JP4170544B2 - Boron nitride dispersed silicon carbide-carbon composite - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a boron nitride-dispersed silicon carbide-carbon composite material used in a high-temperature oxidizing atmosphere.
[0002]
[Prior art]
Carbon materials are used for various heat treatment jigs such as metal melting crucibles, ceramic sintering crucibles, metal deposition jigs, continuous casting dies, casting molds, etc. due to their superior properties at high temperatures. Widely used as a heat-resistant material.
[0003]
However, the carbon material has a drawback that it is easily oxidized and consumed in a high-temperature oxidizing atmosphere, and also reacts with the object to be processed when used in the various applications even under a reducing atmosphere, Has dissolved and penetrated into the carbon material, and the carbon material is damaged. Various attempts have been made to prevent the carbon material from being oxidized and the dissolved material from penetrating.
[0004]
In order to make up for the drawbacks of the carbon material, the present inventors provide silicon (hereinafter referred to as “Si”) powder and boron carbide (hereinafter referred to as “B ₄ C”) on the surface of the substrate made of the carbon material. Applying a slurry consisting of powder and thermoplastic resin and heat-treating it to form a deep silicon carbide-carbon (hereinafter referred to as “SiC-C”) composite layer on the surface of the base material. An excellent carbon product was developed and applied (Japanese Patent Laid-Open No. 10-212182).
[0005]
[Problems to be solved by the invention]
However, when a SiC-C composite layer is formed on a surface that contacts a workpiece such as metal or ceramics, such as a crucible for melting metal, a crucible for sintering ceramics, a die for continuous casting, a casting mold, etc. There has been a problem that the object is fixed to the surface of a heat treatment jig such as a tray, crucible or mold after cooling.
[0006]
Then, an object of this invention is to provide the boron nitride dispersion | distribution silicon carbide-carbon composite material which can improve the oxidation resistance of a carbon product, and can suppress fixation of a to-be-processed object.
[0007]
[Means for Solving the Problems]
In order to solve this problem, the present inventors have worked on improving the technology of Japanese Patent Application Laid-Open No. 10-212182 as a prior application, and as a result of earnest research, as a result, boron nitride (hereinafter referred to as the following) is formed on the surface layer of the SiC-C composite layer. It was found that dispersing "BN") was effective, and the present invention was completed.
[0008]
That is, in the BN-dispersed SiC-C composite material of the present invention, the SiC-C composite layer is uniformly formed in the depth direction from the surface of the carbon base material with a thickness of 1 mm or more on the surface layer of the base material made of a carbon material. Te becomes, the SiC-C composite layer has a recess on the surface, successively to the SiC-C composite layer, so that the boron nitride from entering the recess, BN part or the entire surface of the outermost layer of the surface It is a BN-dispersed SiC-C composite material that is dispersed. The manufacturing method of BN dispersion SiC-C composite of the present invention, the BN powder 5 to 15 wt%, 60 to 80 wt% S i powder, _{B 4} A mixed powder sum of C powder is 100 mass%, a slurry consisting of a solvent, is coated on the surface of a substrate, dried, heat treated, a surface portion of said substrate, having a recess on the surface SiC-C becomes a composite layer is formed, so that the boron nitride from entering the recess, BN part or the entire of the surface of the SiC-C composite layers are made by dispersing.
[0009]
Further, in the BN-dispersed SiC-C composite material according to the present invention, a SiC-C composite layer is formed on the surface layer portion of a base material made of a carbon material, and BN enters a recess portion on the surface of the SiC-C composite layer. BN is dispersed and formed at a ratio of 30 to 80% of the surface of the surface layer portion.
[0010]
The base material made of the carbon material used in the present invention is not particularly limited, and examples thereof include high-density isotropic graphite materials. Among these, the average pore radius measured by the mercury intrusion method is 0.00. It is preferable to use a graphite material that is 1 μm or more processed into a product shape.
[0011]
When a graphite material having an average pore radius smaller than 0.1 μm is used as a base material, when the slurry in which Si, B ₄ C and BN are mixed is applied to the base material, the slurry reaches the micropores of the base material. This is not preferable because it hardly penetrates and the slurry coating layer is easily peeled off. The upper limit of the average pore radius of the substrate is not particularly limited, and if the average pore radius is large, the slurry penetrates deeply into the interior of the substrate, and Si in the slurry after the heat treatment The SiC-C composite layer produced by the reaction is formed with a thickness of 1 mm or more uniformly in the depth direction. Thus, since the thickness of a SiC-C composite layer can be 1 mm or more, the oxidation resistance of the base material which consists of carbon materials, such as graphite, can also be improved collectively.
[0012]
The BN-dispersed SiC-C composite material of the present invention is a mixture of Si powder having an average particle diameter of 10 to 50 μm, B ₄ C powder having an average particle diameter of _{4 to} 50 μm, and BN powder having an average particle diameter of 1 to 5 μm. As a solvent to be used, a thermoplastic resin is used to prepare a slurry. Here, the thermoplastic resin used is preferably a thermoplastic resin having a high film-forming property and a low residual carbon ratio. For example, those selected from polyamide imide, polyvinyl alcohol, polycarbodiimide, and polyamide resin are particularly preferable.
In some cases, a solvent may be used to dissolve these thermoplastic resins. The solvent can be appropriately selected from dimethylacetamide, dimethylformamide, dimethylsulfoxide, N-2-pyrrolidone, and the like, thereby allowing the thermoplastic resin to penetrate deeply into the graphite base material.
[0013]
The mixing ratio when mixing the Si powder, the B ₄ C powder and the BN powder is set to 60 to 80% by mass of the Si powder and 15% by mass or less of the BN powder, with the remainder being the B ₄ C powder. It is preferable to mix. If the BN powder exceeds 15% by mass, the SiC-C layer is not formed uniformly and deeply in the depth direction, which is not preferable. Further, if it is less than 5% by mass, the amount of BN dispersedly formed in the dents on the surface of the SiC-C layer is reduced, and the effect of adding BN cannot be obtained sufficiently, and the object to be processed is fixed. Absent. Therefore, the BN powder is preferably 5 to 15% by mass. A thermoplastic resin having a mass of 50 to 100% is mixed with the mixed powder. Here, when the amount of the resin exceeds 100% with respect to the mixed powder, the viscosity of the slurry is lowered, and it is difficult to apply the slurry thickly on the surface of the substrate, which is not preferable because SiC formation on the surface of the carbon substrate is reduced. . On the other hand, if it is less than 50%, the viscosity becomes high, a portion where the slurry is not sufficiently adhered to the surface of the substrate is generated, and a portion where the SiC layer is not formed is not preferable.
[0014]
By mixing B ₄ C powder into the slurry, Si penetrates deeply into the pores of the carbon substrate by some catalytic action, and as a result, the SiC-C layer is formed uniformly and deeply in the depth direction. Can do.
[0015]
The slurry prepared as described above is applied to the entire surface or a necessary portion by an appropriate means such as brushing or spatula coating. Moreover, you may immerse in a slurry. The thickness applied at this time can be any thickness, but is preferably about 0.1 to 2 mm from the surface of the carbon substrate. If the thickness is less than 0.1 mm, the formation of the composite layer is shallow, and if it is applied in a thickness exceeding 2 mm, peeling or the like may occur, which is not preferable. Thereafter, the resin is completely cured by drying at about 80 to 200 ° C. for about 1 to 2 hours. The material thus obtained is subjected to high temperature heat treatment under a non-oxidizing atmosphere pressure of 0.1 MPa or less, preferably 2 kPa or less. By setting the pressure to 0.1 MPa or less, preferably 2 kPa or less, the penetration of molten Si into the substrate is promoted. The treatment temperature is 1500 ° C. or higher, preferably 1600 to 1800 ° C. for 1 to 2 hours. The heating means is not particularly limited and may be performed by an appropriate means. By this operation, the Si component melts, penetrates into the pores of the base material through the carbonized layer of the resin, and reacts with carbon to form SiC. Thereafter, in some cases, the surface deposits are removed.
[0016]
By obtaining the above-described series of treatments, the surface layer of the base material corresponding to the portion where the slurry is applied becomes a dense layer converted into a SiC-C composite layer. This layer is formed at a depth of 1 mm or more substantially uniformly in the depth direction from the surface of the substrate. Then, BN is dispersedly formed on the surface layer portion at a depth of 30 μm or less from the surface. Since BN on the surface enters the dents on the surface of the SiC-C composite layer and is formed continuously from the SiC-C composite layer, the anchor effect acts and adheres firmly. And it does not chemically react with SiC and the carbon base material and is not fixed, but is dispersed and scattered in a fine powder state at a rate of 30 to 80% on the surface of the surface layer part of the SiC-C composite layer. Yes.
[0017]
The BN-dispersed SiC-C composite material of the present invention is formed as described above, and includes hot press die spacers, metal melting crucibles, ceramic sintering crucibles, metal deposition jigs, and continuous casting dies. Even when it is applied as a heat-resistant material used in a jig for heat treatment of various materials including a casting mold or the like, it is possible to suppress sticking to the object to be processed in the contact portion.
[0018]
【Example】
Hereinafter, the present invention will be described specifically by way of examples.
(Example 1)
As a carbon base material, isotropic graphite (manufactured by Toyo Tanso Co., Ltd.) having a bulk density of 1.90 g / cm ³ , an average pore radius of 0.3 μm and a bending strength of 68 MPa, an outer diameter of 100 mm, an inner diameter of about 70 mm, Processed into a 90 mm deep crucible. Next, Si powder (average particle size 40 μm), B ₄ C powder (average particle size 30 μm), and BN powder (particle size 1 to 5 μm) are mixed at a mass ratio of 80: 12: 8, and this mixing is performed. A slurry was obtained by mixing and dispersing in a polyvinyl alcohol (PVA) resin having the same mass as the powder.
[0019]
This slurry was applied to the entire inner surface of the crucible with a brush to a thickness of 1 to 2 mm, the solvent was evaporated in a dryer at 200 ° C. for 1 hour, and further room temperature in a vacuum heating furnace under a nitrogen gas atmosphere of 400 Pa. The temperature was raised from 1 to 1800 ° C. in about 4 hours, held for 30 minutes, then cooled and taken out. After that, by performing this series of treatments, a SiC-C composite material is uniformly formed at a depth of 2 mm from the surface of the graphite base material in the depth direction, and BN is dispersedly formed at a depth of 20 μm on the surface layer. The An ingot was put into this crucible and heated to 1600 ° C. to perform a cast iron dissolution test.
[0020]
FIG. 1 shows a polarizing microscope photograph of the surface of the SiC-C composite material in which BN is dispersed in the surface layer portion. In FIG. 1, the part that appears white is BN. FIG. 1 shows that BN is dispersed and formed on the surface. Thus, since it can be made to disperse | distribute and not be condensed in part, the release property which BN has in a SiC-C composite material can fully be expressed, and adhering of a to-be-processed object is suppressed.
[0021]
(Example 2)
Except mixing the mass ratio of Si powder (average particle size 40 μm), B ₄ C powder (average particle size 30 μm) and BN powder (particle size 1-5 μm) in the slurry at a ratio of 80:10:10 A graphite substrate of the same quality as in Example 1 was processed into the same shape, and a SiC-C composite material was formed on the inner surface of the crucible with a thickness of 1 mm from the surface of the graphite substrate in the same procedure as in Example 1, and 30 μm from the surface. In the same manner as in Example 1, an ingot was placed and a dissolution test was performed.
[0022]
(Example 3)
Except mixing the mass ratio of Si powder (average particle size 40 μm), B ₄ C powder (average particle size 30 μm) and BN powder (particle size 1 to 5 μm) in the slurry at a ratio of 80: 15: 5 A graphite substrate of the same quality as in Example 1 is processed into the same shape, and a SiC-C composite material is formed on the inner surface of the crucible with a thickness of 3 mm from the surface of the graphite substrate by the same procedure as in Example 1, and 15 μm from the surface. In the same manner as in Example 1, an ingot was placed and a dissolution test was performed.
[0023]
(Comparative Example 1)
Without adding BN powder, the mass ratio of Si powder (average particle size 40 μm) and B ₄ C powder (average particle size 30 μm) in the slurry was mixed at a ratio of 80:20, and the same quality graphite as in Example 1 The base material was processed into the same shape, and a SiC-C composite material was formed on the inner surface of the crucible with a thickness of 3 mm from the surface of the graphite base material in the same procedure as in Example 1. The dissolution test was conducted.
[0024]
In spite of 35 melting tests, the crucibles of Examples 1 to 3 had almost no cast iron fixation, and no occurrence of problems causing crucible replacement such as crucible cracking or corrosion due to cast iron was confirmed. It was. On the other hand, in the crucible of Comparative Example 1 in which BN was not dispersedly formed on the surface, the cast iron was fixed in two to three dissolution tests. In this way, a SiC-C composite material is formed on the surface layer of the graphite base material, and further, BN is dispersed and formed continuously from the SiC-C composite material on the surface layer, so that BN is not dispersedly formed. Then, in addition to oxidation resistance, it can have the characteristic which was excellent also in the mold release property of the to-be-processed object.
[0025]
【The invention's effect】
The present invention is configured as described above, and can easily and inexpensively form a silicon carbide-carbon composite material in which boron nitride is dispersed at any location on the surface of the graphite base material. Smooth coated surface with excellent resistance, wear resistance and oxidation resistance can be formed. Moreover, the life extension effect of carbon products for various heat treatments, such as spacers for hot pressing dies, crucibles for metal melting and ceramic sintering, dies for continuous casting, casting molds, etc., can be obtained.
[Brief description of the drawings]
FIG. 1 is a view showing a polarizing microscope photograph of the surface of a BN-dispersed SiC-C composite material.

Claims (8)

On the surface layer of the carbon substrate , a silicon carbide-carbon composite layer is formed with a thickness of 1 mm or more uniformly in the depth direction from the surface of the carbon substrate ,
The silicon carbide-carbon composite layer has a recess on the surface, and boron nitride-dispersed silicon carbide formed by dispersing the boron nitride on the surface of the silicon carbide-carbon composite layer so that boron nitride enters the recess. Carbon composite material. The silicon carbide - the carbon composite layer, before Symbol boron nitride dispersed silicon carbide according to claim 1 dispersed depth of boron nitride is less thick 30μm from the surface - carbon composite material.   3. The boron nitride-dispersed silicon carbide-carbon composite material according to claim 1, wherein a proportion of boron nitride in the surface of the carbon base material is 30 to 80%. Boron powder 5-15 wt% nitride, and 60 to 80 wt% silicic containing powder, and mixed powder sum of the boron carbide powder is 100 mass%, a slurry consisting of a solvent, on the surface of the carbon substrate The silicon carbide-carbon is coated, dried, and heat-treated to form a silicon carbide-carbon composite layer having a dent on the surface of the carbon substrate, and boron nitride enters the dent. table surface boron nitride dispersed silicon carbide, boron nitride is dispersed in the composite layer - the method of producing a carbon composite material. The method for producing a boron nitride-dispersed silicon carbide-carbon composite according to claim 4, wherein the slurry comprises the mixed powder and a solvent having a mass of 50 to 100% of the mass of the mixed powder. The method for producing a boron nitride-dispersed silicon carbide-carbon composite material according to claim 4, wherein the heat treatment is performed at 1500 ° C. or higher in a non-oxidizing atmosphere of 0.1 MPa or lower. The silicon carbide-carbon composite layer is uniformly formed in a depth direction from the surface of the carbon substrate with a thickness of 1 mm or more, and a dispersion depth of the boron nitride is a thickness of 30 μm or less from the surface. The manufacturing method of the boron nitride dispersion | distribution silicon carbide-carbon composite material in any one . The boron nitride-dispersed silicon carbide-carbon composite material according to any one of claims 1 to 3 , which is used as a jig for various heat treatments.

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