JPH0553752B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a setter for heat treatment such as shelf boards used when performing ceramic firing treatment or metal heat treatment.

[Conventional technology]

Conventional setters for heat treatment of this type include those made of sintered oxides such as alumina and mullite (hereinafter referred to as "first conventional setter"), and those made of ceramic fiber (hereinafter referred to as "second conventional setter"). ) and silicon carbide are known. Such silicon carbide materials include recrystallized materials (hereinafter referred to as "third conventional setter");
There are those bonded with oxides such as silicate (hereinafter referred to as "fourth conventional setter") and those bonded with Si ₃ N ₄ (hereinafter referred to as "fifth conventional setter").

[Problems to be Solved by the Invention] However, since the first conventional setter has a high density, it has a large heat capacity and is inferior in thermal efficiency to the object to be fired. Further, thermal shrinkage and creep are likely to occur due to high temperature heating. Moreover, since it has poor spalling resistance, it is difficult to rapidly heat and cool it, and it is difficult to shorten the firing cycle. In addition, since it is a heavy object with high density, it is inferior in handling and workability.

The second conventional setter is designed to improve spalling resistance and reduce weight, but because it is inferior in strength, it is a thick setter, and the setter occupies less space in the furnace. As a result, the amount of material to be fired decreases.

The third to fifth conventional setters are excellent in heat resistance, spalling resistance, high hot strength, etc.
Although the third conventional setter can be manufactured with high purity, it is extremely expensive.

In addition, although the fourth and fifth conventional setters are inexpensive, they emphasize oxidation resistance, making the constituent particles coarser and having a higher density (2.4 to 2.6 g/cm ³ ), so they can be used repeatedly. There is a problem with spalling resistance. Furthermore, since the constituent particles are coarse, the strength is insufficient and it is difficult to make it lighter and thinner.

The purpose of the present invention is to solve all of the problems with conventional setters, and to provide a setter for heat treatment that has excellent oxidation resistance, creep resistance, and strength, and can be made lighter and thinner. be.

[Means to solve the problem]

The setter for heat treatment of the present invention, which solves this problem, uses 20% α-type silicon carbide fine particles with a particle size of 1 μm or less.
Obtained by molding and firing a raw material powder containing at least 50% by weight (more preferably at least 50% by weight), with the remainder being α-type silicon carbide coarse particles with a particle size of 1 to 20 μm and 5% or less by weight of unavoidable impurities. It is made of porous silicon carbide sintered body.

Specifically, the porous silicon carbide sintered body that forms the main body of the setter is formed into a desired shape by adding appropriate shaping aids to the raw material powder, then subjected to wax removal treatment, and then fired. obtained by. The setter of the present invention may be constructed using only this silicon carbide sintered body, or the setter may be constructed using this silicon carbide sintered body as an aggregate. For example, a setter is constructed by forming an alumina coating layer on the surface of a silicon carbide sintered body.

As the raw material powder, for example, a mixture of 50% by weight of polishing powders GC#8000 (average particle size 1 μm) and GC#4000 (average particle size 3 μm) manufactured by Fujimi Abrasives Co., Ltd. is used. Such raw material powder contains unavoidable impurities such as SiO ₂ , carbon, and Fe ₂ O ₃ , but the amount of such impurities is set to 5% by weight or less as described above.

As a molding aid, for example, 2% by weight of PEG
and methanol in which 1% by weight of stearic acid is dissolved.

The firing process is carried out in a vacuum atmosphere, inert atmosphere or
The firing is carried out in an atmosphere of CO, _N2, etc., and the firing temperature is preferably 1600 to 2200°C.

The silicon carbide sintered body obtained as above is
It is preferable that the material has a density of 1.6 to 2.3 g/cm ³ , a porosity of 30 to 50%, and a high anti-deposition strength of 500 to 2500 Kg/cm ² . Moreover, this silicon carbide sintered body is a self-assembly body, and preferably has a SiC crystal structure with a low aspect ratio of 2 to 20 μm and fine pores of 1 to 5 μm.

[Effect]

Silicon carbide fine particles with a particle size of 1μm or less and particles with a particle size of 1~
Since silicon carbide coarse particles of 20 μm are mixed, the packing density at the molding stage is increased and the degree of contact between the particles is increased. Therefore, in the firing stage, sintered particle growth between fine particles and bonding between coarse particles are promoted. In this case, the only effect is the relaxation of surface energy due to bonding of crystal grains, and shrinkage and
Since it does not have a driving force for densification, the pores between grains are dispersed in a fine red state.

Therefore, although the silicon carbide sintered body has extremely low density, it has high strength. That is,
High strength is achieved by the self-bonding force due to coarse growth of α-type silicon carbide fine particles and the self-bonding force of silicon carbide generated by the following reaction.

SiO ₂ +SiC→2SiO↑+C SiO+2C→SiO+CO↑ Also, this silicon carbide sintered body has heat resistance, oxidation resistance,
Creep resistance can be significantly improved.

〔Example〕

Polishing powder GC#8000 (average particle size) manufactured by Fujimi Abrasives Co., Ltd.
1μm) and 50% by weight of the company's polishing powder GC# 4000 (average particle size 3μm) were placed in a ball mill, and methanol in which 2% by weight of PEG and 1% by weight of stearic acid were dissolved in this raw material powder was added. The same amount (100% by weight) as the raw material powder was added, and these were stirred and mixed. Note that the amount of unavoidable impurities in the raw material powder is 5% by weight or less.

Next, this slurry was dried and granulated using a spray dryer, and the cavity size was 40 mm x 90 mm.
Pressure molding was performed using a mold with a molding pressure of 1000 kg/cm ² to obtain a molded product measuring 3 mm x 40 mm x 90 mm.

Then, this molded body was dewaxed in the air at 500°C, and then fired at 1700°C for 1 hour in a vacuum atmosphere firing furnace to obtain a porous silicon carbide sintered body, that is, a setter according to the present invention. Ta. This silicon carbide sintered body had a density of 2.00 g/cm ³ and a shrinkage of 0.1% was observed. Moreover, the constituent particle diameter was 5 to 15 μm, and the pore diameter was 1 to 2 μm.

In addition, as a comparative example, a setter having the same dimensions as the setter was obtained.

Setter polishes the raw material powder above with GC#8000
This is a silicon carbide sintered body obtained in the same manner as in the above example except that it consisted of only This silicon carbide sintered body had a density of 1.98 g/cm ³ and a shrinkage of 2.1% was observed. Further, the constituent particle diameter was 1 to 2 μm, and the pore diameter was 1 μm or less.

Setter polishes the raw material powder above with GC#4000
This is a silicon carbide sintered body obtained in the same manner as in the above example except that it consisted of only This silicon carbide sintered body has a density of 2.00, which is the same as the setter.
g/cm ³ , but the interparticle bonds are extremely weak and the bending strength is about 0.5 to 3 Kg/mm ² .
It was clearly not suitable as a setter.

The setter is obtained by cutting a commercially available setter corresponding to the fourth conventional setter mentioned at the beginning into the same size as each setter described above.

Comparative tests were then conducted on the oxidation resistance, etc. of each setter. As for the setter, as mentioned above, it was clearly not suitable as a setter, so it was decided not to conduct such a test.

That is, each setter is set in an oxidation furnace and heated to 1400℃ at a heating rate of 500℃ per hour.
The sample was heated to a temperature of 100.degree. C., maintained at that temperature for 2 hours, allowed to cool naturally, and then the heating and cooling steps were repeated, and the oxidation increase rate and the like were measured for each cycle.

As a result, as for the setter, as shown by the solid line in Figure 1, the setter is about 10
% increase in oxidation was observed, but no creep, cracks, etc. were observed even after 30 cycles.
It was confirmed that it showed extremely good results as a setter.

Regarding the setter, as shown by the broken line in Figure 1, creep occurs after 3 cycles.
Cracking occurred after 5 cycles. Furthermore, an increase in oxidation of 25% was observed after 5 cycles, indicating that the oxidation resistance was poor. By the way, when the raw material powder does not contain coarse SiC particles such as in a setter, the packing density at the molding stage is low and the degree of contact between particles is small. As a result, bonding of crystal grains and grain growth are suppressed, and the constituent particles of the sintered body become smaller and have a larger surface area, resulting in lower resistance to oxidation. In such a case, increasing the firing energy also promotes particle growth and improves oxidation resistance, but has the disadvantage of increasing energy cost.

As for the setter, as shown by the chain line in FIG. 1, the oxidation increased by 15% after 5 cycles, and the surface clearly became glassy. In addition, creep occurred after 30 cycles.

Regarding the setter, it was set in an oxidation furnace and 100 g of silicon carbide sintered body was placed on it, and heated under the same conditions as above.
When cooling was repeated, no creep occurred even after 20 cycles, showing excellent creep resistance. It was also confirmed that the thermal efficiency of the silicon carbide sintered body was extremely high.

Furthermore, from each setter, 3mm x 4mm
When test pieces were cut out to a size of 40 mm and the hot strength (flexural strength) of each test piece was measured, the results shown in FIG. 2 were obtained. That is, the setter exhibited a high strength of 17 to 23 kg/mm ² (solid line in Figure 2). In Setter, the value is slightly lower (15~
20Kg/mm ² ) (dashed line in the same figure), but the setter showed an extremely low value (dashed line in the same figure), indicating that the strength was inferior.

〔Effect of the invention〕

As can be easily understood from the above explanation, the setter for heat treatment of the present invention has low density, high porosity, and high strength, and can be made lighter, thinner, and lower in price. It has excellent hardness, creep resistance, and spalling resistance. Therefore, according to the setter of the present invention, the packing efficiency and thermal efficiency of the firing furnace can be greatly improved, and firing and heat treatment can be performed extremely efficiently.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the oxidation resistance test results, and FIG. 2 is a graph showing the hot strength test results.

[Claims]

1. A method in which a molded body containing silicon nitride as a main component is primarily sintered and then secondary sintered at a higher temperature and pressure than the primary sintering, the primary sintering being performed at a temperature of 1500 to 1800°C in a nitrogen atmosphere of 10 atmospheres or less. A method for producing a silicon nitride sintered body, characterized in that the relative density in the primary sintering step is 88% or more, and the secondary sintering is performed at a temperature exceeding 1800°C at a pressure exceeding 10 atmospheres.