JP2007130653A - Immersion nozzle for continuous casting - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an immersion nozzle for continuous casting, which fully exerts the performance of a hard-to-adhere refractory arranged in the inner periphery of the immersion nozzle so that the deposition of precipitates does not occur even at the front ends of discharge holes and a slit. <P>SOLUTION: In the immersion nozzle for continuous casting, a magnesia-lime based refractory 22 of a cylindrical inner periphery is integrally formed with a zirconia-lime-graphite or zirconia-graphite refractory 24 of a cylindrical outer periphery. The cylindrical inner periphery is formed of the magnesia-lime based refractory 22, including front ends 9 of discharge-holes and a slit. The cylindrical outer periphery is formed of the zirconia-lime-graphite or zirconia-graphite refractory 24. The inner surfaces of discharge holes 2 and a slit 3 are covered with the magnesia-lime based refractory, including the front ends 9, so that the deposition of precipitates is prevented. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an immersion nozzle for injecting molten metal from a tundish into a mold in continuous casting of molten metal.

  In continuous casting of molten metal, molten metal is poured from a ladle into a tundish, and further poured into the mold from the tundish. In the mold, a solidified shell grows at the contact portion between the molten metal and the mold, and the solidified shell further pulls downward to further solidify. Finally, solidification is completed and a cast piece is drawn out.

  In continuous casting of slabs and large-section blooms, a continuous casting nozzle called an immersion nozzle is provided below the tundish inlet, and the molten metal discharge hole at the tip of the immersion nozzle is immersed in the molten metal in the mold. By injecting, the injected molten metal can be injected into the mold without being brought into contact with the oxidizing atmosphere.

  As a molten metal outflow path from the tip of the immersion nozzle, two discharge holes 2 directed in the short side direction of the mold are provided near the tip of the bottomed cylindrical immersion nozzle 1, and the molten metal is discharged from the discharge holes 2. The shape is the most common (see FIG. 5). The melt flow rate flowing out from the discharge hole is large, and this melt flow collides with the solidified shell located on the side wall of the mold and is divided into an upflow and a downflow. If the flow velocity of the downward flow is too high, the downward flow penetrates deeply into the molten metal, and inclusions and argon bubbles associated with the downward flow cannot be lifted and caught by the solidified shell, resulting in slab inclusion defects and bubble defects. become. On the other hand, when the flow rate of the upward flow is too large, the upward flow becomes a meniscus reversal flow at the meniscus in the mold. When a stirring flow is caused in the molten metal in the mold by electromagnetic stirring in the mold, a sufficient stirring flow cannot be obtained at the collision portion between the stirring flow and the meniscus reversal flow.

  A nozzle having a slit 3 that opens to the outside downward is known at the bottom of the immersion nozzle 1 (for example, Patent Document 1) (see FIG. 6). The slit 3 is opened by connecting the cylindrical bottom portion 4 and the bottom portions 6 of the left and right ejection holes 2. Since the molten metal flowing into the mold through the immersion nozzle also flows out of the slits in addition to the left and right discharge holes, the flow velocity of the molten metal flowing out of the discharge holes can be relatively reduced, and the discharge flow collides with the solidified shell. Thus, the flow velocity of the downward flow and the upward flow formed is also reduced. As a result of the reduction of the flow velocity of the downward flow, inclusions and argon bubbles that penetrate deeply into the molten metal along with the downward flow can be reduced. As a result of the reduction in the flow velocity of the upward flow, it is possible to reduce the quality defect caused by the fluctuation of the molten metal in the molten metal meniscus in the mold, and to reduce the adverse effect on the stirring flow due to the electromagnetic stirring in the mold. In this way, the immersion nozzle having two discharge holes and slits is hereinafter also referred to as “dispersion nozzle”.

  As the material of the immersion nozzle, fused quartz or alumina graphite refractory is used. Alumina-graphite refractory nozzles are characterized by a combination of high refractory resistance of alumina and low steel wettability with low C, strong corrosion resistance against molten steel, and excellent corrosion resistance compared to fused quartz nozzles. Is the most widely used immersion nozzle for continuous casting of molten steel.

The immersion nozzle made of alumina graphite refractory has the property that precipitates are likely to adhere to the molten metal flow portion in the inner peripheral portion of the nozzle through which the molten metal flows. Deposits are often deposited on portions where the temperature gradient of the nozzle inner wall of the non-immersed portion is large and where the molten metal flow velocity is reduced near the discharge holes, which may make casting difficult. Moreover, it is necessary to perform the operation | work which removes a deposit | attachment during casting, and the deposit | attachment removed here is taken in in a slab, becomes a large inclusion, and causes a deterioration of slab quality. The main component of the deposited deposit is αAl ₂ O ₃ , and it is considered that Al ₂ O ₃ contained in the molten metal as a deoxidation product is deposited and deposited on the inner wall of the nozzle. Deposits on the inner wall of the immersion nozzle are particularly observed in continuous casting of aluminum killed steel.

  Patent Document 2 discloses a nozzle in which at least part of the inside of the nozzle is made of doloma / graphite as a continuous casting nozzle. The doloma is also commercially available as a refractory and is made by roasting dolomite, and preferably contains at least 56.5% CaO and 41.5% MgO. The It is contained in the refractory called a magnesia lime refractory in this specification. Using nozzles made of such materials, the doloma creates soluble reaction products that do not clog the nozzles, thereby avoiding clogging problems such as those found in alumina graphite refractory nozzles.

  When adopting the above doloma / graphitic refractory, the inner peripheral surface of the nozzle that comes into contact with the molten metal to be injected is made of doloma / graphitic refractory and is made of a less expensive material as the outer material that does not contact the molten metal to be injected. Things can be used. Even if the conventionally used alumina graphite refractory is used as the outer material, the problem of nozzle clogging does not occur.

  In Patent Document 3, when a magnesia lime refractory is used on the inner peripheral surface of a continuous casting nozzle to prevent deposits from adhering to the inner peripheral surface of the nozzle, An invention that can prevent melting damage at the joint surface and extend the life of the refractory is described. Thereby, it is possible to sufficiently use the magnesia lime refractory even in the continuous casting of ordinary steel, and it is possible to realize casting without nozzle clogging.

JP 2001-205396 A Japanese National Patent Publication No. 11-506393 JP 2004-50288 A

  As described in Patent Documents 2 and 3, when a magnesia lime refractory is used for the inner peripheral portion of the immersion nozzle and an alumina graphite refractory is used for the outer peripheral portion, two points need to be noted. First, when the magnesia lime refractory and the alumina graphite refractory are in direct contact, CaO in the magnesia lime refractory reacts with the alumina graphite refractory to form a low melting point compound, and the refractory in the contact portion. Has a problem of melting. Secondly, since the magnesia lime refractory has a higher coefficient of thermal expansion than alumina graphite refractory, when both the inner peripheral side and the outer peripheral side refractories are in close contact with each other, There is a problem that tensile thermal stress is generated in the alumina graphite refractory on the outer peripheral side and the refractory is damaged.

  In order to deal with the above two problems, conventionally, as shown in FIGS. 5 and 6, the magnesia lime refractory 22 on the inner peripheral side and the alumina graphite refractory 27 on the outer peripheral side are separately molded, and the refractory on the outer peripheral side is formed. The inner diameter of the product is made slightly larger than the outer diameter of the inner refractory, and after molding both refractories, the inner refractory is inserted into the outer refractory and the joint refractory is inserted into the gap between the two refractories. A method of filling the product 29 was adopted. If a magnesia-based material is used as the joint refractory 29, a low melting point compound is not formed even when it comes into contact with the magnesia-lime refractory 22. Also, by ensuring the porosity of the joint refractory 29, the joint refractory 29 contracts when the inner peripheral refractory expands more than the outer peripheral refractory during high-temperature heating, thereby suppressing the generation of thermal stress. Can do.

As described above, when trying to insert the inner refractory into the outer refractory, it is necessary to make the maximum outer diameter of the inner refractory smaller than the inner diameter of the outer refractory. As a result, the alumina graphite refractory 27 is inevitably exposed on the inner surface of the discharge hole 2 in the vicinity of the tip 9 where the discharge hole 2 opens to the outer periphery of the immersion nozzle (FIG. 5). In the immersion nozzle having the slit 3 together with the discharge hole 2, the alumina graphite refractory 27 is also exposed on the slit wall surface near the tip 9 where the slit 3 opens on the outer periphery of the immersion nozzle (FIG. 6). When the alumina graphite refractory 27 is exposed in this way, Al ₂ O ₃ deposited from the molten metal is deposited on that portion, and the molten metal flow path is narrowed or closed, so that it hardly adheres to the inner periphery of the immersion nozzle. The effect using the magnesia lime refractory 22 is not sufficiently obtained.

  The present invention provides an immersion nozzle for continuous casting that sufficiently exhibits the effect of a hardly adherent refractory disposed on the inner peripheral portion of the immersion nozzle and does not cause deposits to deposit at the tip of the discharge hole or slit. The purpose is to do.

That is, the gist of the present invention is as follows.
(1) It has a bottomed cylindrical shape, and two discharge holes 2 are arranged at positions symmetrical to the cylinder in the lower part of the cylindrical side wall, and at least a cylindrical inner peripheral portion of the region including the discharge holes 2 is a discharge hole. The portion including the tip 9 is formed of a magnesia lime refractory 22 and at least a portion of the outer periphery of the cylinder including the discharge hole and excluding the vicinity 10 of the discharge hole is a zirconia lime graphite refractory or a zirconia graphite refractory 24. An immersion nozzle for continuous casting, characterized in that it is formed integrally between a magnesia lime refractory 22 in the inner periphery of the cylinder and a zirconia lime graphite refractory or zirconia refractory 24 in the outer periphery of the cylinder. .
(2) It has a bottomed cylindrical shape, and two discharge holes 2 are arranged in a cylindrically symmetrical position at the bottom of the cylindrical side wall, and the cylinder bottom 4 and the bottoms 6 of both discharge holes are connected to the outside. An opening slit 3 is provided, and at least the inner periphery of the cylinder including the discharge hole 2 is formed of a magnesia lime refractory 22 including the discharge hole tip 9 and the slit tip 9, and includes at least the discharge hole 2. A portion of the outer peripheral portion of the cylinder excluding the vicinity 10 of the discharge hole 2 and the slit 3 is formed of zirconia lime graphite refractory or zirconia graphite refractory 24, and the magnesia lime refractory 22 on the inner periphery of the cylinder and the outer periphery of the cylinder. An immersion nozzle for continuous casting, wherein the zirconia lime graphite refractory or the zirconia graphite refractory 24 is integrally molded.
(3) The immersion nozzle for continuous casting according to (1) or (2) above, wherein the thickness of the magnesia lime refractory 22 on the inner periphery of the cylinder is 7 mm or less.
(4) The upper part of the immersion nozzle has a magnesia lime refractory sleeve 28 at the inner circumference of the cylinder, an alumina graphite refractory 27 at the outer circumference of the cylinder, and a magnesia lime refractory sleeve 28 at the inner circumference of the cylinder. The immersion nozzle for continuous casting according to any one of the above (1) to (3), wherein a sleeve is inserted into the alumina graphite refractory 27 on the outer periphery of the cylinder.

In the present invention, a cylindrical outer peripheral portion of an immersion nozzle is formed of a zirconia lime graphite refractory or a zirconia graphite refractory, and a magnesia lime refractory in a cylindrical inner peripheral portion and a zirconia lime graphite refractory or zirconia graphite refractory in a cylindrical outer peripheral portion. The cylindrical inner periphery can be formed of a magnesia lime refractory including the discharge hole tip and the slit tip. As a result, it was possible to prevent the phenomenon of depositing Al ₂ O ₃ precipitates at the discharge hole and the tip of the slit.

  In the drawings attached with this specification, the irregular dot hatched portion is the portion where the MC refractory is exposed, and the portion where the irregular dot hatching and the hatched hatching overlap shows the cross section of the MC refractory. Further, a portion without hatching is a portion where a refractory other than the MC-based refractory is exposed, and a portion with only hatching indicates a cross section of a refractory other than the MC-based refractory.

  In the present invention, the magnesia lime refractory (hereinafter also referred to as “MC refractory”) is a refractory containing CaO, MgO, more preferably C, and its composition is 0.03. ≦ MgO / CaO ≦ 32, 0.05 ≦ C / (CaO + MgO + C) ≦ 0.40, and the total of CaO + MgO + C is preferably 90% by mass or more.

The crystal structure of the magnesia lime refractory is a mixture of CaO phase and MgO phase, and C is present in the form of a plate-like filling between the grains of CaO and MgO coexisting. Why deposition is less of Al ₂ O ₃ precipitates with the material of the inner peripheral surface nozzle magnesia lime refractories, when the Al ₂ O ₃ deposited from molten metal adhering to the inner peripheral surface nozzle, refractories This is thought to be because the CaO phase and the deposited Al ₂ O ₃ react to form a low melting point material, and the deposited deposits float again in the molten metal. Therefore, if the CaO phase is present in the refractory that forms the inner peripheral surface of the nozzle, it has the ability to prevent deposits from adhering. When the MgO / CaO in the magnesia lime refractory is 32 or less, the CaO phase can be surely present in the refractory, and the effect of preventing deposit adhesion can be exhibited. The lower the MgO / CaO ratio, the greater the abundance ratio of the CaO phase, thereby improving the deposit adhesion preventing effect. It is more preferable that MgO / CaO ≦ 1. It is more preferable that MgO / CaO ≦ 0.72.

The MgO phase in the magnesia lime refractory has a function of suppressing melting damage of the inner surface refractory in order to produce a reaction product having a relatively high melting point with Al ₂ O ₃ in the molten metal. In order to exert this function, it is necessary to satisfy MgO / CaO ≧ 0.03. It is more preferable that MgO / CaO ≧ 0.2. It is more preferable that MgO / CaO ≧ 0.42.

In producing a magnesia lime refractory, dolomite is usually used as a source of CaO-MgO in the refractory. Since the ratio of CaCO ₃ and MgCO ₃ in dolomite varies depending on the production area, the MgO / CaO ratio in the refractory produced using dolomite is in the range of 0.49 to 1. If it is this range, the said preferable MgO / CaO ratio is realizable.

  When C is contained in the magnesia lime refractory, it has a function of being excellent in heat-resistant spalling due to the high thermal conductivity of C. In order to exhibit this function, C / (CaO + MgO + C) needs to be 0.05 or more. More preferably, it is 0.15 or more. However, if the C content is too high, wear due to oxidation of C increases, so C / (CaO + MgO + C) ≦ 0.40. More preferably, C / (CaO + MgO + C) ≦ 0.35.

  In the magnesia lime refractory, the total of CaO + MgO + C is 90 mass% or more. When the impurity content exceeds 10%, the fire resistance is lowered, and it becomes easy to form a low-melting-point substance with the main substance of the refractory material, so that the characteristics as the inner pore body of the present invention cannot be obtained. .

In the present invention, the zirconia lime graphite refractory (hereinafter also referred to as “ZCG refractory”) is a CaO-containing refractory having an Al ₂ O ₃ adhesion preventing ability, and zirconia lime clinker is used as an aggregate, and its spall resistance. Is made of graphite.

  In the present invention, zirconia graphite refractory (hereinafter also referred to as “ZG refractory”) is a material in which zirconia that is chemically stable and has a high melting point is used as an aggregate, and its spall resistance is supplemented with graphite.

In the present invention, alumina graphite refractory (hereinafter also referred to as “AG refractory”) has a melting point lower than that of MgO or ZrO ₂ , but chemically stable alumina is used as an aggregate, and its spall resistance is reduced to graphite. The material supplemented with.

The content of Al ₂ O ₃ in the alumina graphite (AG) refractory is about 60 to 80% by mass. Conventionally, when a magnesia lime (MC) refractory and an AG refractory are brought into contact with each other, the contact portion is melted mainly because the Al ₂ O ₃ component contained in the AG refractory is contained in the MC refractory. This is because it reacts with CaO to produce a low melting point material. In contrast, zirconia lime graphite (ZCG) refractories and zirconia graphite (ZG) refractories have a low content of Al ₂ O ₃ components, and as a result, ZCG refractories and ZG refractories are brought into contact with MC refractories. However, the contact portion does not melt.

  Moreover, when comparing the thermal expansion coefficient at 1000 ° C. for each refractory type, the AG refractory is 0.2%, whereas the MC refractory has a large thermal expansion coefficient of 0.6%, The difference in thermal expansion coefficient between the two was large. When integrally molded with the outer periphery AG refractory and the inner periphery MC refractory, the expansion amount of the inner periphery MC refractory is larger than the expansion amount of the outer periphery AG refractory during high-temperature heating, which causes the outer periphery AG refractory to crack. It had the problem of being easy. On the other hand, the ZCG refractory has a coefficient of thermal expansion of 0.4%, and the ZG refractory has a coefficient of thermal expansion of 0.4%. Therefore, even if both are integrally formed using ZCG refractories or ZG refractories on the outer periphery and MC refractories on the inner periphery, it is possible to reduce the occurrence of cracks due to thermal stress during high-temperature heating.

  The present invention is based on the above knowledge, and in the bottomed cylindrical immersion nozzle, as shown in FIGS. 2 and 3, the inner peripheral part of the cylinder is MC-based refractory 22 and the outer peripheral part of the cylinder is ZCG refractory or ZG refractory 24. Then, the MC refractory 22 on the inner periphery of the cylinder and the ZCG refractory or ZG refractory 24 on the outer periphery of the cylinder are integrally formed. Taking advantage of the integral molding rather than the sleeve insertion, the MC refractory 22 including the discharge hole tip 9 is formed. The discharge hole tip 9 means a tip portion that opens to the outer periphery of the immersion nozzle in the inner wall forming the discharge hole 2. In the immersion nozzle (FIG. 3) having the slit 3, the MC nozzle refractory 22 including the slit tip 9 is formed. The region where the MC-based refractory 22 on the inner periphery of the cylinder and the ZCG refractory or ZG refractory 24 on the outer periphery of the cylinder are integrally formed does not have to be the entire length of the immersion nozzle 1 and includes at least the discharge hole 2. Any area is acceptable. Further, most of the outer periphery of the cylinder in the region including the discharge hole 2 is formed of ZCG refractory or ZG refractory, but in the vicinity 10 of the discharge hole 2 (if the slit 3 is provided, the discharge hole 2 and the slit 3 In the very vicinity 10), the MC-based refractory 22 on the inner peripheral side is exposed, and the outside thereof is formed by the MC-based refractory 24 (see FIGS. 2D and 3D).

  Even if the thermal expansion coefficient of the ZCG refractory or the ZG refractory 24 is large, the thermal expansion coefficient of the MC refractory 22 is still small. Therefore, the thermal stress at the time of high temperature heating still exists for the immersion nozzle in which the inner peripheral portion is the MC-based refractory 22 and the outer peripheral portion is the ZCG refractory or ZG refractory 24 and both are integrally formed. In the present invention, by reducing the thickness of the MC-based refractory 22 at the inner periphery of the cylinder to 7 mm or less, the ZCG refractory and the ZG refractory 24 are forced to expand by expansion of the MC-based refractory 22. As a result, it is possible to reduce the possibility that the refractory is damaged by reducing the thermal stress.

  The thickness of the MC-based refractory 22 is set to 7 mm or less. If the thickness is 7 mm or less, the thermal stress applied to the refractory on the outer peripheral side can be sufficiently reduced. This is because even if the inner peripheral side refractory is worn, it is sufficient as a margin for wear, and the life of the immersion nozzle can be secured.

  Since the ZCG refractory and the ZG refractory 24 are expensive, if the outer peripheral portion of the immersion nozzle is made the ZCG refractory or ZG refractory 24, the cost is excessively increased. In the present invention, as shown in FIG. 1, the upper portion of the immersion nozzle 1 has a cylindrical inner peripheral portion that is a magnesia lime refractory sleeve 28, a cylindrical outer peripheral portion that is an alumina graphite refractory 27, and a cylindrical inner peripheral portion. The magnesia lime refractory sleeve 28 is preferably inserted into the alumina graphite refractory 27 on the outer periphery of the cylinder. Since the sleeve is inserted, the joint refractory 29 can be filled between the outer peripheral refractory and the inner peripheral refractory. Thereby, the outer periphery AG refractory 27 and the inner peripheral MC refractory sleeve 28 are not brought into contact with each other, so that the refractory can be prevented from being melted, and the joint refractory 29 is contracted to heat the refractory 29 at a high temperature. It is possible to prevent occurrence of thermal stress at the time. Therefore, the outer peripheral portion of the upper portion of the immersion nozzle can be an AG refractory 27 with a low cost, and the entire length of the inner peripheral portion can be a hard-to-adhere MC-based refractory sleeve 28.

  In the immersion nozzle 1 shown in FIG. 1, a zirconia lime graphite refractory 25 is used as the outer peripheral refractory in the region including the discharge holes 2, and a zirconia graphite refractory 26 is used as the outer peripheral refractory in the powder line portion of the immersion nozzle 1. Used. By selecting the material in this way, it can be manufactured at the lowest cost while satisfying the function of the refractory of the present invention.

  When manufacturing the above immersion nozzle, the magnesia lime refractory 22 on the inner peripheral side, the zirconia lime graphite refractory 25 on the outer peripheral side, the zirconia graphite refractory 26 and the alumina graphite refractory 27 are integrally formed, and then from above the immersion nozzle. A magnesia lime refractory sleeve 28 is inserted, and a joint refractory 29 is filled between the magnesia lime refractory 28 and the alumina graphite refractory 27.

  In the immersion nozzle having two discharge holes and slits, the molten metal flowing out from the immersion nozzle has a uniform melt flow in any direction from the lower side of the immersion nozzle to the discharge hole opening direction. It is desirable to do. This is because if the molten metal flow is directed only in a specific direction, the flow velocity in that direction is increased, and the flow toward the deep part of the molten metal and the discharge flow from the discharge holes are increased. In addition, when a sliding nozzle is used for the purpose of adjusting the flow rate of molten metal from the tundish through the immersion nozzle, if the sliding nozzle opening area is reduced in order to reduce the molten metal flow rate, the opening portion may be displaced from the central axis of the immersion nozzle. Become. When the conventional dispersion nozzle is used, when the opening portion of the sliding nozzle is deviated from the central axis of the immersion nozzle, the direction of the molten metal flow from the discharge hole may deviate from the discharge hole opening direction.

  In the immersion nozzle of the present invention having two discharge holes 2 and slits 3, as shown in FIG. 4, the portion of the cylindrical bottom 4 that contacts the slit 3 and the portion of the discharge hole bottom 6 that contacts the slit 3 are inclined upward. Therefore, it is preferable that the shape has substantially no step between the surface formed by the cylindrical bottom portion 4 and the surface formed by the discharge hole bottom portion 6. By adopting such a shape, the downward flow and the discharge flow in the mold can be made continuous, and the discharge flow from the discharge holes does not shift even when a sliding nozzle is used.

  If a non-smooth corner exists in the liquid flow path in the submerged nozzle, separation may occur in the liquid flow at the corner, resulting in a negative pressure. As a non-smooth corner of the liquid channel in the immersion nozzle shown in FIG. 3, there is a portion in contact with the cylindrical side wall 5 at the discharge hole top 8. When the immersion nozzle having such a shape is used, when the flow near the meniscus in the mold is disturbed and the molten powder sinks to the vicinity of the discharge hole 2, powder suction is generated in which the molten powder is sucked into the discharge hole 2. There are things to do. The molten powder sucked into the discharge hole 2 is trapped in a deep portion of the slab along with the discharge flow and is likely to become a slab internal defect.

  In the present invention, in the immersion nozzle having two discharge holes 2 and slits 3, as shown in FIG. 4 (a), the portion in contact with the cylindrical side wall at the top of the discharge hole is a curved surface smoothly in contact with the cylindrical side wall. 11 is preferably formed. As a result, the separation caused by the discharge flow at the top of the discharge hole is reduced, thereby eliminating the phenomenon that the molten powder is sucked into the discharge hole.

  Continuous casting of steel was performed with a 2-strand vertical bending slab continuous casting machine using the immersion nozzles of the present invention and comparative examples. The slab thickness is 240 mm, the slab width is 1900 mm, and the ladle capacity is 300 tons. The casting type was low-carbon Al killed steel, the number of continuous castings (the number of heats cast using the same tundish) was 5, and the casting speed was 1.5 m / min.

  The immersion nozzle shown in FIG. 4 was used as an example of the present invention. MC-based refractories 22 are used for all portions in contact with the molten metal flow up to the cylindrical side wall 5, the slit 3 and the tip of the discharge hole 2. On the outer periphery of the immersion nozzle, ZG was used for the powder line, ZCG was used for the discharge hole side from the bower line, and AG refractory was used for the other parts.

  As a comparative example, an immersion nozzle shown in FIG. 7 was used. The outer periphery of the immersion nozzle is an AG refractory 27, and an MC-based refractory 22 is inserted in a sleeve shape therein, and a joint refractory 29 is disposed between the AG refractory 27 and the MC-based refractory 22. Yes. An AG refractory 27 is exposed near the tip of the discharge hole 2.

  Casting was performed by attaching the immersion nozzle of the present invention example to one strand of the continuous casting machine and attaching the immersion nozzle of the comparative example to the other strand.

  About the immersion nozzle of the comparative example, the opening degree of the tundish sliding nozzle started to increase from the middle stage of the fourth heat, and showed signs that the immersion nozzle started. When the immersion nozzle after use was investigated, inclusions adhered to the periphery of the discharge hole, and a clogging tendency was confirmed. On the other hand, the melting loss near the slit was remarkable, and the slit width was about 1.5 times the initial width. This is considered to be a result of the distribution of the discharge flow being biased toward the slit due to the blockage of the discharge holes. In such a shape, it has been confirmed from the results of the water model test that the immersion depth of inclusions due to the downflow of molten steel is increased by about 1.4 times compared to the nozzle of a healthy shape. There is concern about the deterioration of cleanliness.

  About the immersion nozzle of the example of the present invention, the tundish sliding nozzle opening degree and other casting conditions remained stable through 5 heats of casting continuously. After use, it was confirmed that the average material of the inner surface of the submerged nozzle was melted by about 3 mm, but the melting of each part was almost uniform, and the balance of the opening area was maintained even after both the discharge hole and slit were melted. It had been. Therefore, it is considered that the target flow was maintained until the end of casting.

It is a figure which shows the immersion nozzle of this invention, (a) is an AA arrow directional cross-sectional whole figure, (b) is a BB arrow directional cross-sectional partial figure, (c) is CC arrow directional cross-sectional view, d) It is an AA arrow cross-section partial perspective view. It is a fragmentary figure which shows the immersion nozzle of this invention, (a) is AA arrow sectional drawing, (b) is BB arrow sectional drawing, (c) is CC arrow sectional drawing, (d) ) Is a DD arrow view. It is a fragmentary figure which shows the immersion nozzle of this invention, (a) is AA arrow sectional drawing, (b) is BB arrow sectional drawing, (c) is CC arrow sectional drawing, (d) ) Is a cross-sectional perspective view taken along arrow AA. It is a fragmentary figure which shows the immersion nozzle of this invention, (a) is AA arrow sectional drawing, (b) is BB arrow sectional drawing, (c) is CC arrow sectional drawing, (d) ) Is a DD arrow view. It is a fragmentary figure which shows the immersion nozzle of a comparative example, (a) is AA arrow sectional drawing, (b) is BB arrow sectional drawing, (c) is CC arrow sectional drawing, (d) ) Is a DD arrow view. It is a fragmentary figure which shows the immersion nozzle of a comparative example, (a) is AA arrow sectional drawing, (b) is BB arrow sectional drawing, (c) is CC arrow sectional drawing, (d) ) Is a DD arrow view. It is a fragmentary figure which shows the immersion nozzle of a comparative example, (a) is AA arrow sectional drawing, (b) is BB arrow sectional drawing, (c) is CC arrow sectional drawing, (d) ) Is a DD arrow view.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Immersion nozzle 2 Discharge hole 3 Slit 4 Cylindrical bottom part 5 Cylindrical side wall 6 Discharge hole bottom part 7 Discharge hole side wall 8 Discharge hole top part 9 Tip 10 The very vicinity of a discharge hole or a slit 11 Curved surface 22 Magnesia lime refractory 24 Zirconia lime graphite refractory Or zirconia graphite refractory 25 zirconia lime graphite refractory 26 zirconia graphite refractory 27 alumina graphite refractory 28 magnesia lime refractory sleeve 29 joint refractory

Claims (4)

  It has a bottomed cylindrical shape, and two discharge holes are arranged at a position symmetrical to the cylinder at the lower part of the cylindrical side wall, and at least the inner peripheral part of the cylinder including the discharge hole includes magnesia including the tip of the discharge hole. The outer peripheral portion of the cylinder, which is formed of lime-based refractory and includes at least the discharge hole, except for the very vicinity of the discharge hole, is formed of zirconia lime graphite refractory or zirconia graphite refractory, and magnesia at the inner periphery of the cylinder. An immersion nozzle for continuous casting, wherein the lime refractory and the zirconia lime graphite refractory or zirconia graphite refractory on the outer periphery of the cylinder are integrally formed.   It has a bottomed cylindrical shape, and two discharge holes are arranged at a position symmetrical to the cylinder at the bottom of the cylindrical side wall, and a slit that opens to the outside by connecting the bottom of the cylinder and the bottom of both discharge holes is provided. The inner peripheral portion of the cylinder including at least the discharge hole is formed of a magnesia lime refractory including the tip of the discharge hole and the tip of the slit, and is the outer peripheral portion of the cylinder including the discharge hole and including the discharge hole and the slit. The parts other than the vicinity are made of zirconia lime graphite refractory or zirconia graphite refractory, and the magnesia lime refractory at the inner periphery of the cylinder and the zirconia lime graphite refractory or zirconia graphite refractory at the outer periphery of the cylinder are integrally formed. An immersion nozzle for continuous casting characterized by being made.   The immersion nozzle for continuous casting according to claim 1 or 2, wherein the thickness of the magnesia lime refractory at the inner periphery of the cylinder is 7 mm or less.   The upper part of the immersion nozzle is a magnesia lime refractory sleeve at the inner circumference of the cylinder, an alumina graphite refractory at the outer circumference of the cylinder, and an magnesia lime refractory sleeve at the inner circumference of the cylinder. The immersion nozzle for continuous casting according to any one of claims 1 to 3, wherein a sleeve is inserted into the refractory.

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