JP5999383B2 - Lower nozzle of sliding nozzle device - Google Patents

Description

  The present invention relates to a sliding nozzle device, and more particularly to a lower nozzle of the sliding nozzle device.

  A sliding nozzle device is used to control the flow rate when pouring molten steel from the ladle into the tundish and from the tundish into the mold.

  FIG. 1 is a diagram showing a sliding nozzle device. An upper plate 1 is disposed on the lower surface of an upper nozzle disposed in a ladle or tundish, and a lower plate 2 is slidably disposed along with nozzles described below on the lower side of the upper plate 1. A long nozzle 5 (or a submerged nozzle in the case of injecting molten steel into a mold) has a tube-like rectifying nozzle 1 or 2 interposed in the lower part of the lower plate 2 and injects molten steel into the tundish at the lower part thereof. Be joined.

  The rectifying nozzle is arranged between the lower plate 2 and the long nozzle (or immersion nozzle) 5 in order to change the drift of the molten steel generated by the plate restriction between the upper plate 1 and the lower plate 2 into rectification. Intervened in. The two nozzles for rectification are referred to as the intermediate nozzle 3 and the lower nozzle 4, but both perform the same function, so that the intermediate nozzle 3 and the lower nozzle 4 are required to have the same characteristics. In the following description, the lower nozzle 10 including the intermediate nozzle is referred to.

  For the lower nozzle 10, an alumina carbonaceous non-fired brick which is advantageous in spalling resistance, corrosion resistance, cost and the like is generally applied. Since the upper and lower plates 1 and 2 and the lower nozzle 10 are mounted on a sliding device and fixed to the ladle, after the casting is finished, the ladle is moved and maintained with the ladle and used repeatedly for casting.

  The lower nozzle 10 is exposed to a rapid temperature rise because molten steel passes through the inner pipe during use, and spalling cracks are generated.

  In order to suppress the occurrence of cracks, Japanese Patent Application Laid-Open No. 58-104063 (Patent Document 1) and Japanese Patent Application Laid-Open No. 6-277824 (Patent Document 2) obtain a lower nozzle with less cracking from the material surface. Attempts have been made to do so.

  In Japanese Patent Application Laid-Open No. 11-114666 (Patent Document 3), the lower nozzle is constrained from the outside by an iron skin, and further, a reinforcing iron skin is put on the lower part to try to strengthen the lower nozzle from the structural surface. Attempts have been made.

  In JP 2011-161472 A (Patent Document 4), the inner diameter of the casting nozzle is made smaller than the inner diameter of the lower nozzle at the joint between the lower nozzle and the casting nozzle joined to the lower nozzle. Therefore, even if a crack occurs in the lower nozzle, a structure that makes it difficult to suck in air has been proposed.

  Furthermore, in Japanese Patent No. 5129636 (Patent Document 5), the shrinkage rate when cooled from 1500 ° C. to room temperature as a multilayer structure in the radial direction is increased on the inner side in the radial direction and decreased on the outer side, and the difference in the shrinkage rate is described. A proposal has been made to make the ratio 0.25% or less. The invention disclosed in Patent Document 5 assumes an immersion nozzle having no temperature difference between the inner surface and the outer surface of the nozzle, and is used when the inner surface temperature is high and the outer peripheral temperature is low like the lower nozzle. Is not applicable. In addition, the multilayer structure may be difficult to manufacture and is difficult to apply to the lower nozzle.

JP 58-104063 A JP-A-6-277824 JP-A-11-114666 JP 2011-161472 A Japanese Patent No. 5129636

  In recent years, the number of uses required for the lower nozzle has increased remarkably, and slabs have been generated due to the intake of air from cracks, the occurrence of erosion, and the change in the composition of molten steel due to perforations at the erosion sites or intake from the cracks. The problem of quality degradation has occurred. Therefore, in the sliding nozzle device, suppression of intake air from cracks due to repeated use is an important issue from both aspects of stable operation and slab quality.

  However, the attempts disclosed in Patent Document 1 and Patent Document 2 to suppress the occurrence of cracks from the surface of the material cannot completely suppress the occurrence of cracks. Because it was a route, I couldn't keep inspiration.

  Patent Document 3 is intended to suppress the occurrence of cracks by covering the lower nozzle with an iron skin, but when used repeatedly, the iron skin deteriorates due to heat and is sufficient to suppress the occurrence and opening of cracks. It was not possible to obtain sufficient restraining force, and it was not possible to sufficiently prevent intake and melting damage from cracks.

  Patent Document 4 tries to suppress the generation of cracks from the structural surface. However, since the cracks generated in areas other than the fitting portion penetrate through repeated heating, in this case as well, the intake by repeated use is completely eliminated. I couldn't stop it.

  Further, as described above, Patent Document 5 assumes an immersion nozzle having no temperature difference between the inner surface and the outer surface of the nozzle, and is not applicable to the lower nozzle.

  For this reason, under repeated use, there is a limit to improvements from the material and structural aspects only to suppress the occurrence of cracks. Rather, it is a solution from the viewpoint of preventing the occurrence of cracks from inhaling. It is necessary to find out.

  The present invention has been proposed in view of the above-described conventional circumstances, and suppresses intake / melting damage from cracks that occur when the lower nozzle of the sliding nozzle device is repeatedly used, and improves the quality of the slab. The purpose is to plan.

The present invention is a lower nozzle of a sliding nozzle device that is repeatedly used, and has a remaining dimensional change rate of 0.0% to 0.8% by firing at 1500 ° C. for 2 hours in a non-oxidizing atmosphere. It is what.

  The residual dimensional change rate is preferably 0.0% or more and 0.8% or less. If it is less than 0.0%, it is not preferable because intake and melting damage due to crack propagation cannot be suppressed. On the other hand, if it exceeds 0.8%, the expansion at the time of reaction is too large, so that the crack on the outer peripheral side opens and the expansion effect on the inner peripheral surface side is offset, and as a result, it becomes easier to take in air. More preferably, it is 0.05% or more and 0.5% or less.

  By the present invention, it is possible to suppress suction and erosion from cracks that occur when the lower nozzle of the sliding nozzle device is used repeatedly, and to suppress slab trouble due to suction from the lower nozzle during continuous casting, The slab quality can be improved.

The figure which shows the lower nozzle for sliding nozzle apparatuses with which this invention is applied. The figure which shows the relationship between the residual dimensional change rate and the number of intake / melting damage occurrence. The figure which shows the lower nozzle covered with the iron case.

<Discussion>
As described above, most of the lower nozzles crack due to thermal spalling in the initial stage of use. However, even if a crack occurs in the lower nozzle, air intake is not always generated and a melting loss occurs, but it is often observed that a crack occurs but no air intake occurs. Moreover, even if a crack occurs, it is recognized that it does not reach the intake directly, but reaches the intake by repeated use. The frequency of occurrence of intake / melt damage tends to increase when the number of uses exceeds 4ch, and the risk is considered to increase when the number of uses increases after repeated use.

  The following phenomenon can be considered for the phenomenon in which the frequency of occurrence of intake and erosion increases with the number of uses. That is, since the molten steel passes through the tubular inner tube of the lower nozzle, the temperature increases from the outer periphery toward the inner periphery. At this time, a tensile stress acts on the outer peripheral side to generate a crack, but a compressive stress acts on the inner peripheral side, so that the progress of the crack stops in the middle of the thickness direction. However, since there is cooling from the inner peripheral side after the molten steel is discharged, the inner peripheral surface contracts and cracks progress from the inner peripheral surface toward the outer periphery. When this is repeated, it is estimated that the cracks from the outside and the cracks from the inside gradually extend and eventually continue, leading to intake.

  Based on this estimation, a method for suppressing the growth of cracks during use was investigated.

  In other words, an appropriate compressive stress can be generated inside the refractory by intentionally causing a reaction with volume expansion due to the high temperature at the time of discharge of molten steel in the refractory material constituting the lower nozzle, thereby generating cracks. It is considered that the condition that does not progress, that is, the condition that can suppress the intake and melting damage from the crack can be created.

  In other words, if the nozzle can be kept in a compressed state at all times during use, during cooling, even if it cracks from the outer periphery or from the inner periphery, more It is presumed that the crack does not propagate inside the wall thickness and the crack is not connected on the outer peripheral side and the inner peripheral side.

  There is a residual dimensional change rate as a parameter for comparing expansion due to reaction accompanied by volume expansion at high temperature. Therefore, by using two raw materials that cause a reaction with expansion at high temperature, using raw materials that cause a phase transition with expansion at high temperature, or using a metal that reacts with oxygen or nitrogen at a high temperature to cause an expansion reaction. A lower nozzle with a sufficient residual dimensional change rate was created, the outer periphery was covered with a metal case, and the actual machine was used. The relationship between the frequency of intake / melt damage and the residual dimensional change rate was examined.

  As a result, it was confirmed that the lower nozzle with the remaining dimensional change rate in a specific range did not cause intake / melting, although cracks occurred. That is, it came to propose the lower nozzle of the sliding nozzle apparatus whose residual dimensional change rate by baking at 1500 degreeC for 2 hours in a non-oxidizing atmosphere is 0.0% to 0.8%.

<Range>
In the above, the residual line change rate is a value determined under conditions of 1500 ° C. for 2 hours according to JIS R 2208. Since the frequency of suction and erosion from cracks tends to increase after the 4th use of the lower nozzle, the test time is 2 hours, which is 4 times of use, with 30 minutes per use. did. The heating condition is non-oxidizing firing. Heating in an oxidizing atmosphere is not preferable because the carbon contained in the lower nozzle is oxidized. Various methods can be used as the non-oxidizing atmosphere, and examples thereof include a method of firing in a coke breeze and firing in an inert gas such as nitrogen gas or argon gas.

  The residual dimensional change rate is preferably 0.0% or more and 0.8% or less. If it is less than 0.0%, it is not preferable because intake and melting damage due to crack propagation cannot be suppressed. On the other hand, if it exceeds 0.8%, the expansion at the time of reaction is too large, so that the crack on the outer peripheral side opens and the expansion effect on the working surface side is offset, and as a result, it becomes easier to take in air. More preferably, it is 0.05% or more and 0.5% or less.

  It is well known that the remaining dimensional change rate is a general characteristic as a refractory and changes due to various causes. For example, even if the chemical composition is the same, even if the particle size distribution is different, the remaining dimensional change rate changes. Therefore, in applying the present invention, the residual dimensional change rate is set within the appropriate range indicated by the present invention by taking a method such as increasing or decreasing the residual expansion based on the composition of the reference lower nozzle. It is preferable to adjust.

  A case where the value of the residual dimensional change rate is positive is referred to as residual expansion, and conversely, a negative case is referred to as residual shrinkage.

As a method of increasing the residual dimensional change rate, for example, a method of adding an appropriate amount of metal, carbide, nitride, or the like that undergoes volume expansion by reacting with oxygen or nitrogen in the air at a high temperature can be appropriately selected. In addition, a component that causes volume expansion by a reaction at a high temperature is added, such as a reaction that generates spinel by a reaction between MgO and Al ₂ O ₃ . In addition, any other method such as adding a raw material that causes a phase transition accompanying expansion, such as a phase transition from an α phase to a β phase of quartz, can be applied to the product of the present invention. When residual expansion is imparted by a reaction at a high temperature, it is common to use a non-fired material.

  On the other hand, as a method of reducing the remaining dimensional change rate, if the remaining dimensional change rate is increased by the above method, measures such as limiting the amount may be taken. Add raw materials that shrink at high temperatures. Further, any other method such as adding a raw material that promotes sintering shrinkage at high temperature can be adjusted in the direction of residual shrinkage.

  Specifically, the example is shown in Table 1 below.

  The lower nozzle of the sliding nozzle device of the present invention is generally made of an alumina carbon material having excellent spalling resistance. However, in the product of the present invention, characteristic values other than the remaining dimensional change rate can be arbitrarily set within a range that does not impair the spalling resistance and the melt resistance required as the lower nozzle material.

The aggregate material that can be used in the present invention is not particularly limited. Commonly used refractory materials such as clay and SiO ₂ materials can be used.

Further, as the carbon raw material, carbon raw materials such as carbon black, scale graphite, earth graphite, coke powder, anthracite, and powder pitch can be added. If necessary, metals, carbides, nitrides, etc. can also be used, for example, Si, Al or alloys containing Si and Al as metals, SiC, B ₄ C as carbides, Si ₃ N ₄ as nitrides, etc. AlN, BN, etc. can be used.

  As a binder, a phenol resin is generally used, and both a resol type and a novolac type can be used.

  The raw materials mixed in the above range were kneaded and molded to form unfired refractories, which were used in the following examples. As shown in FIG. 3, an iron case 6 may be set around the intermediate nozzle 3 and the lower nozzle 4 (lower nozzle 10) via a mortar, and the outer periphery may be covered with an iron skin.

<Examples and Comparative Examples>
Based on an alumina carbon material based on the mixing of raw materials that react and expand at high temperatures, raw materials that undergo phase transition accompanied by expansion at high temperatures, and metals that react with oxygen and nitrogen at high temperatures to cause expansion reactions. The lower nozzles having the composition shown in Table 1 having various residual dimensional change rates were prepared. The residual dimensional change rate was obtained by calcination in a coke breeze at 1500 ° C. for 2 hours according to JIS R 2208 using a sample having a shape of 50 mm × 50 mm × 50 mm.

  Ten pieces of each material were used as intermediate nozzles for a 300t molten steel ladle sliding nozzle device with the outer periphery covered with a metal case, and the relationship between the occurrence frequency of intake / melting damage and the remaining dimensional change rate was examined. For each material, the average number of use of 10 was 6 charges or more, and it was determined that each nozzle was used repeatedly for the normal number of times.

  The evaluation of intake / melting damage is that if the depth of the inner pipe is 5mm or more deep due to the melting damage along the cracks seen on the cut surface in the vertical direction of the lower nozzle, I saw it. The number of occurrences of intake / melting damage during 10 use was judged to be good.

  The results are shown in FIG. When the residual dimensional change rate was in the range of 0 to 0.8%, the number of occurrences of intake / melting was 1 or less, and the number of occurrences of intake / melting was higher or lower than that.

In Table 1, Example 1, Example 3, and Comparative Example 1 were obtained by changing the amount of metal Al added to the unfired alumina carbon material, and an expansion reaction due to the reaction between the metal Al and N ₂ occurred during heating and remained. Although expansion is given, the value is affected by the amount of added Al, and the residual dimensional change rate tends to increase as the amount of added Al increases.

  In Examples 2 and 5, it is considered that residual expansion is imparted due to the expansion due to phase transition during cooling of zirconia in zirconia and mullite, and Example 4 is in the process of raising the temperature of quartz in raw stone raw material. It is considered that residual expansion is given due to the expansion due to the phase transition.

Example 8 and Comparative Example 3 are alumina, magnesia, and carbon materials containing MgO. Spinel is generated by the reaction of MgO and Al ₂ O ₃ , and residual expansion is imparted due to the expansion due to the reaction. The residual dimensional change rate increased as the amount of added MgO increased, and the residual dimensional change rate of Comparative Example 3 with a higher additive amount of 25% was 0.87%.

  Examples 6, 7, and 9 are combinations of raw materials that were found to be able to impart the above-mentioned residual expansion. In Comparative Example 2, it is presumed that residual shrinkage was caused by using a chamotte material that showed shrinkage behavior by heating.

  As mentioned above, it is possible to suppress suction / melting damage from cracks that occur when the lower nozzle of the sliding nozzle device is used repeatedly, and to suppress slab troubles due to suction from the lower nozzle during continuous casting. It is possible to improve the quality of the slab.

1 Upper plate 2 Lower plate 3 Intermediate nozzle 4 Lower nozzle 5 Long nozzle or immersion nozzle 6 Iron case 10 Lower nozzle

Claims (1)

A lower nozzle of a sliding nozzle device that is repeatedly used, and has a remaining dimensional change rate of 0 to 0.8% after baking at 1500 ° C. for 2 hours in a non-oxidizing atmosphere. .

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