JP3449439B2 - Composite sintered body and its use - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates to Si ₃ N ₄ , AlN,
The present invention relates to a composite sintered body obtained by sintering a mixed powder containing Al ₂ O ₃ and BN and its use. Specifically, corrosion resistance suitable for repeatedly measuring the temperature of molten metal with a radiation thermometer,
The present invention relates to a composite sintered body which has excellent heat shock resistance and oxidation resistance and generates little gas, and a protective tube for molten metal temperature measurement which is composed of the composite sintered body.

[0002]

2. Description of the Related Art Conventionally, a method using a consumable immersion thermocouple has been known for measuring the temperature of molten metal (for example, Japanese Patent Publication No. 53).
-47711 publication). Since this thermocouple is a consumable type with a life of 1 to 2 times, it can easily measure temperature, but it can not be used repeatedly, and since the outer cylinder is paper, burned debris at the time of temperature measurement is inside the molten metal. There was a problem such as mixing. Also, there is a technique for continuously measuring temperature by inserting a thermocouple wire into a BN protective tube, but there is a problem that the mounting structure of the thermocouple protective tube becomes complicated.

On the other hand, there are the following publicly known corrosion-resistant members of molten metal composed of Si ₃ N ₄ , AlN, Al ₂ O ₃ and BN. (A) A member for immersing molten metal, which is composed of an inner layer made of silicon nitride or sialon and an outer layer containing boron nitride, silicon dioxide and aluminum nitride as main components, and the inner layer and the outer layer are integrally sintered (special feature: (Kaihei 2-38391).

(B) General formula Si _6-Z Al _Z O _Z N
Β-sialon represented by _8-Z (where Z is 0.8 to 2.0) 40 to 80% by weight, hexagonal boron nitride _{8 to} 40% by weight
And 10 to 40% by weight of zirconia, and a break ring for horizontal continuous casting (Japanese Unexamined Patent Publication No. 2-255248), which is composed of a sintered body in which hexagonal boron nitride and zirconia are dispersed in the β-sialon matrix.

However, in the technique (a), high density (relative density 99%) and high strength (flexural strength 80 kg / mm
² : Sintered bodies at room temperature and 1000 ° C) can be obtained, but on the other hand, the thermal shock resistance ΔT is as low as 600 ° C, which is not suitable for repeatedly measuring the temperature of refractory metals such as cast iron and alloys.

On the other hand, the technique (b) is excellent in corrosion resistance to refractory metals, while the bending strength by the underwater quenching method deteriorates by 10% at 581 to 614 ° C. and the temperature at which it deteriorates by 30% at 618 to 618. Since it was 672 ° C, the thermal shock resistance was insufficient as a protective tube for repeatedly measuring the temperature of the molten metal.

Further, in both the sintered bodies (a) and (b), a large amount of gas is generated when the molten metal comes into contact,
There was a problem that it was not possible to repeat the temperature measurement accurately.

[0008]

As a result of various investigations aimed at solving the above problems, the present inventors have found the following matters and completed the present invention.

(1) The constituents of the sintered body are Si ₃ N ₄ and
The optimum one is obtained by sintering a mixed powder of AlN, Al ₂ O ₃ and BN, and the ratio thereof is Si ₃ N ₄ 30
~ 55 wt%, AlN 5-15 wt%, Al ₂ O ₃ 10
By setting the content to -30% by weight and BN to 20 to 40% by weight, the balance of corrosion resistance against molten metal, thermal shock resistance and oxidation resistance becomes excellent.

(2) From the viewpoint of machinability and thermal shock resistance, the porosity of the sintered body is preferably 20 to 30 %.

(3) Crystalline (L
The use of a) particles containing 50% by weight or more of particles having a size of 800 Å or more provides particularly excellent corrosion resistance and thermal shock resistance to molten metal.

(4) Since the protective tube for measuring the temperature of the molten metal, which is made of the above-mentioned sintered body, has excellent thermal shock resistance, corrosion resistance and oxidation resistance, it has a long life when the temperature is repeatedly measured with a radiation thermometer. Moreover, since the generation of gas is very small, the temperature can be measured accurately.

(5) Even if the protective tube for molten metal temperature measurement composed of the above-mentioned sintered body has a specific shape, it is particularly resistant to thermal shock and load (impact against molten metal) when repeatedly measuring temperature. Since the strength) can be increased, the life can be further extended.

[0014]

That SUMMARY OF THE INVENTION The present invention is, S
i ₃ N ₄ 30 to 55% by weight, AlN _{5 to} 15% by weight, A
l ₂ O ₃ 10 to 30% by weight and crystallite size (La)
BN20 to 4 containing 50% by weight or more of particles of 800 Å or more
It was obtained by sintering a mixed powder consisting of 0 wt% and has a porosity of 20 to 30 % and an oxidation weight loss rate at a temperature of 1200 ° C. of 0.03 mg / cm ² · Hr or less. Corrosion resistant composite sintered body . Also, the present invention
Is a protective tube for measuring the temperature of a molten metal, which is constituted by this composite sintered body . Further, according to the present invention, in this protective tube for measuring temperature of molten metal, a taper is applied from an arbitrary portion of the outer wall to the tip portion, and the inner / outer dimension ratio of the tip portion is 0. It is a protective tube for measuring the temperature of a molten metal, which is characterized by being 0.5 to 0.7.

The present invention will be described in more detail below.

The composite sintered body of the present invention is made of Si₃N_Four, Al
N, Al₂ O₃Obtained by sintering a mixed powder of BN and BN
It is a thing. These components are
presumed to exist in the state of β-sialon and BN
It Of these components, Si ₃N_Four, AlN and Al
₂ O₃Contributes to corrosion resistance and oxidation resistance to molten metal
BN improves thermal shock resistance.

A suitable ratio for achieving a good balance of corrosion resistance, thermal shock resistance and oxidation resistance with respect to molten metal is _{30 to} 55% by weight of Si ₃ N _{4, 5 to} 15% by weight of AlN, Al ₂ O ₃ 10 to 30% by weight and BN 20 to 40% by weight.

If the BN content is less than 20% by weight, the thermal shock resistance is insufficient, the life of the protective tube becomes short, and the machinability deteriorates. Further, if it exceeds 40% by weight, Si ₃ N ₄ , AlN
Since the total amount of Al ₂ O ₃ and Al ₂ O ₃ is relatively insufficient, the corrosion resistance and the oxidation resistance decrease. Above all, as the raw BN powder, 50 particles having a crystallite (La) size of 800 Å or more are used.
By using a material containing at least wt% (including 100%), a composite sintered body having the effect of (3) above can be manufactured.

If Si ₃ N ₄ , AlN and Al ₂ O ₃ are less than the above proportions, the oxidation resistance is lowered, and if it exceeds the above proportions, the corrosion resistance is lowered.

Si ₃ N ₄ , AlN, Al ₂ O ₃ and BN
The particle size of the mixed powder consisting of is preferably a fine powder,
It is preferably 10 μm or less, and particularly preferably 5 μm or less. The mixed powder can be prepared by dry mixing or wet mixing using an organic medium such as alcohol. As the mixer, a ball mill, a vibration mill or the like is used, and a mixing time of 0.5 to 3 hours is suitable.

The mixed powder is hot-pressed or pressure-sintered at a temperature of about 1600 to 1900 ° C. in a non-oxidizing atmosphere such as nitrogen or argon to produce the composite sintered body of the present invention.

Even the composite sintered body produced under the above conditions has various porosities and oxidation weight reduction rates at a temperature of 1200 ° C. depending on the composition of the mixed powder and the sintering conditions. The composite sintered body of the present invention has a porosity of 20 to 30.
% Decrease in oxidation weight at a temperature of 1200 ° C. of 0.03
It is less than or equal to mg / cm ² · Hr.

If the porosity is less than 20% , the thermal shock resistance and machinability deteriorate, and if it exceeds 30% , the corrosion resistance to molten metal deteriorates. On the other hand, when the oxidation weight loss rate at a temperature of 1200 ° C. exceeds 0.03 mg / cm ² · Hr, the amount of gas generated increases, and it becomes difficult to accurately measure the temperature of the molten metal.

The oxidation weight loss rate (mg / cm ² · Hr) at a temperature of 1200 ° C. in the present invention is 25 × 13 ×
It can be calculated by measuring the weight before and after cooling a 1 mm specimen in an air atmosphere furnace having a temperature of 1200 ° C. for 1 hour.

The mechanism of reduction of the oxidized weight and gas generation of the composite sintered body can be explained as follows.
That is, BN should be converted to B ₂ O ₃ and the weight should be increased by the reaction of 4BN + 3O ₂ → 2B ₂ O ₃ + 2N ₂ , but the B ₂ O ₃ produced is actually gasified at a temperature of about 900 ° C. or higher. Therefore, the weight of the composite sintered body is reduced.

The application of the composite sintered body of the present invention is a jig for molten metal treatment such as a casting nozzle, a break ring, a melting crucible, a thermocouple or a protective tube for temperature measurement. The characteristics of excellent corrosion resistance to molten metal, thermal shock resistance, oxidation resistance, and less gas generation are particularly suitable as a protective tube for measuring temperature of molten metal.

The cross-sectional shape of the protective tube for measuring the temperature of the molten metal of the present invention may be any of a circular shape, an elliptical shape, a rectangular shape, etc., as described in JP-A-55-160401, but it is preferable. The outer wall is tapered from any part to the tip, and the inside / outside ratio of the tip is 0.5-
It is 0.7, which can further increase the thermal shock resistance of the tip of the protective tube and the withstand load near the taper start portion of the protective tube when the temperature is repeatedly measured.

If the inner dimension / outer dimension ratio of the tip portion is less than 0.5, the wall thickness becomes too thick and the thermal response speed deteriorates.
If it exceeds 7, the wall thickness becomes too thin and the withstand load decreases.
The taper applied to the outer wall is formed from any portion of the outer wall, that is, from the upper opening or any middle portion to the tip portion, but preferably 30 to 70% of the protective tube length, especially 4
That is, it is formed from the portion of 0 to 60% to the tip portion. With respect to the degree of taper inclination, it is preferable that the ratio of the wall thickness of the taper start portion to the wall thickness of the protective tube front end portion (taper end portion) is 1.5 to 2.0. When this ratio is less than 1.5, the withstand load is insufficient and the area near the taper start portion is easily broken, and when it exceeds 2.0, the wall thickness of the taper start portion becomes large and the thermal shock resistance deteriorates.

The protective tube having such a shape is used by immersing it in molten metal. The immersion depth is 30 to 70% of the length of the protective tube, especially 40 to 60%,
Particularly, it is preferable that the molten metal surface is near the taper start portion.

[0030]

EXAMPLES The present invention will be described more specifically with reference to Examples and Comparative Examples.

[0031] Example 1 Si ₃ N ₄ powder (average particle size 1 [mu] m), AlN powder (average particle size 10 [mu] m), particles 80 weight Al ₂ O ₃ powder (average particle size 0.3 [mu] m) and BN powder (LA900 Å %, La600 Å
20% by weight of the above particles and having an average particle size of 10 μm) were mixed in a ratio shown in Table 1 to prepare a mixed powder. This is filled in a graphite die and the temperature is 1800 ° C. and the pressure is 100 kg / cm.
Hot press sintering to composite sintered body ² (diameter 250mm
X height 200 mm) was produced. When this component was analyzed by X-ray diffraction, BN and β sialon were identified.

Next, a protective tube (outer diameter 16
mm, inner diameter 10 mm, length 180 mm),
Relative density (%) by Archimedes method and weight loss rate at the above temperature of 1200 ° C (mg / cm ² · Hr)
Was measured as oxidation resistance. Is the porosity (%) 100%?
It is the value obtained by subtracting the relative density (%).

Further, the protection tube is made of cast iron having a temperature of 1500 ° C.
The operation of immersing for 0 seconds (immersion depth of 80 mm) and measuring the temperature was repeated, and the number of times of repeated use (life of protective tube) when cracks occurred or melted was measured. Also,
Whether or not gas was generated during the temperature measurement was observed. The results are shown in Table 1.

Examples 2 to 3 A protective tube was manufactured in the same manner as in Example 1 except that the ratio of the mixed powder was as shown in Table 1.

Example 4 A protective tube was manufactured in the same manner as in Example 1 except that the hot pressing temperature was set to 1700 ° C.

Example 5 Instead of hot press sintering, pressureless sintering (slip-cast molding of mixed powder, which was carried out under nitrogen atmosphere at temperature 1850)
A protective tube was manufactured in the same manner as in Example 1 except that the protective tube was sintered.

Example 6 A protective tube was produced in the same manner as in Example 1 except that the outer wall of the protective tube was tapered from the position of the upper opening of 100 mm to the tip thereof. The taper was inclined such that the ratio of the wall thickness at the taper end portion to the wall thickness at the taper end portion was 1.7.

Comparative Examples 1 to 4 A protective tube was manufactured in the same manner as in Example 1 except that the ratio of the mixed powder and the hot pressing temperature were set as shown in Table 1.

[0039] Comparative Example 5 crystallite size of (La) is 900 Å particles 20 weight percent,
A protective tube was manufactured in the same manner as in Example 1 except that BN powder having a particle diameter of 600 Å 80% by weight and an average particle diameter of 10 μm was used.

[0040]

[Table 1]

[0041]

According to the present invention, there is provided a composite sintered body which has an excellent balance of corrosion resistance against molten metal, thermal shock resistance, and oxidation resistance, and produces little gas, and a protective tube for measuring the temperature of molten metal.

Continuation of the front page (56) Reference JP-A-4-280887 (JP, A) JP-A-61-72605 (JP, A) JP-A-62-176904 (JP, A) JP-A-62-163940 (JP , A) Ceramic Engineering Handbook, Gihodo Publishing Co., Ltd., April 10, 1989, p. 891-893 (58) Fields investigated (Int.Cl. ⁷ , DB name) C04B 35/584 G01K 1/08

Claims (3)

(57) [Claims] 1. Si ₃ N ₄ 30 to 55% by weight, AlN 5
To 15%, obtained by sintering Al ₂ O ₃ 10 to 30% by weight and size (La) mixed powder consisting of 800 Å or more particles from BN20~40 wt%, including 50% or more by weight of crystallites Which has a porosity of 20 to 30 % and a temperature of 12
Oxidation weight loss rate at 00 ° C 0.03 mg / cm ² ·
A corrosion-resistant composite sintered body, which is Hr or less. 2. A protective tube for measuring the temperature of a molten metal, comprising the composite sintered body according to claim 1. 3. A taper is applied from an arbitrary portion of the outer wall to the tip portion, and the inner / outer dimension ratio of the tip portion is 0.5 to 0.7. Protective tube for measuring temperature of molten metal.