JP2760926B2 - High-strength cemented carbide composite material combining low carbon steel and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength cemented carbide or cemented carbide-steel alloy useful as a wear-resistant tool or a large-sized tool, and a method for producing the same.

[0002]

2. Description of the Related Art Cemented carbides represented by the WC-Co system are:
Due to its excellent wear resistance, heat and corrosion resistance, and higher toughness than ceramics, it has been applied to many industrial fields such as cutting tools, rolls, nozzles, and civil engineering tools. However, cemented carbides are difficult-to-process and hard-to-weld materials, like ceramics, and are expensive, so their application fields are often limited. As one of the remedies, compounding by brazing with another material such as steel, which is inexpensive and excellent in workability, has been implemented. Also in this brazing, a high stress is generated due to a difference in the coefficient of thermal expansion between the base material, the brazing material and the cemented carbide, so that a crack may be generated in the brazing material or the cemented carbide. In addition, when the wettability of the brazing material is poor, the joining is poor, and even if the joining is complete, only a strength of about 10 to ²⁰ kg / mm ² can be expected by the shearing force.

[0003] Japanese Patent Publication No. 57-57525 discloses that the outer periphery of an already sintered cemented carbide is substantially the same in composition as the cemented carbide and larger than the outer shape of the cemented carbide, and has an approximate inner shape. An annular cemented carbide raw material powder compact or this pre-sintered body is coaxially arranged with a gap between the cemented carbide,
There is disclosed a technique in which a cemented carbide raw material powder compact or this pre-sintered body is sintered and integrated with the inner cemented carbide by shrinkage during sintering. However, this technique is a technique applicable to a cylinder such as a cemented carbide roll, such as a cemented carbide roll, and cannot be applied to products having a general shape. This technique does not provide a composite of cemented carbide and steel.

[0004] Japanese Patent Publication No. 2-28428 discloses that in joining one or more cemented carbides, a thin sheet of Fe-based metal is inserted into the contact surfaces of the cemented carbides, and one of the contact surfaces is contacted. A technique is described in which a high energy beam is applied to a part or the entire surface to melt and solidify an Fe-based thin plate or cemented carbide in a slit shape to join cemented carbides together. The high-energy beam used here is an electron beam or a laser beam. However, since the energy density is increased by narrowing the beam diameter, it takes a long time to join over a wide area. In view of the fact that the irradiation is performed from a distance, application to relatively small products has been limited. This technique is also effective for joining cemented carbide and steel, but has the same disadvantages as described above.

Japanese Patent Application Laid-Open No. 63-125602 discloses that a used part including a part to be processed and a non-used part other than the used part are divided into a used part and a non-used part. There is described a technique in which a used part and a non-used part are diffused and bonded to each other by using materials having different thermal expansion coefficients to give a residual stress to the used part. Here, when the unused portion is made of a material having a relatively high coefficient of thermal expansion, it is disclosed that, for example, the amount of the binder phase should be increased, or a component having a large coefficient of thermal expansion such as TiC should be increased. ing.
Such a technique requires a structure in which the contact area between the unused portion and the used portion is large, and the difference in thermal expansion coefficient between the unused portions directly affects the used portion. Thus, certain restrictions must be imposed on the field of application. Japanese Patent Publication No. 43579/1990 discloses a method for manufacturing a joining member made of cemented carbide and sintered steel. In this method, sintering of the sintered steel and brazing are performed simultaneously in a reducing atmosphere using a specific brazing material.

[0006]

As described above, the conventional techniques have the respective features, but in the case of the brazing method, for example, the residual strain due to the difference in the coefficient of thermal expansion is large, and Since the heat resistant temperature of the material is low, the strength of the entire joined body is low. Therefore, it is desired to develop a brazing material having high joining strength and capable of relieving stress.However, if there is a cemented carbide having excellent toughness and high toughness and ductility that does not cause cracking at the time of joining, It is expected that the compounding with steel can be performed very easily by using this. Furthermore, if the cemented carbide can be joined with ordinary ingots, the range of industrial use of cemented carbide will be greatly expanded,
Cost reduction and long life can be achieved.

[0007] It is conceivable to directly join a high-hardness cemented carbide with steel, but there is a problem that the steel melts at the sintering temperature of the high-hardness cemented carbide. It is also conceivable to directly join at a low temperature by solid-phase diffusion bonding or the like in order to join a hardened cemented carbide with high hardness in advance and steel.
It is necessary to strictly control the smoothness and cleanliness of the joint surface, and it is necessary to maintain the pressurized state for a long time. Further, a low-strength layer is formed at the interface of the joined body due to the reaction between the steel and the cemented carbide, and the strength of the entire joined body is reduced due to stress based on the difference in thermal expansion between the two, and in some cases, cracks occur. In such a situation, it was extremely difficult to directly join steel and a high-hardness cemented carbide.

[0008]

Means for Solving the Problems The present inventors have made various studies to solve the above-mentioned problems of the prior art. Then, a high-strength cemented carbide composite material as described below was obtained. In this invention, the cemented carbide of high hardness, the cemented carbide for joining and the cemented carbide and steel are each diffusion-bonded, and the ratio of the bonding phase in the cemented carbide for joining is determined by the high hardness. From the binder phase in cemented carbide
One feature is that it is larger by 45% by weight. Still another feature is that the combined volume of the cemented carbide and the high-hardness cemented carbide is smaller than the volume of the steel and the thickness of the η phase between the cemented carbide and the steel is controlled. There is a feature in the point. The cemented carbide comprises a hard phase and a binder phase, and the hard phase is composed of known compounds such as carbides, nitrides, carbonitrides of WC and transition metals of groups 4a, 5a and 6a of the periodic table. As a component of the binder phase, the main component is an iron group metal, but a known substance such as Cr can also be added. The cemented carbide for joining used in the present invention desirably has intermediate properties between the properties of steel and the cemented carbide of high hardness for the purpose of the invention, and the amount of the binder phase in the sintered body is 35 to 50%. It is preferable to use a cemented carbide in the range of 50% by weight.

Here, Co is usually used as the binder phase, but various compositions may be used depending on the conditions of use. When used under conditions requiring corrosion resistance, C
An o-Ni binder phase is required. If mechanical strength, corrosion resistance and oxidation resistance are required, a Co-Ni-Cr based binder phase is required, and if corrosion resistance and oxidation resistance are required. Is Ni-
A Cr-based binder phase is used. For example, in the case of tools for civil engineering, when drilling holes in rock, the strength is high.
An o-based or Co-Ni-Cr-based material is used. When a hole is made in a clay ground, the binder phase is determined by the properties of the clay. When various lubricants are used at a high temperature such as a roll, a Co-Ni-Cr-based binder phase is used.

According to the present invention, since the amount of the binder phase in the cemented carbide is closely related to the sintering temperature, the amount of the binder phase in the cemented carbide for joining is set to an unusually large amount. This has been achieved by the addition. That is, the cemented carbide generally used has the same amount as the 5 to 20% by weight binder phase used in the high-hardness cemented carbide of the present invention. The amount is a desirable amount for a high-hardness cemented carbide. If the amount of the binder phase in the cemented cemented carbide is less than 35 % by weight, it is necessary to control the sintering temperature extremely precisely in order to approach the sintering temperature of the hardened cemented carbide. On the other hand, if the amount of the binder phase exceeds 50% by weight, the binder phase becomes a liquid phase at the time of sintering or joining with a high-hardness cemented carbide.

The configuration as described in the present application is characterized in that steel, a high-hardness cemented carbide and a cemented carbide for joining can be diffusion-bonded in one step. The steel used at this time desirably contains 0.4% by weight or less of carbon. If it is less than 0.4%, at the time of joining the cemented cemented carbide and steel, the carbon in the cemented cemented carbide moves toward the steel, and there is a shortage of carbon in the cemented cemented carbide. Occurs, and a compound of high hardness WxCoyCz (a so-called η phase) is formed therein. For example, W3C
Compounds such as o3C exist. The features of the present invention are:
The greatest feature is that the η phase generated at the interface between the steel having a low carbon content and the cemented carbide for joining as shown in FIGS. 1 and 2 is controlled to prevent the strength of the joining interface from decreasing. The hardness of the η phase is higher than that of the cemented carbide as shown in FIG. Generally, the η phase is considered to be brittle, but its thickness is 50 μm.
If it exceeds, the strength of the entire composite material decreases. 1.5 μm or less
When it is full, it is difficult to confirm the generation of the η phase, but in the present invention, the carbon content of the steel and the sintering temperature of the cemented carbide for joining are
Can control the thickness of the η phase to 1.5 μm to 50 μm.

[0012] Such a high-strength cemented carbide composite material is manufactured as follows. That is, a high-strength cemented carbide mainly composed of 5 to 20% by weight of a binder phase and WC is sintered at a temperature of 1360 to 1550 ° C. in advance, and 35 to 50% by weight of a binder is brought into contact therewith. A cemented carbide powder for joining consisting of a phase and WC or a pre-pressed or pressed body or sintered body is arranged, and steel is further arranged to 1200-200.
It can be obtained by sintering at 1360 ° C. at the same time as diffusion bonding or diffusion bonding. Temperature below 1200 ° C
In this case, the bonding strength decreases, and if it exceeds 1360 ° C, the hardness of steel
Decrease. At this time, if steel that can be quenched by air cooling is used, diffusion bonding, sintering, and quenching can be performed simultaneously, and the thickness of the η phase can be further reduced. In the above-described diffusion bonding and sintering, the hot press method enables sintering with a high density even at a low sintering temperature, and also keeps the bonding strength high. On the other hand, from the viewpoint of economy such as mass production, normal pressure sintering without applying pressure is more desirable. In this case, it is more preferable that the hardened cemented carbide is used as the lowermost layer, and the cemented cemented carbide is further stacked thereon in this order. In this case, if necessary, it is possible to further load a heavy object thereon and apply a desired load. In this way, a pressure of 5 to 100 kg / cm ² can be applied to the above-mentioned bonding interface.

[0013]

According to the present invention, a cemented carbide powder for joining that can be sintered at a relatively low temperature is laminated on a pre-sintered high-hardness cemented carbide,
By heating to the former optimum sintering temperature, the sintering and the joining with a high-hardness cemented carbide as a counterpart material are simultaneously performed. Furthermore, since the cemented carbide for joining can be sintered even at a temperature at which the steel does not melt, a cemented carbide powder layer is interposed between the cemented carbide of high hardness and steel, and By heating to the sintering temperature, a composition gradient body having a sequentially reduced hardness can be produced.

According to these methods, a high-hardness cemented carbide and a low-hardness cemented carbide are sintered at the optimum sintering temperature, respectively, so that a good structure free from defects such as pores is obtained. Further, in bonding with steel, an η phase deficient in carbon is formed at the interface between the cemented carbide and steel, but the thickness is small, so that there is almost no decrease in the strength of the bonding interface. For this, 0.4w
This can be achieved by using a steel containing t% or less of carbon and a cemented carbide having a low sintering temperature. These composites act to relieve stress because the cemented carbide for joining has high toughness and high ductility, and the cemented carbide for joining has a larger coefficient of thermal expansion than that of high-hardness cemented carbide. Since the thermal expansion coefficient is close to the expansion coefficient, the thermal stress at the time of joining becomes small, and the joining property with steel becomes extremely good.
In particular, it has been clarified that the range of application is remarkably wide because fusion welding is extremely easy with a combination of low carbon steels.

In order to achieve the object of the present invention, it is preferable that the cemented cemented carbide functioning as a stress relaxation layer has a larger volume than a high-hardness cemented carbide. Such a composite material requires higher strength bonding when bonding with steel or the like.For example, when bonding steel and a cemented carbide for joining, a liquid phase is contained in the cemented carbide for joining. In many cases, bonding is performed at a temperature close to the temperature at which it appears. Therefore, stable joining is performed when the surface where the cemented cemented carbide and the cemented cemented carbide are in contact with each other is farther from the joint surface between the cemented cemented carbide and steel. Therefore, it is desirable that the cemented carbide for joining has a larger volume than the hardened cemented carbide. The reason why the combined size of the cemented cemented carbide and the high-hardness cemented carbide is preferably smaller than the size of the steel is mainly due to the price. However, in consideration of the thermal efficiency, if the treatment is performed by extreme heating such as welding, this does not cause a serious problem. However, as in the present application, it is made of a high-hardness cemented carbide, a cemented cemented carbide and steel. In the case where the entire combination is heated, the size of the inside of the furnace chamber is limited. Therefore, it is not economical to heat a large combination unnecessarily. Therefore, the optimum size of the steel is determined mainly by economic efficiency.

If the ratio of the binder phase in the cemented cemented carbide is greater than 10 to 45% by weight of the binder phase in the high-hardness cemented carbide, if the difference is less than 10% by weight, the sintering of the two is hardened. This is because the sintering temperature is too close to control the temperature industrially. If it exceeds 45% by weight, at least the proportion of the binder phase in the cemented carbide for joining exceeds 50% by weight, so that it becomes very difficult to maintain the shape during sintering of the cemented carbide for joining. That's why. Further, it is desirable that at least one of the joining surfaces is mainly flat. The reason for this is that the plane is a simple shape and an industrially desirable shape. As a matter of course, a part of the plane may include a curved surface or the like.

[0017]

【Example】

(Example 1) WC powder having an average WC particle size of 5.0 µm and Co powder were mixed so as to be 85% WC-15% Co by weight, and then an embossed body having a diameter of 20 mm and a thickness of 10 mm was produced. The embossed body was sintered in a vacuum sintering furnace at 1400 ° C. for 1 hour to obtain a high-hardness cemented carbide. On the other hand, average particle size5.
A mixed powder of 0 μC WC powder and Co powder of WC 55% -Co 45% by weight was prepared and used as cemented cemented carbide powder. Insert the high-hardness cemented carbide into a cemented carbide mold slightly larger in diameter than the high-hardness cemented carbide described above, and laminate the cemented carbide powder for bonding to a thickness of 15 mm thereon. And
Pressure was applied by applying a pressure of about 1 ton / cm ² .

A combined body in which a cemented carbide for bonding is stamped on a cemented carbide of high hardness is taken out of a cemented carbide mold,
Further, S45C steel having a thickness of 30 mm is further laminated thereon, and under a vacuum atmosphere, 1250 ° C., 1 hour, pressure 50 kg / c.
Hot press sintering at m ² . After polishing and lapping the cross section of the joined body and observing with a microscope, the joining interface between the cemented cemented carbide and the high-hardness cemented carbide has the composition of a normal cemented carbide. About 30 at the alloy interface
Although an η phase having a thickness of μm was formed, there were no defects such as pores. Combinations of similar size were sintered at 1250 ° C. and 1290 ° C. without pressure. 1250 ° C
Some pores were found in the cemented cemented carbide for those sintered at 1290, but no pores were found for the one sintered at 1290 ° C. In any case, the interface between the cemented carbide and steel is η
A phase had formed.

Example 2 W having an average particle size of WC of 4 μm
After the C powder and the Co powder were mixed so that WC was 90% -Co 10% by weight, an embossed body having a diameter of 100 mm and a thickness of 20 mm was produced, and a high-hardness cemented carbide was obtained. Next, the embossed body was sintered at 1440 ° C. in a vacuum sintering furnace. On the other hand, WC powder and Co powder having an average particle size of 4 μm
A mixed powder of 5% by weight was prepared and used as a cemented carbide powder for joining. A high-hardness cemented carbide is inserted into a cemented carbide mold having a slightly larger diameter than the high-hardness cemented carbide, and a cemented carbide for bonding is laminated thereon to a thickness of 30 mm. ,
Further, a steel plate of S25C, which is an ingot having a diameter of 100 mm and a thickness of 50 mm, was laminated thereon, and pressure-sintered at 1270 ° C. under a pressure of about 10 kg / cm ² . The combined body was taken out of the cemented carbide mold and sintered for 1 hour under a vacuum atmosphere. When the strength of the obtained sintered body was measured, it was almost the same as that of the cemented carbide for joining. Combinations of similar size were sintered at 1270 ° C. and 1300 ° C. without pressure. Those sintered at 1270 ° C. had pores in the cemented carbide, but those sintered at 1300 ° C. did not have pores. An η phase was formed at the interface between the steel and the cemented carbide for joining.

[0020]

At present, there are many examples in which only high-hardness cemented carbide is applied to tools or mechanical parts. However, compared to steel and the like, cemented carbides have poor ductility and toughness, and thus have not been used in fields with large impact loads. The composite cemented carbide according to the present invention can be a composite cemented carbide with significantly improved ductility because the cemented carbide having a high Co content becomes a relaxation layer against impact load during use. . In addition, for joining the hardened cemented carbide and steel, Cu
Alternatively, brazing using a soft brazing material such as Ag is often used, but the cemented carbide composite according to the present invention has a low joining surface of low carbon steel, so that the range of choice of brazing material in brazing is widened, The joining density can be improved. Furthermore, since it is a composite including steel, a fusion welding method, which was almost impossible with conventional cemented carbide, can be applied, and the range of use of cemented carbide can be greatly expanded.

[Brief description of the drawings]

FIG. 1 shows a hardness distribution of a composite material obtained by the present invention.

FIG. 2 shows a structure photograph of the composite material obtained by the present invention.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masahiro Sakai 1-1-1 Matsuba-cho, Hiroshima-cho, Sapporo-gun, Hokkaido 8 (72) Inventor Yasugi Miyakoshi 505-27 Teinemaeda, Teine-ku, Sapporo-city, Hokkaido 27 (72) Inventor Isao Makino (2) Inventor Tatsuya Kanayama 776, Naie-cho, Naie-cho, Sorachi-gun, Hokkaido Inside the Hokkaido Sumiden Precision Co., Ltd. (72) Inventor Kazuhiro Yamaguchi, Naie-cho, Hokkaido Sorachi-gun, Sapporo City, Hokkaido 776 Naie, Hokkaido Inside Sumitomo Precision Co., Ltd. (72) Inventor Masao Maruyama, 776 Naie, Naie-cho, Sorachi-gun, Hokkaido In-house Hokkaido Sumiden Precision Co., Ltd. (72) Isao Shibata, 776 Naie, Naie-cho, Sorachi-gun, Hokkaido Hokkaido Sumitomo Precision Co., Ltd. (72) Inventor Yoshihiro Minato 1-1-1, Kunyokita, Itami-shi, Hyogo Prefecture Sumitomo Electric The Corporation Itami Works (56) Reference Patent Sho 52-50906 (JP, A) JP Akira 53-1609 (JP, A)

Claims (4)

(57) [Claims] 1. A cemented carbide having a high hardness and a cemented carbide for joining, and a cemented cemented carbide and a steel are diffusion-joined, and a binder phase in the cemented carbide for joining is an iron group metal; And the proportion of the binder phase in the sintered body is 35 to 50% by weight, and the thickness of the η phase between the cemented cemented carbide and the steel is 50 μm or less and 1.5 μm or less.
As described above, the cemented carbide for joining has a larger volume than the cemented carbide of high hardness, and at least one of the diffusion joining surfaces is a flat surface. Hard alloy composite material. 2. The high-strength cemented carbide composite material according to claim 1, wherein the carbon content in the steel is 0.4% by weight or less. 3. A cemented carbide of high hardness comprising 5 to 20% by weight of a binder phase and a hard phase is sintered at a temperature of 1360 to 1550.degree. A cemented carbide powder for bonding consisting of a binder phase and a hard phase by weight%, or a pressed body or sintered body that has been pressed in advance is arranged.
Further, the steel is disposed in contact with the cemented cemented carbide and sintered and / or diffusion-bonded, and η between the cemented cemented carbide and the steel is determined.
A high-strength cemented carbide composite combining low carbon steel, characterized in that the thickness of the cemented cemented carbide after sintering has a phase thickness of 50μ or less and 1.5μ or more and is larger than the volume of the high-hardness cemented carbide. material. 4. Diffusion bonding and / or sintering under a pressure of 5 to 150 kg / cm ^2.
A method for producing a high-strength cemented carbide composite material comprising a combination of the low-carbon steel according to the above item.