JPS642468B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Field of Application) The present invention relates to a tandate nozzle, particularly a nozzle that is most suitable for use in a small cross-section continuous casting method for aluminum killed steel having an aluminum content of 0.010% or more. (Problems to be solved by the prior art and the invention) In continuous casting of aluminum-killed steel, if the aluminum content in the molten steel exceeds 0.010%,
It is well known that deposits mainly composed of α-Al ₂ O ₃ are formed when molten steel passes through commercially available tundish nozzles. There is still no established theory as to the mechanism by which this deposit is formed, but (1) it is a reaction product between the refractory and molten steel, (2) it is molten steel oxide due to air entering through the pores of the refractory, and (3) it is formed in the molten steel due to a decrease in temperature. Adhesion of supersaturated Al ₂ O ₃ precipitates to refractories (4) The cause of this is the adhesion of deoxidation products present in molten steel to refractories. In any case, such deposits cause what is called a nozzle clogging phenomenon, which impedes the supply of molten steel from the tundish nozzle. Particularly in small-section continuous casting, the nozzle diameter cannot be made large, which tends to cause nozzle blockage, and the aluminum content in the molten steel increases.
It is a well-known fact that if it exceeds 0.010%, casting will be seriously hindered. In order to avoid this phenomenon, a method has been proposed in which the deposits on the tundish nozzle are removed using an inert gas, but this method is extremely difficult in small-section continuous casting where the nozzle diameter is small. Furthermore, it is expected that blowing inert gas will disturb the injection flow and easily lead to erosion of the nozzle refractory material, and it is considered that control thereof will be extremely difficult. In addition, the use of a so-called tundish nozzle in which the refractory material is intentionally eroded to a large extent has been devised in order to remove deposits from the tundish nozzle and avoid blockage, but it is impossible to achieve uniform eroding. It is difficult and tends to cause fluctuations in casting speed. In any case, the method of removing deposits from the tandate nozzle has the concern that the deposits may contaminate the molten steel, resulting in an extremely unfavorable quality defect. Another method is to increase the diameter of the tundish nozzle to avoid nozzle blockage, but this requires the use of a stopper or sliding gate valve to appropriately control the molten steel supply rate. Although clogging of the nozzle can be avoided by using such a large-diameter tundish nozzle, fluctuations in the molten steel supply rate due to adhesion and detachment are unavoidable. Particularly in small cross-section continuous casting, this variation causes large variations in the meniscus in the mold, making it extremely difficult to control and causing quality problems. Furthermore, refractory materials such as stoppers and sliding nozzles, or falling off deposits may become a source of contamination of molten steel. (Means and Examples for Solving the Problems) The present invention is concerned with the material and shape of a tandate nozzle that avoids the above-mentioned problems and can easily cast aluminum killed steel even in small cross-section continuous casting. . The present invention will be explained below with reference to FIGS. 1 and 2. FIG. 1 is a sectional view showing a typical example of the nozzle of the present invention, which is a composite nozzle basically composed of a nozzle part 1 and a ring-shaped nozzle part 2. Here, the nozzle part 1 includes a large diameter part 1a forming a flow path 4a for molten steel and a fitting part 4b of a ring-shaped nozzle.
There is a step between the large diameter part on the upstream side and the small diameter part on the downstream side. Therefore, this nozzle part 1 is made of the material of commercially available tundish nozzles, for example, Al ₂ O ₃ -
It is possible to use a material made of SiO ₂ -based ceramics and high alumina refractories, and the diameter D of the large-diameter portion is such that even if deposits mainly composed of α-Al ₂ O ₃ are formed, clogging will occur. You can easily choose any caliber that you think is not available. Next, the ring-shaped nozzle part 2 is a ceramic lining arranged in a ring shape on the inner surface of the end of the small diameter part 1b. In the present invention, this ring-shaped nozzle part is made of ceramics, which is a material that is difficult to wet with molten steel. Non-oxide ceramics are suitable as these materials, and specifically, ZrB 2 , ZrB ₂ ,
ZrB ₂ -BN is preferably composed mainly of one or more of TiC, B ₄ C, AlN, and BN.
ZrB ₂ 95-60% by weight, BN5-40 because the composite is difficult to wet with molten steel and α-Al ₂ O ₃ etc. do not adhere.
% is optimal. A ring nozzle made of such ceramics is preferably an integral sintered ring obtained by sintering an annular ring formed in advance, and is attached to the nozzle body with an appropriate bonding agent. They can be arranged so that they fit together or are intentionally fitted together. As described above, this ring-shaped nozzle part has poor wettability with molten steel, so it is difficult to react with molten steel and is difficult to be damaged by melting by molten steel. Supersaturated Al ₂ O ₃ and deoxidation products in molten steel are less likely to adhere due to temperature drop. It has the following characteristics. Further, the nozzle diameter d of this ring-shaped nozzle portion can be selected from any diameter of 20 mmφ or less, which provides the optimum molten steel supply rate even in small-section continuous casting. Furthermore, although the aforementioned non-oxide ceramics used in this part are generally expensive, the amount used can be greatly reduced by using a composite nozzle like this nozzle, which is used as a ring-shaped nozzle part. It is also extremely advantageous in terms of cost. FIG. 2 is a sectional view showing a typical application example of the present invention, which is composed of a nozzle part 1, a ring-shaped nozzle part 2, and a cylindrical nozzle part 3. The structure of this nozzle is basically the same as the nozzle explained in FIG. 1, and has a large diameter part 1a that forms a flow path 4a for molten steel and a small diameter part 1b that forms a ring-shaped nozzle fitting part 4b. It is something that exists. Here, the ring-shaped nozzle part 2 is at least the end 1 on the upstream side of the molten steel flow of the small diameter part 1b, as in FIG.
c A ceramic lining arranged in a ring shape on the inner surface, and in this example, it is similarly arranged on the inner surface of the end 1d on the downstream side of the molten steel flow. Further, the cylindrical nozzle part 3 is disposed on the inner surface of the small diameter part 1b, preferably at least at the central part in the longitudinal direction, and is located between the ring-shaped nozzle parts 2 disposed at the upstream and downstream ends. These constitute the small diameter portion of the entire tundish nozzle of the present invention. Here, this cylindrical nozzle portion 3 has a straight portion with a length sufficient to rectify the injected flow of molten steel, specifically, a straight pipe portion with a length of at least twice the inner diameter d. Take it as such. The cylindrical nozzle part is desirably made of a finely dense refractory cylindrical body, and preferably has an apparent porosity of 5% or less, as a material suitable for such usage conditions. As a specific material, a sintered body made of quartz, which can have a porosity of almost 0, is most suitable. Similar to the ring-shaped nozzle part of this cylindrical nozzle part, the composite nozzle of the present invention can be obtained by preparing a sintered body in a predetermined shape in advance and disposing it by joining, adhering, fitting, etc. to the nozzle part main body. is easily possible. In this way, this nozzle has a large diameter at the part of the normal material where deposits are likely to form, so the nozzle does not get clogged even if deposits form, and the inlet is located at the small diameter part where the nozzle is most likely to become clogged. The part is made of ceramics that do not easily generate deposits, and in cases where a cylindrical nozzle is installed, a micro-dense material such as quartz that can have a porosity of almost zero is used. It is completely gas-impermeable and the supply of atmospheric oxygen from the outside is cut off, and since it is continuously eroded little by little, it is difficult for precipitates mainly composed of Al ₂ O ₃ to adhere, so it is smooth. An injection flow is obtained. Furthermore, the ring-shaped nozzle made of ceramic, which does not easily get wet, located at the nozzle outlet ensures ideal flow rectification with extremely little expansion of the diameter due to the flow of molten steel. Furthermore, as a result of using the above nozzle, α-
Nozzle blockage due to deposits mainly composed of Al ₂ O ₃ can be avoided, and on the other hand, the nozzle diameter can be arbitrarily selected, eliminating the need for a stopper or sliding gate valve. Moreover, since the length of the cylindrical nozzle portion is sufficient, the injection flow is rectified, which is advantageous in terms of operation and product quality. The effects of using this nozzle will be further explained below with reference to actual measurement data. The molten steel used in the test was aluminum killed steel made in an electric furnace - outside furnace (LF), and aluminum was added to make the crystal grains finer.
The content is 0.010% to 0.035%. For comparison, we also conducted some casting tests using molten steel with a low aluminum content. The above molten steel was cast in a 130 x 130 mm billet continuous caster using various tandate nozzles with an inner diameter of 15 mmφ. Next, we defined the pouring rate index by expressing the amount of molten steel that passed through the tundish nozzle as a ratio to the amount of molten steel in the ladle, and evaluated the effects of various tundish nozzles on nozzle clogging. Figure 3 shows the results. showed that. In other words, a pouring rate index of 1 indicates that the entire amount of molten steel in the ladle has been completely cast without clogging the nozzle. Referring to Figure 3, this shows the relationship between the aluminum content in steel and the pouring rate index for various _tundish nozzles. Nozzle, test was Siamotsu type (Al ₂ O ₃ 40% - SiO ₂ 60%) tandate nozzle,
The test results were obtained using the tundish nozzle according to the invention described in the note below. In other words, the test showed that as the aluminum content in molten steel increased, the pouring rate index decreased rapidly, and when the aluminum content exceeded 0.010%, it became almost impossible to pour due to nozzle blockage, and the test showed that the Although the pouring rate index is large, as the aluminum content in the molten steel increases, the pouring speed decreases due to deposits on the tandate nozzle, and when the aluminum content exceeds 0.010%, the clogging phenomenon becomes noticeable and the process is completed. This indicates that it can no longer be cast. On the other hand, tests showed that the aluminum content in molten steel was
Even if it exceeded 0.030%, almost complete casting was possible and casting was stable. In addition, according to findings after casting this nozzle, deposits were observed on the outer nozzle part, which is made of normal material, but due to the large diameter, the nozzle did not become clogged, and the ring-shaped nozzle part. No deposits were observed on the cylindrical nozzle portion, or if there was any deposits, the amount was small, and the diameter of the nozzle was hardly enlarged due to erosion. Furthermore, other non-oxide ceramics such as TiC, BN, B ₄ C, AlN,
A molten steel casting test was conducted using ZrB _dual- quality ceramics in the same configuration as the test, and the effect on nozzle clogging was investigated. The results are also shown in Figure 3. In addition, the material properties of each ceramic used are shown in the table in the notes. In ZrB _quality ceramics and BN quality ceramics,
Even when the Al content exceeded 0.030%, casting results comparable to those of the ZrB ₂ -BN composite were obtained, and no deposits were observed in the ring-like nozzle and cylindrical nozzle parts. Next, in B ₄ C, TiC, and AlN ceramics,
When the Al content exceeded 0.010%, the pouring rate index tended to decrease slightly, and some deposits were also observed in the ring-shaped nozzle and cylindrical nozzle, but this is shown as a comparative example. Compared to tests using conventional nozzles, significantly more stable casting results were obtained. As shown in the above examples, it has been confirmed that the nozzle of the present invention can stably cast aluminum-killed steel having an aluminum content of 0.010% or more in molten steel even in continuous casting of small cross-section billets. (Note) ◎Nozzle size 〇Nozzle body; Inner diameter D70mm, Length 130mm 〇Ring nozzle part; Inner diameter d15mm (both upper and lower ends) Outer diameter 29mm, Thickness 5mm 〇Cylindrical nozzle part; Inner diameter 15mm, Outer diameter 29mm, Length 50mm ◎Material properties of the nozzle 〇Nozzle body Shamotsu properties: Softening point under load 2Kg/T ₂ (℃) 1450℃ Hot compressive strength 400Kg/cm ² at 1260℃ Bending strength 80Kg/cm ² Coefficient of thermal expansion at 1000℃ 0.45% 〇Ring-shaped nozzle part

【table】

[Table] 〇Cylindrical nozzle part Composition SiO ₂ ; 99.99% or more Physical properties Maximum operating temperature 1500℃ Bending strength 350Kg/cm ² or more Hardness (Mohs) 6 Coefficient of thermal expansion 5 × 10 ^-7 Porosity 0.2% 〇 Manufacturing method of composite nozzle Each nozzle...nozzle body, ring nozzle,
Make individual cylindrical nozzles. These are fitted and integrated with adhesive as shown in Figure 2. The above results were obtained with a nozzle based on the configuration shown in Figure 2, but when a nozzle based on the configuration shown in Figure 1 was manufactured in the same way and used in the same way, almost the same effect was confirmed. did. This shows that the structure based on FIG. 1 is more advantageous depending on the usage conditions, considering that it has a simpler configuration. (Effects of the invention) By using the nozzle of the present invention, it is possible to avoid clogging of the nozzle due to deposits mainly composed of 1 α-Al ₂ O ₃ , and at the same time, the nozzle diameter can be arbitrarily selected, so it is possible to avoid stoppers and sliding. Gate valve is not required. 2. The diameter d of the small-diameter nozzle part can be selected from any diameter of 20 mmφ or less that provides the optimum molten steel supply rate in small-section continuous casting. 3. Furthermore, other non-oxide ceramics such as the above-mentioned ZrB ₂ -BN suitable for forming the small-diameter nozzle part are generally expensive, but they are suitable for forming a composite nozzle used as a ring-shaped nozzle part like the nozzle of the present invention. By doing so, the amount used can be significantly reduced, which is extremely advantageous in terms of cost. It has various effects such as, and has great practical value.

[Brief explanation of drawings]

FIGS. 1 and 2 are cross-sectional views showing embodiments of the nozzle of the present invention, and FIG. 3 is an explanatory diagram showing the relationship between the amount of aluminum in molten steel and the pouring amount index when various nozzles are used. In the drawings, 1 is a nozzle main body, 2 is a ring-shaped nozzle part, 1a is a large diameter part of the nozzle, and 1b is a small diameter part 3 is a cylindrical nozzle part.

Claims (1)

[Claims] 1. A nozzle for forming a flow path for molten steel, which has a large diameter part on the upstream side and a small diameter part on the downstream side, and there is a step between the large diameter part and the small diameter part. TiC, BN, B ₄ C, on the inner surface of at least the upstream end of the bore.
A nozzle for casting molten steel characterized by having a ring-shaped ceramic lining containing at least one of AlN and _ZrB2 as a main component. 2 Also on the inner surface of the downstream end of the molten steel flow in the small diameter section.
2. The nozzle according to claim 1, comprising a ring-shaped ceramic lining containing at least one of TiC, BN, B ₄ C, AlN, and ZrB ₂ as a main component. 3. The nozzle according to claim 1 or 2, wherein at least the inner surface of the central portion in the longitudinal direction of the small diameter portion is formed of a ceramic cylindrical body with a porosity of 5% or less. 4. The nozzle according to claim 3, wherein the ceramic cylindrical body is made of quartz. 5. Any one of claims 1 to 4 in which a previously integrally molded and sintered annular ring whose main component is one or more of TiC, BN, B ₄ C, AlN, and ZrB ₂ is used as the inner lining. or the nozzle described in one of the above. 6. The nozzle according to any one of claims 1 to 5, wherein the diameter d of the small diameter portion is 20 mm or less. 7. The nozzle according to any one of claims 1 to 6, which is used for casting aluminum killed steel.