Silicon nitride-bonded silicon carbide refractories for molten metal immersion

Abstract

To provide a silicon nitride-bonded silicon carbide refractory that can obtain excellent high-temperature properties. [Solution] The silicon carbide refractory is a silicon nitride-bonded silicon carbide refractory in which the ratio of silicon carbide to silicon nitride is 65% to 75% by mass of silicon carbide and 25% to 35% by weight of silicon nitride. The β ratio in silicon nitride is 60% or more, and it contains 0.5% to 1.0% by mass of Al2O3 component consisting of mullite crystals relative to the total of silicon carbide and silicon nitride, the apparent porosity is 22.0% to 25.0%, and metallic silicon is not detected by X-ray diffraction in a thickness region of at least 5 mm from the surface.

Description

Technical Field

[0001] The present invention relates to silicon nitride-bonded silicon carbide refractories, and more particularly to silicon nitride-bonded silicon carbide refractories for molten metal immersion, which are used by being immersed in molten metals such as aluminum, zinc, copper, and lead.

Background Art

[0002] Since silicon nitride-bonded silicon carbide refractories are excellent in corrosion resistance, thermal shock resistance, etc., they have been conventionally used as tools such as linings, immersion tubes, and protection tubes of aluminum melting furnaces. Patent Document 1 discloses an invention of a method for producing a silicon nitride-bonded silicon carbide refractory characterized in that a molded body having a main component of SiC containing at least 5 to 20 wt% of Si and 1 to 10 wt% of β-Si3N4 is fired in an N2 gas atmosphere, the β ratio of Si3N4 in the fired refractory is 55% or more, and the Si remaining in the refractory is substantially 0 wt%. According to the examples of Patent Document 1, the fired silicon nitride-bonded silicon carbide refractories produced by the production method are composed of 89 wt% of SiC, 11 wt% of Si3N4, residual Si = 0%, porosity = 14%, 12% (Examples 1, 3), or 52 wt% of SiC, 48 wt% of Si3N4, residual Si = 0%, porosity = 10%, 13% (Examples 2, 4). According to the invention described in Patent Document 1, it is possible to enhance the thermal shock resistance that could not be obtained with conventional SiC refractories or Si3N4 refractories, realize a refractory having high strength, and significantly reduce the cost as a consumable for aluminum melting furnaces.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the invention described in Patent Document 1, while a wide range of compositions of 50-90% by weight of SiC and 50-10% by weight of Si3N4 are described as the overall concept of the invention, only two cases are shown in the examples: 89% by weight of SiC and 11% by weight of Si3N4, or 52% by weight of SiC and 48% by weight of Si3N4. In the former case, the amount of Si3N4 that enhances bond strength is insufficient, leading to problems such as insufficient high-temperature strength, especially under an oxidizing atmosphere, while in the latter case, problems such as crack formation and increased residual Si occurred. Furthermore, in all of the above examples, the material consisted only of two components, SiC and Si3N4, and the molten metal's resistance to penetration was not sufficient. Additionally, the porosity after firing was low, at 10-14%, leading to problems such as reduced thermal shock resistance.

[0005] This invention is based on these problems and aims to provide a silicon nitride-bonded silicon carbide refractory for molten metal immersion that can obtain excellent high-temperature properties that enable a longer service life. [Means for solving the problem]

[0006] The silicon nitride-bonded silicon carbide refractory for molten metal immersion of the present invention has a silicon carbide to silicon nitride ratio of 65% to 75% by mass of silicon carbide and 25% to 35% by weight of silicon nitride, with a β ratio of 60% or more in silicon nitride, containing 0.5% to 1.0% by mass of Al2O3 components consisting of mullite crystals relative to the total of silicon carbide and silicon nitride, having an apparent porosity of 22.0% to 25.0%, and metallic silicon not detectable by X-ray diffraction in at least a thickness region of 5 mm from the surface. [Effects of the Invention]

[0007] The silicon nitride-bonded silicon carbide refractory for molten metal immersion of the present invention exhibits high high-temperature strength, thermal shock resistance, and resistance to molten metal penetration in an oxidizing atmosphere, resulting in excellent high-temperature properties that enable a longer service life. [Brief explanation of the drawing]

[0008] [Figure 1] This is a diagram illustrating a method for measuring high-temperature bending strength. [Figure 2] This diagram illustrates the method for measuring thermal shock resistance. [Figure 3] This diagram illustrates a method for measuring resistance to molten zinc penetration. [Figure 4] This is an X-ray diffraction pattern showing the detection of metallic silicon in a 5 mm thick region from the surface of the sintered body. [Figure 5] This is an X-ray diffraction pattern showing the detection of mullite crystals in the sintered body of Example 1. [Figure 6] This is an X-ray diffraction pattern showing the detection of mullite crystals in the sintered body of Comparative Example 5. [Modes for carrying out the invention]

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0010] A silicon nitride-bonded silicon carbide refractory according to one embodiment of the present invention is a silicon carbide (SiC) aggregate particle bonded by silicon nitride (Si3N4) and grain boundary bonds containing silicon carbide, wherein the ratio of silicon carbide to silicon nitride is 65% to 75% by mass of silicon carbide and 25% to 35% by weight of silicon nitride, wherein the β ratio in the silicon nitride is 60% or more, and the Al2O3 component consisting of mullite crystals is contained at 0.5% to 1.0% by mass relative to the total of the silicon carbide and silicon nitride, the apparent porosity is 22.0% to 25.0%, and metallic silicon is not detectable by X-ray diffraction in a thickness region of at least 5 mm from the surface.

[0011] The silicon nitride-bonded silicon carbide refractory for molten metal immersion of the present invention has excellent thermal shock resistance, particularly due to its relatively high apparent porosity of 22.0% to 25.0%, and despite this relatively high porosity, the ratio of silicon carbide to silicon nitride is 65% to 75% by mass of silicon carbide and 25% to 35% by weight of silicon nitride, and the β ratio in the silicon nitride is 60% or more, which is beneficial in a highly oxidizing atmosphere. By maintaining high-temperature strength and including 0.5% to 1.0% by mass of Al2O3 components made of mullite crystals relative to the β ratio and the sum of the silicon carbide and silicon nitride, the material exhibits excellent resistance to molten metal penetration. Furthermore, since metallic silicon is not detected by X-ray diffraction in a thickness region of at least 5 mm from the surface, the resistance to molten metal penetration is enhanced, and erosion due to contact with the molten metal is reduced. As a result, it is possible to extend the service life for use in molten metal immersion applications.

[0012] The apparent porosity of the silicon nitride-bonded silicon carbide refractory of the present invention is 22.0% or more and 25.0% or less. If the apparent porosity is less than 22.0%, problems such as a decrease in thermal shock resistance occur, and if it exceeds 25.0%, problems such as a decrease in high-temperature strength occur.

[0013] In the silicon nitride-bonded silicon carbide refractory of the present invention, the ratio of silicon carbide to silicon nitride is 65% to 75% by mass for silicon carbide and 25% to 35% by mass for silicon nitride, and the β ratio in the silicon nitride is 60% or more. This allows the material to maintain high-temperature strength under a highly oxidizing atmosphere while having the apparent porosity. If the silicon carbide content is less than 65% by mass and the silicon nitride content is more than 35% by mass, a large amount of metallic silicon is required during manufacturing, which leads to microcracks due to excessive reaction and results in insufficient strength. Furthermore, if the silicon carbide content is more than 75% by mass and the silicon nitride content is less than 25% by mass, the amount of metallic silicon used during manufacturing is insufficient, leading to problems such as low strength due to insufficient reaction.

[0014] In the silicon nitride-bonded silicon carbide refractory, there is no metallic silicon present in at least the 5 mm thickness region from the surface, and metallic silicon is not detected by X-ray diffraction. As a result, the effect of reducing erosion due to contact with molten metal can be obtained.

[0015] This silicon nitride-bonded silicon carbide refractory can be manufactured, for example, as follows. First, as raw materials, for example, silicon carbide aggregate, silicon carbide fine powder, silicon nitride fine powder, metallic silicon fine powder, mullite (Al6Si2O 13 ) powder, and raw materials of other components such as iron are prepared as needed and weighed. It is preferable that the particle size of the silicon carbide aggregate is 0.3 mm to 3.0 mm, the particle size of the silicon carbide fine powder is 100 μm or less, the particle size of the silicon nitride fine powder is 0.1 μm to 10 μm, the particle size of the metallic silicon fine powder is 50 μm or less, and the particle size of the raw materials of other components is 20 μm or less.

[0016] Next, for example, a solvent such as water, a dispersant, a binder, etc. are added to the raw materials and kneaded. Subsequently, for example, the kneaded material is poured into a mold, in-mold curing is performed for a predetermined time, taken out of the mold, and natural drying and high-temperature drying are performed for a predetermined time. Then, it is fired in a nitrogen gas atmosphere. The firing temperature preferably has a maximum holding temperature of 1430 °C to 1460 °C, and the maximum temperature holding time is preferably 8 hours to 12 hours. By the above firing, the mullite powder becomes a component of Al2O3 composed of mullite crystals, which are alumina-silica compounds, rather than corundum, which is alumina crystals after firing.

[0017] Thus, according to this embodiment, especially due to the relatively high porosity of 22.0% or more and 25.0% or less in apparent porosity, it has excellent thermal shock resistance. Even with this relatively high porosity, it is a silicon nitride-bonded silicon carbide refractory where the ratio of silicon carbide to silicon nitride is 65% by mass or more and 75% by mass or less for silicon carbide, and 25% by mass or more and 35% by mass or less for silicon nitride. The β ratio in the silicon nitride is 60% or more, which maintains high-temperature strength in a high-oxidizing atmosphere. And by containing 0.5% by mass or more and 1.0% by mass or less of the Al2O3 component composed of mullite crystals with respect to the total of the β ratio and silicon carbide and silicon nitride, it has excellent resistance to molten metal infiltration. Furthermore, in at least a 5 mm thickness region from the surface, no silicon metal is detected by X-ray diffraction, which reduces erosion due to contact with molten metal. As a result, it can extend the service life for use in molten metal immersion.

[0018] Therefore, this silicon nitride-bonded silicon carbide refractory is more preferably used as an immersion tube for molten metal immersion, specifically for use in immersion tubes such as heater protection tubes and thermocouple protection tubes, especially when immersed in molten metals such as aluminum, zinc, copper, and lead.

Examples

[0019] (Example 1) First, as raw materials, silicon carbide aggregates with a particle size of 0.3 mm to 3.0 mm, silicon carbide fine powder with a particle size of 100 μm or less, silicon nitride fine powder with a particle size of 0.1 μm to 10 μm, silicon metal fine powder with a particle size of 30 μm or less, and mullite powder with a particle size of 20 μm or less were prepared and weighed. The blending ratios of the silicon carbide aggregates, silicon carbide fine powder, silicon nitride fine powder, and silicon metal fine powder were 50% by mass for the silicon carbide aggregates, 25% by mass for the silicon carbide fine powder, 10% by mass for the silicon nitride fine powder, and 15% by mass for the silicon metal fine powder. The blending ratio of the mullite powder that becomes the Al2O3 component was 2.0% by mass with respect to the total of the silicon carbide aggregates, silicon carbide fine powder, silicon nitride fine powder, and silicon metal fine powder. Also, the β ratio in the silicon nitride fine powder of the raw materials was 65%.

[0020] Next, water, ammonium polycarboxylate as a dispersant, and a water-soluble epoxy resin as a binder were added to the raw materials and mixed to obtain a slurry. The proportions of these were 10% by mass of water, 0.1% by mass of the dispersant, and 1% by mass of the binder, relative to the total of silicon carbide aggregate, silicon carbide fine powder, silicon nitride fine powder, and metallic silicon fine powder. Mixing was carried out for 30 minutes using a 100L Dalton mixer. Furthermore, immediately before molding, 0.1% of an aliphatic polyamine, which is a curing accelerator, was added and mixed again for 10 minutes.

[0021] Next, the slurry was placed in a mold and cast with vibrations of 25 Hz or higher. The mold was a single-ended tube shape with an outer diameter of 200 mm, an inner diameter of 170 mm, and a total length of 1200 mm. After curing in the mold for 24 hours, it was removed from the mold and air-dried for 48 hours, followed by high-temperature drying at 100°C for 48 hours. Then, it was fired in a nitrogen gas atmosphere with a maximum holding temperature of 1450°C and a maximum holding time of 10 hours. This yielded a fired silicon nitride-bonded silicon carbide refractory body.

[0022] (Examples 2, 3 and Comparative Examples 1, 2) Except for changing and adjusting the blending ratio of silicon carbide fine powder and metallic silicon fine powder in the raw materials, the silicon nitride-bonded silicon carbide refractory was manufactured in the same manner as in Example 1. Comparative Example 1 was modified to have a higher proportion of silicon nitride in the silicon nitride-bonded silicon carbide refractory, and Comparative Example 2 was modified to have a higher proportion of silicon carbide in the silicon nitride-bonded silicon carbide refractory.

[0023] (Evaluation method) <Method for determining silicon carbide and silicon nitride in calcined bodies> Samples obtained by pressure molding fine powder from crushed calcined bodies were quantitatively analyzed by X-ray fluorescence. The quantitative analysis method used was the Fundamental Parameter Method (FP). The FP method is a technique that performs quantitative calculations using known parameters and measured X-ray fluorescence intensity. Since the Si in SiC, Si3N4, and metallic silicon is calculated as Total.Si, the content of SiC, Si3N4, and metallic silicon was calculated from the analytical values ​​of N and C, and the abundance ratio of SiC and Si3N4 (the respective ratio to the total of SiC and Si3N4) excluding metallic silicon was calculated. In addition, since Si2ON2 and SiO2 are generated when oxygen is mixed in during nitriding calcination, it was confirmed in advance by powder X-ray diffraction that there were no peaks of Si2ON2 or SiO2.

[0024] <Method for measuring the β ratio of silicon nitride in calcined bodies> The fine powder samples obtained by crushing the calcined body were analyzed using a powder X-ray diffractometer, and the first and second peaks of α-Si3N4 and β-Si3N4 were measured. The following formula was used to calculate the peak height ratio. β ratio = (A + B) / (A + B + C + D) A: First peak of β-Si3N4 B: Second peak of β-Si3N4 C: α-Si3N4 first peak D: α-Si3N4's second peak

[0025] <Mullite crystals Al6Si2O in the calcined body> 13 A method for quantifying the concentration of Al2O3 consisting of the following: Samples obtained by pressure molding a fine powder from a crushed calcined body were quantitatively analyzed by X-ray fluorescence, and the Al component was calculated as the oxide Al2O3. The quantitative analysis method used was the fission product (FP) method. In addition, the emergence of mullite crystal peaks was confirmed by powder X-ray diffraction.

[0026] <Method for measuring the apparent porosity of fired bodies (JIS R 2205)> A sample measuring 20mm x 20mm x 100mm was used, and its dry weight, water weight, and water-saturated weight were measured and calculated using the following formula. Apparent porosity = (water-saturated weight - dry weight) / (water-saturated weight - water-saturated weight) Dry weight: Weight measured after drying the sample at 110°C for 24 hours. Weight underwater: The sample was placed in a boiling bath, boiled for 4 hours, cooled, and then measured by suspension underwater. Water-containing weight: The weight measured after removing the sample from the water and wiping the surface with a damp cloth.

[0027] <Method for detecting metallic silicon in a 5mm thick region on the surface of a sintered body> A fine powder sample, obtained by cutting a 5mm x 5mm x 5mm depth section from the surface of the sintered body and then grinding it, was analyzed using a powder X-ray diffractometer, and the presence or absence of the first peak of metallic silicon was used for confirmation.

[0028] <High-temperature strength under an oxidizing atmosphere> The high-temperature bending strength was measured as follows, based on the method for measuring high-temperature bending strength (JIS-R2656). First, as shown in Figure 1, a sample S measuring 20 mm × 20 mm × 100 mm was used and placed in the furnace supported at both ends by support rolls R with a spacing of 60 mm. Next, the sample S was heated to 1400°C at a heating rate of 100°C per hour and held for 2 hours. Subsequently, using a material testing machine capable of maintaining a constant load rate, a load of 0.25 MPa / s was applied to the center of the sample S, and the maximum load at which the sample S fractured at three points was measured. The three-point bending strength was calculated using the following formula. As a result, a calculated three-point bending strength of 50 MPa was evaluated as ◎, 30 MPa to 50 MPa as ○, and 30 MPa or less as ×. 3-point bending strength (MPa) = 3WL1 / 2bd 2 W: Maximum load (N) L1: Center-to-center distance of support roll R = 60 mm b: Sample S width = 20 mm d: Thickness of sample S = 20 mm

[0029] <Thermal shock resistance (JIS-R2657)> As shown in Figure 2, a sample 11 measuring 230 mm × 114 mm × 65 mm was used and inserted into the furnace 13 so that approximately 1 / 3 (76 mm) of the sample was outside the heating surface 12 measuring 114 mm × 65 mm. After the furnace temperature initially dropped and reached 1200°C, it was maintained at 1200°C for 15 minutes. Then, the sample 11 was removed from the furnace 13, the inserted 1 / 3 was immersed in running water for 3 minutes to cool, and after being removed from the running water, it was air-cooled for 12 minutes to record the crack initiation and elongation of the sample 11. This heating, water cooling, and air cooling process was repeated until the sample 11 peeled off. If the sample 11 did not peel off, the process was repeated 10 times. The furnace temperature was measured using a thermocouple 14 placed near the heating surface 12. As a result, if the peeling did not occur after 10 repetitions, it was evaluated as ◎; if peeling occurred between 6 and 10 repetitions, it was evaluated as ○; and if peeling occurred between 1 and 5 repetitions, it was evaluated as ×.

[0030] <Resistance to molten zinc penetration> As shown in Figure 3(A), metallic zinc 23 was melted in a 10L capacity alumina crucible 22 installed inside the electric furnace 21, and a holder 25 with 4 to 5 Φ20 × 120 mm samples 24 attached was rotated to immerse them evenly. After 500 hours of immersion, the samples 24 were collected, and as shown in an enlarged view in Figure 3(B), the zinc penetration rate was measured by cutting the sample 24 at a predetermined position in the zinc-impregnated portion. In Figure 3(B), the zinc-impregnated portion is given a matte finish, and the cutting position 26 is indicated by a dashed line. The zinc penetration rate was defined as the ratio of the cross-sectional area of ​​the discolored layer impregnated with zinc to the cross-sectional area of ​​the sample 24 (substrate cross-sectional area), and was calculated using the following formula. A zinc penetration rate of 0% was marked with ◎, 5% or less with ○, 10% or less with △, and all rates exceeding 10% with ×. Zinc penetration rate = (Cross-sectional area of ​​substrate - Cross-sectional area of ​​non-discolored area / Cross-sectional area of ​​substrate × 100)

[0031] (Evaluation results) Table 1 shows the evaluation results for Examples 1-3 and Comparative Examples 1 and 2. As shown in Table 1, Examples 1-3 had apparent porosity of 22.0%, 23.6%, and 25.0%, respectively, and good results were obtained for high-temperature strength, thermal shock resistance, and zinc penetration resistance under an oxidizing atmosphere. In contrast, Comparative Example 1, which had a higher proportion of silicon nitride, had an apparent porosity of 21.3%, but fine cracks occurred, resulting in insufficient high-temperature strength under an oxidizing atmosphere. Similarly, Comparative Example 2, which had a higher proportion of silicon carbide, had an apparent porosity of 25.7%, resulting in insufficient high-temperature strength under an oxidizing atmosphere. Furthermore, neither Comparative Example 1 nor Comparative Example 2 achieved sufficient high-temperature strength and thermal shock resistance under an oxidizing atmosphere. The reason for this is presumed to be that in Comparative Example 1, a large amount of metallic silicon was required during manufacturing, leading to microcracks due to excessive hydration reaction and resulting in insufficient strength, while in Comparative Example 2, the low amount of metallic silicon during manufacturing made it more susceptible to strength reduction due to insufficient reaction. In other words, it was found that by setting the ratio of silicon carbide to silicon nitride to 65% to 75% by mass of silicon carbide and 25% to 35% by mass of silicon nitride, and setting the apparent porosity to 22.0% to 25.0%, excellent high-temperature properties can be obtained that exhibit superior high-temperature strength and thermal shock resistance under an oxidizing atmosphere, enabling a longer service life.

[0032] [Table 1]

[0033] (Examples 4, 5 and Comparative Example 3) Except for changing the β ratio of silicon nitride in the silicon nitride-bonded silicon carbide refractory by altering and adjusting the β ratio in the silicon nitride fine powder as a raw material, the silicon nitride-bonded silicon carbide refractory was manufactured in the same manner as in Example 1. Comparative Example 3 was manufactured with a lower β ratio. Examples 4 and 5 and Comparative Example 3 were evaluated in the same manner as in Example 1. The evaluation results, along with the results for Example 1, are shown in Table 2.

[0034] As shown in Table 2, Examples 1, 4, and 5 yielded good results in terms of high-temperature strength, thermal shock resistance, and zinc penetration resistance under an oxidizing atmosphere. In contrast, Comparative Example 3, with its low β ratio, exhibited insufficient thermal shock resistance. This is presumed to be due to the low formation of needle-shaped β silicon nitride crystals in Comparative Example 3, resulting in insufficient brittleness of the structure. In other words, it was found that by setting the β ratio of silicon nitride to 60% or higher, excellent high-temperature properties that enable a longer service life can be obtained.

[0035] [Table 2]

[0036] (Comparative Example 4) Except for changing and adjusting the resting time before molding after slurry preparation so that metallic silicon remained in a 5 mm thickness region from the surface of the silicon nitride-bonded silicon carbide refractory, the silicon nitride-bonded silicon carbide refractory was manufactured in the same manner as in Example 1. Comparative Example 4 was also evaluated in the same manner as in Example 1. The evaluation results are shown in Table 3 along with the results for Example 1, and Figure 4 shows the X-ray diffraction pattern in a 5 mm thickness region from the surface of the sintered body. For reference, the X-ray diffraction pattern of Comparative Example 3 is also shown in Figure 4.

[0037] As shown in Figure 4, the first peak of metallic silicon was not detected in Example 1 and Comparative Example 3, whereas the first peak of metallic silicon was detected in Comparative Example 4. In other words, it was found that metallic silicon remained in a 5 mm thickness region from the surface in Comparative Example 4. Furthermore, as shown in Table 4, while good results were obtained for high-temperature strength, thermal shock resistance, and zinc penetration resistance under an oxidizing atmosphere in Example 1, in Comparative Example 4, the high-temperature strength and zinc penetration resistance under an oxidizing atmosphere were insufficient, and erosion by molten zinc was observed during the evaluation of molten zinc penetration resistance. In other words, it was found that if metallic silicon is not detected in a 5 mm thickness region from the surface, excellent high-temperature properties that enable a longer service life can be obtained.

[0038] [Table 3]

[0039] (Examples 6, 7 and Comparative Examples 5, 6) Except for changing the blending ratio of mullite powder, which constitutes the Al2O3 component, to the total of silicon carbide aggregate, silicon carbide fine powder, and silicon nitride fine powder in the raw materials, the concentration of the Al2O3 component in the silicon nitride-bonded silicon carbide refractory was changed. Otherwise, the silicon nitride-bonded silicon carbide refractory was manufactured in the same manner as in Example 1. Furthermore, in Comparative Example 5, without changing the firing temperature, the Al2O3 component was replaced with corundum, which is alumina crystal, instead of mullite crystal. In other words, Comparative Example 5 did not contain the Al2O3 component consisting of mullite crystals, while Comparative Example 6 had a higher concentration of the Al2O3 component consisting of mullite crystals.

[0040] Examples 6 and 7 and Comparative Examples 5 and 6 were evaluated in the same manner as in Example 1. The evaluation results, along with those for Example 1, are shown in Table 4. Figure 5 shows the X-ray diffraction pattern of the sintered body of Example 1, as well as Examples 1, 6, 7 and Comparative Example 6, and Figure 6 shows the X-ray diffraction pattern of the sintered body of Comparative Example 5. As shown in Figure 5, mullite crystals were confirmed in Example 1, whereas they were not confirmed in Comparative Example 5. In addition, mullite crystals were confirmed in Examples 6 and 7 and Comparative Example 6, similar to Example 1.

[0041] Furthermore, as shown in Table 4, in Examples 1, 6, and 7, good results were obtained in terms of high-temperature strength, thermal shock resistance, and zinc penetration resistance under an oxidizing atmosphere. In contrast, Comparative Example 5, which did not contain the Al2O3 component made of mullite crystals, showed insufficient high-temperature strength and zinc penetration resistance under an oxidizing atmosphere, and Comparative Example 6, which had a high concentration of the Al2O3 component made of mullite crystals, showed insufficient high-temperature strength and thermal shock resistance under an oxidizing atmosphere. In other words, it was found that by setting the Al2O3 component made of mullite crystals to 0.5% by mass or more and 1.0% by mass or less relative to the total of silicon carbide and silicon nitride, excellent high-temperature properties that enable a longer service life can be obtained.

[0042] [Table 4]

[0043] Although the present invention has been described above with reference to embodiments, the present invention is not limited to the above embodiments and can be modified in various ways. For example, although the manufacturing method was specifically described in the above embodiments, the invention is not limited thereto. [Industrial applicability]

[0044] The present invention is particularly useful when used as an immersion tube for metal melting furnaces exceeding 450°C. [Explanation of Symbols]

[0045] S...Sample, R...Support roll, 11...Sample, 12...Heating surface, 13...Furnace, 14...Thermocouple, 21...Electric furnace, 22...Alumina crucible, 23...Metallic zinc, 24...Sample, 25...Holder

Claims

[Claim 1] A silicon nitride-bonded silicon carbide refractory material in which the ratio of silicon carbide to silicon nitride is 65% by mass or more and 75% by mass or less for silicon carbide, and 25% by mass or more and 35% by weight or less for silicon nitride, The β ratio in the silicon nitride is 60% or more. Al made of mullite crystals relative to the sum of the silicon carbide and silicon nitride. ２ O ３ It contains 0.5% by mass or more and 1.0% by mass or less of the component, The apparent porosity is between 22.0% and 25.0%. At least in a 5 mm thickness region from the surface, metallic silicon is not detectable by X-ray diffraction. A silicon nitride-bonded silicon carbide refractory for molten metal immersion, characterized by the following features.

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