JPH06263544A - Sialon-based composite sintered compact and its production - Google Patents

Abstract

PURPOSE:To provide a dense sialon-based composite sintered compact, having a sufficient strength and excellent in thermal shock resistance and corrosion resistance to molten metals and a method for producing the sintered compact. CONSTITUTION:This dense sialon-based composite sintered compact is composed of the following compositions (1) to (4) and comprises fine BN, having <=2mum size and uniformly dispersed in a sialon matrix: (1) 30-70wt.% sialon composition composed of Si3N4, AlN, Al2O3 or Si3N4, AlN, Al2O3 and SiO2 and expressed by the formula Si6-ZAlZOZN8-Z [1<=Z<=3], (2) 20-70wt.% boron nitride composed of crystallites having 50-150Angstrom diameter thereof, (3) 0.1-10wt.% CaO or SrO component and (4) 0.1-5wt.% at least one or more oxides of Y and lanthanide- based metallic elements.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sialon composite sintered body which is dense and has sufficient strength, and which is excellent in thermal shock resistance and corrosion resistance against molten metal, and a method for producing the same. In particular, the present invention is mainly a variety of nozzle members for molten metal, which requires severe heat load and corrosion resistance as a field of use,
Break ring for horizontal continuous casting of steel and protection tube for temperature measurement,
The present invention relates to a sialon-based composite sintered body suitable for various burner parts and the like, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, for BN-based composite ceramics, hot pressing has been carried out by adding various sintering aids because BN is a material that is difficult to sinter. A manufacturing method by an atmospheric pressure sintering method is also implemented.

However, although a dense sintered body can be obtained by the conventional hot pressing method, BN is a plate-like crystal having a layered structure and has an orientation in the molding direction. However, there is a problem that it is difficult to obtain uniform sintered body characteristics. Further, in the conventional manufacturing method by the above reaction sintering and atmospheric pressure sintering, it is difficult to obtain a dense sintered body, and there is a problem in strength characteristics and durability in an environment where high corrosion resistance to molten metal is required. .

In addition, in Japanese Patent Laid-Open No. 3-177361, β-sialon powder is first synthesized using silicon diimide, and using this, a composite material with BN (β-sialon-boron nitride-based composite sintered body) is prepared. ) Is described, a porous sintered body having a relative density of 80% or less is obtained when BN is 20% or more. Further, Japanese Patent Application Laid-Open No. 60-145963 describes a sialon-boron nitride composite sintered body produced by the reaction sintering method, but the porosity of 20% is obtained even by the high temperature treatment by the reaction sintering method. The above-mentioned sintered body can be obtained, and a material having small thermal shock resistance and strength characteristics can be obtained.

Further, since a composite material with BN is generally a porous material, a material whose surface is coated with alumina or the like has been conventionally proposed (see Japanese Patent Laid-Open No. 4-280887). Furthermore, as a Si ₃ N ₄ -BN material, a specific surface area of 100 m ² /
It is also proposed to use a fine BN of g or more and to add about 15% of cordierite as a sintering aid to obtain a composite sintered body having a thermal shock resistance (△ Tc) of 1200 ° C or more that is strong against thermal shock. However, the Si ₃ N ₄ —BN system containing cordierite has a problem in being applied to a member that requires corrosion resistance at high temperatures.

[0006]

By the way, in the conventional composite sintered body containing BN, as mentioned above, it becomes a porous material with the addition of BN, and a material satisfying strength, thermal shock resistance and corrosion resistance is obtained. Not not. Therefore, the present inventors, in the composite sintered body containing BN, is a dense, strength, thermal shock resistance, the technical problem to obtain an excellent corrosion resistance, as a means to achieve this problem, nitriding The present invention was completed as a result of attempting to improve the characteristics by forming a substitutional solid solution with an oxide in a substance and thereby forming a composite of sialon and BN.

[0007] That is, the present invention is to provide a dense sialon-based composite sintered body in which fine BN having extremely little orientation is uniformly dispersed in a sialon matrix, and a method for producing the same. ). Another object of the present invention is to provide a sialon-based composite sintered body that is dense and has sufficient strength, and is excellent in thermal shock resistance and corrosion resistance against molten metal, and a method for producing the same.

[0008]

The present invention has a technical object to obtain a dense sintered body in which fine BN having extremely little orientation is uniformly dispersed in a sialon matrix. The present invention is characterized in that BN of 50 to 150 angstrom is used and that a predetermined amount of CaO or SrO component is blended, thereby providing the above-mentioned target sintered body.

That is, the sialon-based composite sintered body of the present invention has the following characteristics: "(1) Si ₃ N ₄ , AlN, Al ₂ O ₃ or Si ₃ N ₄ , AlN, Al ₂ O ₃ ,
Sialon composition consisting of SiO ₂ and represented by Si _6-Z Al _Z O _Z N _8-Z (1 ≦ Z ≦ 3) 30 to 70% by weight, (2) From crystallite size 50 to 150 angstrom 20-70% by weight boron nitride, (3) Ca
0.1 to 10% by weight as an O or SrO component, (4) Y and at least one oxide of a lanthanide metal element 0.1 to 5
% By weight, dense and in a sialon matrix
A sialon-based composite sintered body, characterized in that fine BN of 2 μm or less is uniformly dispersed. Is the gist.

The present invention also provides, as a method for producing the above sintered body, "(1) Si ₃ N ₄ , AlN, Al ₂ O ₃ or Si ₃ N ₄ , AlN, Al.
₂ O ₃ , SiO ₂ and the above raw material powder mixture which produces 30 to 70% by weight of a sialon composition represented by Si _6-Z Al _Z O _Z N _8-Z (1 ≦ Z ≦ 3), (2 ) 20-70% by weight of boron nitride having a crystallite size of 50-150 Å, (3) as CaO or SrO component
0.1 to 10% by weight, (4) 0.1 to 5% by weight of at least one oxide of Y and a lanthanide-based metal element are uniformly mixed, and this mixture is subjected to isostatic pressing, die molding, and cast molding. , Injection molding, etc.
The method for producing a sialon-based composite sintered body, which comprises performing atmospheric pressure sintering or gas pressure sintering at ˜1850 ° C. in an N ₂ or Ar atmosphere. Is the gist.

The present invention will be described in detail below. Si ₃ N ₄ , AlN, Al ₂ O ₃ was used as a starting material without using sialon powder.
Or Si ₃ N ₄ , AlN, Al ₂ O ₃ , in the sialon-based material using the powder of SiO ₂ , a liquid phase is generated during the formation process, Si _6-Z Al _Z O _Z N _8-Z The represented Sialon composition is produced. In the present invention, for the purpose of improving characteristics and densification, the above raw material powder for producing a sialon composition is used as a starting raw material, and the above-mentioned dissolution and precipitation reaction at the time of producing the sialon composition is utilized.

Further, in the present invention, Ca is an essential component.
The reason for using the oxide containing O or SrO, Y ₂ O ₃ and the lanthanide series is to increase the dissolution phenomenon of sialon and to increase the amount of liquid phase in the sintering process.
As a result, increasing the wetting of BN fine crystal grains in the liquid phase,
In addition, it suppresses the growth of BN crystal grains, and the BN fine crystal grains are uniformly dispersed in the sialon matrix by the subsequent precipitation reaction of the sialon composition, that is, crystallization. A sialon composite sintered body is obtained.

The BN raw material powder for this purpose has a crystallite diameter of 50 to 150 angstroms and a specific surface area of 80 to 300.
The use of BN having a small m ² / g orientation is an essential constituent feature of the present invention and is a feature of the present invention. Even if the crystallite size is larger than 150 angstroms, or too small than 50 angstroms, inhibition of sinterability due to plate-like crystals occurs, and because it acts as agglomerated particles,
It is not preferable because the effect of improving the properties is not recognized (see Comparative Examples Nos. 13 and 15 in Table 1 below). In addition, there is a problem that it is difficult to handle at 50 angstroms or less.

The sialon-based composite sintered body of the present invention comprises (1)
Si ₃ N ₄ , AlN, Al ₂ O ₃ or Si ₃ N ₄ , AlN, Al ₂ O ₃ , SiO ₂ Si _6-Z Al _Z O _Z N _8-Z (1 ≦ Z ≦ 3) Sialon composition: 30 to 70% by weight, (2) BN having a crystallite size of 50 to 150 angstroms: 20 to 70% by weight, (3) as a CaO or SrO component
0.1-10% by weight, (4) One or more oxides of Y and lanthanide elements: 0.1-5% by weight, with a fine BN of 2 μm or less uniformly dispersed in the sialon matrix. Is. In the present invention, if the above composition conditions are not satisfied, the composite effect is small, and a good sintered body excellent in strength, thermal shock resistance and corrosion resistance cannot be obtained.

In the sialon-based composite sintered body of the present invention, the Z value of the sialon composition Si _6-Z Al _Z O _Z N _8-Z is preferably 1 ≦ Z ≦ 3. When the Z value is less than 1, it is close to Si ₃ N ₄ and the corrosion resistance decreases, which is not preferable (Comparative Example No. 1
On the other hand, when the Z value exceeds 3, on the other hand, it becomes difficult to suppress the composition, and the strength and thermal shock resistance decrease, and the coefficient of thermal expansion increases, which is not preferable.

Further, in the present invention, the reason why the sialon content is 30 to 70% by weight and the BN content is 20 to 70% by weight is because the strength of a fine BN homogeneous dispersion in a sialon matrix is high. This is to maintain excellent sinterability such as heat shock resistance and corrosion resistance. That is, the BN content is 20
If it is less than wt%, sufficient thermal shock resistance cannot be obtained (see Table 1 below).
On the other hand, when the BN content exceeds 70% by weight, sufficient strength cannot be obtained due to a decrease in sinterability.

The CaO or SrO component as an additive lowers the melting temperature of the starting material which produces sialon,
It exhibits an action (role) of wetting the N crystal interface, and as the CaO component, various raw materials such as Ca oxides, carbonates, and hydroxides that generate CaO by heating can be used. Similarly, various raw materials that heat the SrO component to produce SrO can also be used. Also, the amount added is 10% by weight.
If the amount exceeds the above range, the thermal shock resistance and the characteristics at high temperature deteriorate, so addition of 10% by weight or less is desirable.

Next, a method of manufacturing the sialon-based composite sintered body of the present invention will be described. In the present invention, as a raw material (starting raw material) for producing the sialon composition Si _6-Z Al _Z O _Z N _8-Z (1 ≦ Z ≦ 3), Si ₃ N ₄ , AlN, Al ₂ O ₃ or Si ₃ N ₄ , Al
N, Al ₂ O ₃ , and SiO ₂ are used, and the raw materials are blended so as to produce a sialon composition having a predetermined Z value. To this raw material powder mixture, BN powder having a crystallite size of 50 to 150 angstrom, CaO or SrO component and Y or lanthanide metal oxide (for example, Y ₂ O ₃ , Yb ₂ O ₃ etc.) were added, and ethanol was added. After uniformly pulverizing and mixing in an organic solvent or aqueous solution such as the above with the addition of a binder, it is dried and granulated to obtain a forming raw material.

Using this molding raw material, a molded product is produced by isostatic pressing, molding, casting, injection molding or the like. Sintering of this molded product can be carried out at 1650 to 1850 ° C. in an N ₂ atmosphere by an atmospheric pressure sintering method and an atmosphere (N ₂ , Ar) gas pressure sintering alone or in combination. In the temperature decreasing process after sintering, the grain boundary phase can be crystallized by holding it at 1300 to 1500 ° C for about 24 hours.

As a result of identification by X-ray diffraction, it was confirmed that the obtained sialon-based composite sintered body was composed of β sialon phase and BN as main constituent phases and a slight amount of grain boundary glass phase. In addition, from the measurement results of the lattice constant of the sialon phase by the X-ray diffraction method, the composition has a Z value lower than that of the raw material by 0.2 to 0.3, but it is confirmed that the sialon is surely generated by the melt extrusion reaction. did it. In addition, SEM (Scannin
As a result of analysis by g Electron Microscope), it was confirmed that fine BN crystal grains of 2 μm or less were uniformly dispersed in the sialon matrix and had a dense structure (see FIG. 1 described later).

[0021]

EXAMPLES Examples of the present invention will be given below together with comparative examples.
The present invention will be described in more detail. Example 1 Sialon composition Si _6-Z Al _Z O _Z N _8-Z (1 ≦ Z ≦
As starting materials for 3), Si ₃ N ₄ (average particle size: 0.8 μm, O ₂ content: 1.0% by weight), AlN (average particle size: 1.0 μm, O ₂ content: 1.5% by weight), Al ₂ O ₃ (purity: 99.9%, average particle size: 0.5 μm), and SiO ₂ (purity: 99.5%, average particle size: 0.5 μm) were used. In addition, as CaO component ・ CaCO ₃ (purity: 99%, average particle size: 0.5 μm) is used, and as rare earth oxide ・ Y ₂ O ₃ , Yb ₂ O ₃ (both purity: 99.5%, average particle size : 0.5
μm), was used.

First, BN powder having a crystallite size shown in Table 1, the above CaCO ₃ and a sintering aid (Y ₂ O ₃ , Yb ₂ O ₃ ) were blended with the starting material of the above Sialon composition to prepare a Sialon composition. object,
A predetermined raw material mixed powder composition shown in Table 1 consisting of boron nitride, CaCO ₃ and a sintering aid was prepared. In addition, CaO in Table 1
The additive weight% of the components and the sintering aid is the sialon composition and the BN
And the total amount of 100 parts by weight are% by weight.

This raw material mixed powder composition was uniformly blended in an alcohol for 24 hours with a ball mill made of Si ₃ N _{4 and then} sprayed.
A granulated product was obtained using a dryer. Next, this granulated product was molded at a pressure of 1.5 t / cm ² by a hydrostatic press, and then at 1750 ° C.
A sialon-based composite sintered body was obtained by pressureless sintering for / 5 h.

The obtained sintered body was subjected to a density characteristic (relative density%), a bending test (three-point bending strength at room temperature according to JIS-R1601), and a thermal shock resistance evaluation test by an underwater quenching method. Furthermore, a crucible with an outer diameter of φ30 × 30t-inner diameter of φ20 × 20t is manufactured, and φ18 × 15t of SUS 304 is put into this crucible, and the temperature is 1600 ° C.
The corrosion resistance was evaluated in a high frequency furnace in an Ar atmosphere for / 2 h. The results are shown in Table 1. No. 1 in Table 1
11 to 11 are examples, and Nos. 12 to 17 are comparative examples.

[0025]

[Table 1]

From the above Table 1, N which is the composition range of the present invention is shown.
o.1-11 sialon composite sintered body (Example of the present invention)
It can be seen that indicates excellent sintered body properties.

On the other hand, in Comparative Examples No. 12 and No. 16,
Since it did not contain a CaO component, it had low density, low strength, and poor corrosion resistance. Also,
In Comparative Examples No. 13 and No. 15, 200 angstroms (No. 13) and 180 angstroms outside the range of "BN powder having a crystallite size of 50 to 150 angstroms" which is a feature of the present invention. (No. 15) BN powder was used, which had low density, low strength, low thermal shock resistance, and poor corrosion resistance.

Further, in Comparative Example No. 14, a sialon having a Z value outside the composition range of the present invention of 0.5 and having a composition ratio of sialon and BN of 80% by weight: 20% by weight,
Although this sintered body had high density and high strength, it had poor thermal shock resistance and poor corrosion resistance. In Comparative Example No. 17, the composition ratio of sialon and BN, which is out of the composition range of the present invention, is 85% by weight: 15% by weight, which has high density and high strength, and also has corrosion resistance. Good, but poor in thermal shock resistance.

Next, SEM analysis was performed on each of the sintered bodies obtained in No. 2 (Example of the present invention) and No. 15 (Comparative Example) in Table 1. The analysis results are shown in Figure 1 (No. 2 SEM organization chart) and Figure 2 (No. 15 SEM organization chart). As shown in Table 1, No. 2 which is an example of the present invention uses BN having a crystallite diameter of 65 Å, while No. 15 which is a comparative example is 180 This is an angstrom type.

As is clear from FIG. 1, No. 2 is dense and it is recognized that BN having a size of 1 μm or less is uniformly dispersed in the sialon matrix. As a result, the strength and thermal shock resistance are improved. Was also excellent. On the other hand, as is clear from FIG. 2, in No. 15 which is a comparative example, the BN crystal in the sialon matrix was as large as 3 μm, and it was recognized that the BN portion was porous, and The relative density is as low as 75%, and as a result, the mechanical properties are considered to be degraded.

(Example 2) A sialon composition (Z = 2) was produced. The starting material shown in Example 1 was 30% by weight of BN, 5% by weight of Y ₂ O ₃ as a sintering aid, and CaO ( (Added with CaCO ₃ ) was blended at a ratio of 5% by weight to prepare a raw material mixed powder composition.

This raw material mixed powder composition was kneaded with water as a solvent in a vibration mill for 5 hours and then dried at 120 ° C. to obtain a raw material for molding. Next, after putting this molding raw material in a mold and molding at a pressure of 1.5 t / cm ² using a rubber press,
It was fired at 1750 ° C by an atmospheric pressure sintering method. For comparison, Ca
Firing was performed in the same manner as above except that CO ₃ was not added to obtain a sintered body.

The density and the porosity of the obtained sintered body were measured, and the bending strength and the thermal shock resistance (ΔTc) by the underwater quenching method were determined. The results are shown in Table 2. Further, the corrosion resistance of the sintered body to molten metal was tested using a high temperature microscope. The test method is as follows. The sintered body was processed into a plate shape of 10 × 3 tmm to prepare a sample, and □ 2 × 2 t SUS 304 was placed on the sample.
After depressurizing the sample at room temperature, the morphological change was observed with a telescopic microscope while heating in Ar gas. 1500 ℃ in Ar atmosphere
Up to 1500 ° C and hold for 2 hours, and the sample (sintered body) and S
The contact angle (wettability) with US 304 was measured. The results are shown in Table 2.
Shown in.

[0034]

[Table 2]

As is clear from Table 2 above, the addition of 5% of CaO densified the structure and improved the flexural strength and thermal shock resistance. Further, regarding the measured values of the contact angle in Table 2, comparing the CaO-free sintered body (Comparative Example) and the sintered body with CaO 5% added (Example 2), the former shows that
The contact angle with SUS 304 is 80 degrees, whereas the latter CaO5
%, The sintered body was added at 135 ° C., and there was a significant difference in the wettability with respect to SUS 304. This difference in wettability is due to SU
It shows the difference in corrosion resistance to S 304, and therefore C
This shows that the sintered body to which aO is added has excellent corrosion resistance to SUS 304.

Example 3 Sialon Composition Si _6-Z Al _Z O _Z
As a starting material for N _8-Z (1 ≦ Z ≦ 3), Si ₃ N ₄ (average particle size: 0.8 μm, O ₂ content: 1.0% by weight), AlN (average particle size: 1.0 μm, content) O ₂ amount: 1.5% by weight) ・ Al ₂ O ₃ (purity: 99.9%, average particle size: 0.5 μm) was used. Also, SrCO ₃ (purity: 99.5%, average particle size: 0.5 μm) is used as the SrO component, and Y ₂ O ₃ (purity: 99.5%, average particle size: 0.5 μm) is used as the rare earth oxide. I was there.

First, BN powder having a crystallite size shown in Table 3, the above SrCO ₃ and a sintering aid (Y ₂ O ₃ ) were blended into the starting material of the above sialon composition to prepare a sialon composition, boron nitride, A predetermined raw material mixed powder composition shown in Table 3 consisting of SrCO ₃ and a sintering aid was prepared. The addition weight% of the SrO component and the sintering aid in Table 3 is the weight% based on 100 parts by weight of the total amount of the sialon composition and BN.

Next, a sintered body was manufactured by the same method as in Example 1. The density characteristics (relative density), bending test (3-point bending strength at room temperature according to JIS-R1601), and thermal shock resistance and corrosion resistance of the underwater cooling method were evaluated for the obtained sintered body, and the evaluation results are shown. The results are shown in Table 3. In addition, in Table 3
Nos. 1 to 3 are examples of the present invention, and No. 4 is a comparative example in which SrCO ₃ is not mixed.

[0039]

[Table 3]

As is apparent from Table 3 above, it can be understood that the sialon-based composite sintered bodies of Nos. 1 to 3 in the composition range of the present invention exhibit excellent sintered body characteristics. On the contrary,
In Comparative Example No. 4, the SrO component was not blended, so that it had low density, low strength, low thermal shock resistance, and poor corrosion resistance.

Example 4 No. 1 and No. 12 of Example 1
Sintered the composition (see Table 1 above), φ210 / φ170 × 25
A break ring for horizontal continuous casting of t was manufactured. This is placed between the tundish of the horizontal continuous casting machine and the mold, and is made of stainless steel (SUS 304) and high chromium steel (Cr: 16-18 Wt%
Casting of class, oxygen content 60-100ppm) was carried out. The melt loss index of the break ring at that time was measured, and the results are shown in Table 4. Note that the melt loss index of the break ring in Table 4 below is: melt loss index = {break ring melt loss amount (Dmm) ÷ slab length
(m)} × 100, and the smaller this value is, the smaller the amount of erosion is.

[0042]

[Table 4]

As is clear from the results shown in Table 4, the break ring made of the material of the present invention can be cast for a long time,
It can be understood that the amount of melting loss is extremely smaller than that of the comparative product.

[0044]

INDUSTRIAL APPLICABILITY As described in detail above, the present invention particularly uses BN having a crystallite size of 50 to 150 angstroms and CaO.
Or SrO component is characterized in that it is dense, has sufficient strength, and has the effect of obtaining a sialon-based composite sintered body having excellent thermal shock resistance and corrosion resistance to molten metal. . And according to the present invention,
Sialon composite sintered compact suitable for various nozzle members for molten metal that requires severe heat load and corrosion resistance, horizontal continuous casting of steel, protective pipe for temperature measurement, various burner parts, etc. Can be provided.

[Brief description of drawings]

FIG. 1 is a SEM structural diagram (Scanning Electron Micr) of a sialon-based composite sintered body according to an example of the present invention (No. 2 in Table 1).
oscope: A photograph showing the crystal structure by electron microscopy)

FIG. 2 is a SEM structural chart (Sca) of a comparative example (No. 15 in Table 1).
nning Electron Microscope: A photograph showing a crystal structure by an electron microscope).

Claims (2)

[Claims] (1) Si ₃ N ₄ , AlN, Al ₂ O ₃ or Si ₃ N ₄ , AlN,
Sialon composition consisting of Al ₂ O ₃ and SiO ₂ and represented by Si _6-Z Al _Z O _Z N _8-Z (1 ≦ Z ≦ 3) 30 to 70% by weight, (2) Crystallite size 50
〜150 angstrom boron nitride 20 ~ 70wt%, (3) CaO or SrO component 0.1 ~ 10wt%, (4) Y
And at least one oxide of at least one kind of lanthanide-based metallic element, which is 0.1 to 5% by weight, and is a dense and fine BN of 2 μm or less uniformly dispersed in a sialon matrix. body. 2. (1) Si ₃ N ₄ , AlN, Al ₂ O ₃ or Si ₃ N ₄ , AlN,
The above raw material powder mixture, which is composed of Al ₂ O ₃ and SiO ₂ , and produces 30 to 70% by weight of a sialon composition represented by Si _6-Z Al _Z O _Z N _8-Z (1 ≦ Z ≦ 3), ( 2) 20 to 70% by weight of boron nitride having a crystallite size of 50 to 150 Å, (3) 0.1 to 10% by weight as CaO or SrO component, (4) Y and at least one or more of lanthanide-based metal elements. Oxides 0.1 to 5% by weight are uniformly mixed, and this mixture is molded by isostatic pressing, die molding, casting, injection molding, etc., and the molding is heated to a temperature of 1650 to 18
The method for producing a sialon-based composite sintered body according to claim 1, wherein atmospheric pressure sintering or gas pressure sintering is performed at 50 ° C. in an N ₂ or Ar atmosphere.