 (b)).
There are two types of precipitation of free carbon in cemented carbide. According to FIG.
(1) When the carbon content of the cemented carbide is 6.3% or more in terms of WC, when the liquid phase appears, WC + liquid (L) + carbon (C). When cooled to a solid with this composition, WC + γ + C is obtained.
(2) When the carbon content is 6.13% or more and 6.3% or less in terms of WC, the liquid phase appears as WC + liquid (L), but when cooled with this composition, it becomes WC + γ + C. Since the theoretical carbon content of WC is 6.13%, it is 0.01 to 0.17% in terms of free carbon.
Here, γ is a bonded phase (usually referred to as Cо phase) whose main component is Cо of the crystal structure fcc. The present invention is applied only to the case (2). In the case of (1), carbon in the liquid phase remains as it is when the solid phase appears, and excessive free carbon exists, and this region is not usually used as a cemented carbide. However, Patent Document 4 relates to the area (1) and was developed for a special purpose.
In the case of (2), free carbon (C-shaped nest) is precipitated from the liquid phase when the liquid phase is changed to a solid phase having a melting point or lower. The cemented carbide of the present invention can be realized by dispersing the precipitated free carbon in a small size. Specifically, in order to disperse the free carbon precipitates in a small amount, the liquid phase is quenched.
In theory, the faster the free carbon, the finer the free carbon. However, if the cooling rate is too fast, internal stress may remain or furnace deterioration may occur depending on the product. Therefore, there is a limit according to the actual situation.
The size of free carbon is not only influenced by the amount of free carbon present in the cemented carbide, but also affected by the composition and the shape and size of the sintered body.
Therefore, it is desirable to select the optimal cooling rate according to the actual situation in advance. In terms of equipment, gas quenching technology has evolved and 100 ° C./min is sufficiently possible, and examples of 1000 ° C./min and 10,000 ° C./min have been reported (Patent Documents 2 and 3). Normally, free carbon becomes a C-shaped nest when examined at 100 times magnification based on CIS006C, but it may appear as A-shaped when finely dispersed. Therefore, as described in paragraph 0003, there is also a method of confirming by observing at a high magnification of several hundred times or more as described in paragraph 0003 in order to confirm that it is caused by free carbon. It can also be confirmed by chemical analysis (% free carbon) as shown in Tables 2, 4, 6, 7, 8, and 9 in the Examples.

<Cooling method>
A vacuum furnace is usually used for sintering and reheating. Recently, many of these vacuum furnaces are equipped with a device capable of performing forced cooling with an inert gas. It is convenient to use this kind of vacuum furnace for production. If the amount of gas is increased or the gas pressure is increased, the cooling rate can be increased, and the cooling rate can be controlled according to the actual situation. When a large furnace is charged with a large amount of cemented carbide (product), the gas amount and gas pressure are increased. When the charged amount is small and the product shape is small, the gas amount and gas pressure may be small. The inert gas can be Ar or N2 gas. N2 has a slightly larger cooling effect than Ar, and is industrially advantageous in terms of cost.

Hereinafter, the best mode for carrying out the present invention will be described based on examples. It should be noted that the present invention is not limited to the following embodiments, and known modifications can be made within a range substantially the same as or equivalent to the present invention.

Example 1
Examples of WC-Cо materials are described below.
The mixed powder before sintering was prepared by mixing with the composition of (Table 1) using a commercially available raw material, mixing with a wet ball mill by a general method using alcohol, and drying. A with Cr3C2 added was designated as A, and B with no added Cr3C2. A2 and B2 had a carbon blending amount of 0.14% greater than A1 and B1, and B4 and B5 had a carbon blending amount of 0.10% and 0.18% greater than B1, respectively.

These mixed powders were pressed with a lubricant for pressing, pressed at a pressure of 1 ton / cm 2 and vacuum-sintered. Even though the mixed powder used was the same, the sample names were classified according to sintering conditions and heat treatment conditions. The sintering conditions and characteristic values of the sample are shown in (Table 2).
Here, the “slow cooling” of the sintering conditions is a process of cooling at 1380 ° C. for 1 hour by vacuum sintering and then cooling (slow cooling) from 1350 ° C. to 800 ° C. at 10 ° C./min. .
In addition, “quick cooling” in the sintering conditions is a process of cooling at 1380 ° C. for 1 hour by vacuum sintering and then cooling (rapid cooling) by introducing an inert gas from 1350 ° C. to 800 ° C. at 30 ° C./min. “Strong cooling” refers to a process of introducing an inert gas from 1350 ° C. to 800 ° C. and cooling (rapid cooling) at 50 ° C./min.
“Reheating and quenching” under sintering conditions means that the sintered material is reheated at 1340 ° C. for 15 minutes in a vacuum furnace, and an inert gas is introduced from 1340 ° C. to 800 ° C. during cooling at 30 ° C./min. The process was cooled (rapidly cooled) at "Reheating and rapid cooling". The re-sintered product was reheated at 1340 ° C for 15 minutes in a vacuum furnace and the temperature from 1340 ° C to 800 ° C was reduced to 50 ° C during cooling. It is a process of cooling (rapid cooling) at a rate of ° C / min.
Here, the measurement method of the maximum nest diameter (μm) in (Table 2) is in accordance with the above-mentioned <Definition of the size of the nest caused by free carbon and its measurement method>.

A11, A21, B11, B21, B41, and B51 have sintering conditions of “slow cooling”. The ones with zero carbon addition (A11, B11) in Table 1 have no free carbon even after sintering, and the evaluation of the nest is A02 in FIG. 1 of CIS006C and is A02 or less. The carbon added (A21, B21, B41, B51) still had free carbon after sintering, and the nest was also determined as C02-C06 in the C form of FIG. 4 of CIS006C.
Further, for A21 and B21, which will be described more specifically, when the surface was polished to a mirror surface and examined at a magnification of 100, both were judged to be about C04 by CIS006C. In other words, a large free carbon nest was observed in a mixture of 80-100 μm and a small nest of about 25 μm.
In A22 and B22, A21 and B21 (sintered products) were reheated in the same vacuum furnace, held and cooled at 1340 ° C. for 15 minutes, and cooled from 1340 ° C. to 800 ° C. at a cooling rate of 30 ° C./min (rapid cooling). )did. The condition of the nests of these cemented carbides was polished by a method according to CIS006C as in the case of other samples, and examined at 100 times.
The maximum diameter of the A22 nest was 15 μm or less, and the maximum diameter of the B22 nest was 20 μm or less. The bending strength and hardness were also measured. A23 and B24 are obtained by vacuum-sintering the mixed powder under the same conditions as described above and then cooling (quenching) at 30 ° C./min. The mixed powder of B4 and B5 is also cooled after vacuum sintering. Table 2 shows the sintering conditions and results.

A11, B11 in which the sintering condition is “slow cooling” and the additional carbon amount is 0%, and A21 and B21 in which the sintering condition is “slow cooling” and the additional carbon amount is 0.14%. Since free carbon precipitates in B21, the bending strength and hardness are reduced. However, even if free carbon appears like A22, A23, B22, B24, it is possible to finely disperse the free carbon by “quickly cooling” or “reheating and quenching” the sintering conditions. When becomes smaller, the bending strength becomes equivalent to A11 and B11 where no free carbon appears. Although the hardness tends to be slightly lower than A11 and B11 where no free carbon appears, there is almost no difference.
B52 had slightly more nests and one nest with a maximum diameter of 20-25 μm in 2 out of 10 fields. B23 was obtained by reheating B21 to 1340 ° C. and rapidly cooling to 800 ° C. at 50 ° C./min. The nest improved from B22, and the size of the nest was small and all were 10 μm or less. All of B42 also had a nest size of 10 μm or less.
Thus, normally, when the cemented carbide contains free carbon that causes nests, the resulting cemented carbide is free carbon when cooled by general sintering conditions and cooling methods (slow cooling). Compared to cemented carbides that do not contain steel, the bending strength and hardness will be small, but quenching or rapid cooling after sintering, or slow cooling after sintering, followed by reheating quenching or reheating rapid quenching As a result, even if the cemented carbide contains free carbon, the free carbon nests of the cemented carbide are dispersed, resulting in the same level of bending strength and hardness as the cemented carbide not containing free carbon. It becomes possible to produce a cemented carbide alloy having the same.

(Example 2)
Examples of cutting tool materials are described below.
The mixed powder before sintering was prepared by blending with a composition of (Table 3) using a commercially available raw material, and wet ball milling and drying by a general method using alcohol. All of these mixed powders were pressed at a pressure of 1 ton / cm 2 with a lubricant for pressing. C11 and C21 were cooled at 1400 ° C. for 1 hour in vacuum sintering and then cooled (cooled slowly) from 1380 ° C. to 800 ° C. at 10 ° C./min (corresponding to “slow cooling” in the sintering conditions).
On the other hand, C23 was cooled at 1400 ° C. for 1 hour in vacuum sintering and then cooled, and an inert gas was introduced from 1380 ° C. to 800 ° C. and cooled (rapidly cooled) at 50 ° C./minute (sintering conditions “strong” Equivalent to “quick cooling”).
And C22 reheated and quenched C21. “Reheating and rapid cooling” as a sintering condition is a process of holding at 1380 ° C. for 30 minutes in a vacuum furnace and cooling at 30 ° C./min. C22 did not have a nest of 20 μm or more. The size of the C23 nest was 10 μm or less. The results are shown in (Table 4).

Further, C11, C21, C22, and C23 were used as a base material, and TiC was coated by 7 μm CVD. In C11, an η phase of 1-3 μm was formed at the boundary between the TiC film and the base material, but not in C21. Data for verifying Non-Patent Document 3 was obtained. C22 and C23 did not generate an η phase at the boundary between the TiC film and the base material, and had the same result as C21. That is, even if free carbon is finely dispersed in the base material, the effect of reducing the η phase is the same.

(Example 3)
Examples of cemented carbide having a de-β layer on the surface frequently used as a base material for CVD will be described below.

The mixed powder before sintering was prepared by blending with a composition shown in Table 5 using a commercially available raw material, mixing with a wet ball mill by a general method using alcohol, and drying. These mixed powders were pressed at a pressure of 1 ton / cm 2 with the addition of a lubricant for pressing. E1 and F1 were cooled after being held at 1400 ° C. for 1 hour by vacuum sintering and then cooled (slowly cooled) from 1380 ° C. to 800 ° C. at 10 ° C./min (corresponding to “slow cooling” in the sintering conditions).
On the other hand, F2 was cooled at 1400 ° C. for 1 hour by vacuum sintering and then cooled, and an inert gas was introduced from 1380 ° C. to 800 ° C. and cooled (rapidly cooled) at 30 ° C./min (“swift cooling” in the sintering conditions) Equivalent). The results are shown in (Table 6). In each of E1, F1, and F2, a 10-20 μm de-β layer was formed on the surface. Even if free carbon is finely dispersed, a de-β layer can be formed. These samples had a β-free layer on the sintered surface, and the bending strength was not measured.

Example 4
Experiments were conducted on the dimensional accuracy of the cutting edge-exchangeable cutting tip.
Using a mixed powder of C1 and C2 in Table 2 of Example 2 and adding a lubricant for pressing, a plurality of blade tip replaceable cutting tips, model number SNMA432, are pressed at a pressing pressure of 1 ton / cm 2 and sintered. The dimensional accuracy was measured. The result of (Table 7) was obtained. As for the sintering conditions, G11 is the same as C11, G21 is the same as C21, G22 is the same as C22, and G23 is the same as C23.
The “in-chip dimensional difference” in Table 7 is the difference between the maximum value and the minimum value when four sides of one SNMA 432 (square) are measured with a micrometer.
“10 maximum and minimum differences” in (Table 7) is obtained by measuring four sides of 10 SNMA 432 and subtracting the minimum value from the maximum value.

G22 and G23 in which free carbon is finely dispersed have less dimensional variation than G11 that does not contain free carbon.
G11, G22, and G23 were coated with TiC 2 μm + TiN 3 μm by ion plating, which is a kind of PVD, and the same measurement was performed. The in-chip dimensional differences of the PVD-coated G22 and G23 and the PVD-coated G11 were almost the same as before coating, and the coated G22 and G23 were smaller in dimensional variation than the coated G11.
Furthermore, G11, G22, and G23 were coated with 7 μm of TiC by the CVD method, and the same dimensional measurements were made for comparison. The dimensional variation was almost the same as before coating, and the coated G22 and G23 had smaller dimensional variation than G11.

(Example 5)
Cylindrical cemented carbide sintered bodies were fabricated and dimensional accuracy was compared.
The mixed powder of B1, B2, and B4 of Example 1 was used by adding a lubricant for pressing, and the pressing was performed at 1 ton / cm2, and a plurality of sintered bodies having an outer shape 50D, an inner diameter 20d, and a height 50 (unit mm) were used. The dimensional accuracy was compared. The results are shown in (Table 8).

The sintering conditions followed the sintering conditions for the B1, B2, and B4 powders. In the dimension measurement, the outer shape of the sintered body was measured, and the difference between the maximum diameter and the minimum diameter was determined as the quality accuracy determination. The difference between the maximum and minimum outer diameters of one sintered body and the difference between the three maximum and minimum diameters are displayed. It can be seen that H24 and H42 in which free carbon is finely dispersed have better dimensional accuracy than H11 which does not contain free carbon.

(Example 6)
The processing efficiencies when producing cemented carbide products were compared.
Peripheral turning was performed using H11 and H24 of Example 5 as work materials. The cutting tool used was a polycrystalline diamond sintered body, model number TNGA432. Cutting conditions were cutting speed (v) = 15 m / min, feeding speed (f) = 0.1 mm / rev, and cutting depth (d) = 0.1 mm.
The time for removing the outer peripheral sintered skin is natural, but H11 with a lot of damage and a large allowance required 1.5 times as long as H24 with less damage.
Further, in order to compare the machinability of H11 and H24, after removing the sintered skin, the tool was replaced with a new one, and cutting was performed for 20 minutes under the same conditions, and the progress of wear of both tools was compared.
Tool wear (flank wear) due to cutting of H11 was 0.11 mm, and that of H24 was 0.08 mm. This indicates that H24 has better machinability than H11. That is, the cemented carbide of the present invention has not only improved dimensional accuracy of the sintered product but also excellent machinability. Therefore, it was confirmed that it was possible to provide cemented carbide processed products with low processing costs.

(Example 7)
The relationship between the fcc lattice constant of the binder phase (Cо phase) and the cutting performance was investigated.
Using the C1 powder of Example 2, SNMA432 was pressed at 1 ton / cm 2, vacuum sintering was held at 1400 ° C. for 1 hour, and then rapidly cooled (strong and rapid cooling) at a cooling temperature of 70 ° C./min. The sample number was G24. (Example 4) The mixed powder is the same as (Example 2), and G11, G21, G22, G23 of (Example 4) and G24 described above were used as samples, and the lattice constant and cutting performance were compared. . For measurement of the lattice constant, X-ray diffraction using Cu as a target was used.

Cutting conditions (turning) are: Work material: SCM3, Cutting speed v = 120 m / min, Feed f = 0.4 mm / rev, Depth of cut d = 2 mm, Cutting time t = 30 minutes. Wear was measured.
Further, G11 and G21 to G24 were coated with TiC 2 μm + TiN 3 μm by PVD, and a cutting test was performed. The cutting conditions (turning) of the coated cemented carbide using G11, G21 to G24 are: Work material: SK5, v = 100 m / min, f = 0.5 mm / rev, d = 2 mm, t = 3 min, after the test The amount of plastic deformation of the blades (sagging of the rake face) was compared. The results are shown in (Table 9).
G21 containing free carbon in a conventional manner was inferior in performance to G11. However, it is obvious that both the cemented carbide and the coated cemented carbide having a high lattice constant and finely dispersed free carbon are superior to G21, but are superior to G11 not containing free carbon.

Claims

A cemented carbide consisting of tungsten carbide (WC) and cobalt (Cо) containing carbon in a range that does not contain solid carbon in the liquid phase at a high temperature, finely dispersed free carbon,
The cemented carbide having a maximum nest diameter caused by the free carbon of 20 μm or less is referred to as cemented carbide A,
A cemented carbide having a maximum nest diameter due to the free carbon of 15 μm or less is defined as cemented carbide B;
A cemented carbide having a maximum nest diameter caused by the free carbon of 10 μm or less is cemented carbide C,
In the cemented carbide A, B or C, a cemented carbide containing 0.02% or more and 0.15% or less of the amount of free carbon is defined as cemented carbide D,
In the cemented carbide A, B, C or D, a cemented carbide to which chromium carbide or chromium nitride of 2 to 18% of the amount of cobalt (Cо) is added is defined as cemented carbide E.
In the cemented carbide A, B, C, D or E, a cemented carbide whose cemented phase (Co phase) fcc lattice constant of the cemented carbide is 3.560Å or more is referred to as cemented carbide F.
In the cemented carbide A, B, C, D, E or F, a part of tungsten carbide (WC) is a carbide of a transition metal of group 4 or 5 element of the periodic table (however, excluding W), nitride, Carbide nitride, carbide of W and transition metal carbide, nitride, double carbide of carbonitride, carbide carbide replaced with any one of these or a combination thereof is cemented carbide G,
In the cemented carbide G, a cemented carbide having a de-β layer formed on the surface of the cemented carbide and having a thickness of 1 to 30 μm is referred to as a cemented carbide H.
When producing any one of the cemented carbides A, B, C, D, E, F, G, and H, the mixed powder for producing the cemented carbide is produced at a sintering temperature equal to or higher than the liquid phase appearance temperature. A method for producing a cemented carbide comprising: a step of quenching from a temperature higher than a liquid phase appearance temperature after sintering, or a step of reheating to a temperature higher than the liquid phase appearance and quenching.
The method for producing a cemented carbide according to claim 1, wherein a cooling rate from a liquid phase appearance temperature to 800 ° C is set to 30 ° C / min or more in the rapid cooling step and the reheating and rapid cooling step.
A method for producing a coated cemented carbide comprising using the cemented carbide produced by the method for producing a cemented carbide according to claim 2 as a base material when producing the coated cemented carbide.
4. A cutting edge-exchangeable cutting tip characterized by using the cemented carbide manufacturing method according to claim 2 or 3 when manufacturing a cutting edge-exchangeable cutting tip.
A cemented carbide processed product using the cemented carbide manufacturing method according to claim 2 or 3 as a cemented carbide to be used in manufacturing a cemented carbide processed product.
Made of cemented carbide consisting of tungsten carbide (WC) and cobalt (Cо) containing carbon in a range that does not contain solid carbon in the liquid phase at high temperatures, and finely dispersed free carbon. A cutting edge exchangeable cutting tip,
The cemented carbide having a maximum nest diameter caused by the free carbon of 20 μm or less is referred to as cemented carbide A,
A cemented carbide having a maximum nest diameter due to the free carbon of 15 μm or less is defined as cemented carbide B;
A cemented carbide having a maximum nest diameter caused by the free carbon of 10 μm or less is cemented carbide C,
In the cemented carbide A, B or C, a cemented carbide containing 0.02% or more and 0.15% or less of the amount of free carbon is defined as cemented carbide D,
In the cemented carbide A, B, C or D, a cemented carbide to which chromium carbide or chromium nitride of 2 to 18% of the amount of cobalt (Cо) is added is defined as cemented carbide E.
In the cemented carbide A, B, C, D or E, a cemented carbide whose cemented phase (Co phase) fcc lattice constant of the cemented carbide is 3.560Å or more is referred to as cemented carbide F.
In the cemented carbide A, B, C, D, E or F, a part of tungsten carbide (WC) is a carbide of a transition metal of group 4 or 5 element of the periodic table (however, excluding W), nitride, Carbide nitride, carbide of W and transition metal carbide, nitride, double carbide of carbonitride, carbide carbide replaced with any one of these or a combination thereof is cemented carbide G,
In the cemented carbide G, a cemented carbide having a de-β layer formed on the surface of the cemented carbide and having a thickness of 1 to 30 μm is referred to as a cemented carbide H.
Cutting edge exchange type characterized in that it is made of any one of the above cemented carbides A, B, C, D, E, F, G, H or a coated cemented carbide using these as a base material. Cutting tip.
Made of cemented carbide consisting of tungsten carbide (WC) and cobalt (Cо) containing carbon in a range that does not contain solid carbon in the liquid phase at high temperatures, and finely dispersed free carbon. It is a cemented carbide processed product,
The cemented carbide having a maximum nest diameter caused by the free carbon of 20 μm or less is referred to as cemented carbide A,
A cemented carbide having a maximum nest diameter due to the free carbon of 15 μm or less is defined as cemented carbide B;
A cemented carbide having a maximum nest diameter caused by the free carbon of 10 μm or less is cemented carbide C,
In the cemented carbide A, B or C, a cemented carbide containing 0.02% or more and 0.15% or less of the amount of free carbon is defined as cemented carbide D,
In the cemented carbide A, B, C or D, a cemented carbide to which chromium carbide or chromium nitride of 2 to 18% of the amount of cobalt (Cо) is added is defined as cemented carbide E.
In the cemented carbide A, B, C, D or E, a cemented carbide whose cemented phase (Co phase) fcc lattice constant of the cemented carbide is 3.560Å or more is referred to as cemented carbide F.
In the cemented carbide A, B, C, D, E or F, a part of tungsten carbide (WC) is a carbide of a transition metal of group 4 or 5 element of the periodic table (however, excluding W), nitride, Carbide nitride, carbide of W and transition metal carbide, nitride, double carbide of carbonitride, carbide carbide replaced with any one of these or a combination thereof is cemented carbide G,
The cemented carbide processed product is obtained by subjecting one of the cemented carbides A, B, C, D, E, F, and G to electrical discharge machining, grinding / polishing, cutting, or a combination thereof. A cemented carbide product that is formed by processing.