JP2014018821A - Continuous casting method using immersion nozzle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively suppress attachment of nonmetallic inclusions in molten steel to an inner surface of a molten steel passage of an immersion nozzle over a long term.SOLUTION: Antioxidant, whose melting temperature is 1100-1350°C and viscosity at 1400°C is 10 Pa s or more, is applied in a thickness of 0.3 mm or more to an inner surface of a molten steel passage of an immersion nozzle 6. Casting is started after preheating under condition that time during which it is 1200°C or more is 120 minutes or less in preheating in which the highest atmospheric temperature of the inner surface of the molten steel passage is 1100°C or more.

Description

  The present invention relates to a method for continuously casting a molten metal such as aluminum killed steel, which is likely to be clogged with high melting point non-metallic inclusions, using an immersion nozzle.

In continuous casting of steel, clogging of the inner surface of the molten steel flow path of the immersion nozzle due to adhesion of high melting point non-metallic inclusions typified by alumina has a great influence on operation and slab quality.
Therefore, various countermeasure techniques for preventing the clogging of the immersion nozzle have been proposed.

  For example, Patent Document 1 proposes a spinel-periclase-graphite refractory that forms a dense inner surface by a chemical reaction at a high temperature during casting. Patent Document 2 proposes a refractory made of graphite and magnesia and / or spinel that contains a low melting point beryl and forms a low melting point layer on the inner surface.

  On the other hand, some of the inventors have proposed in Patent Document 3 an invention in which the inclusion of alumina inclusions is prevented by containing a small amount of CaO or the like in alumina graphite, and the effect is further increased by using electricity in combination. ing. Further, some of the inventors have proposed an invention in Patent Document 4 in which an AC pulsed current is passed through an immersion nozzle to prevent adhesion of non-metallic inclusions.

  Patent Document 5 proposes a method of suppressing the adhesion of non-metallic inclusions by energizing an immersion nozzle having an antioxidant coated on the inner surface.

  Although the methods proposed in Patent Documents 1 to 5 each exhibit a certain effect, there are problems that the effect is limited or the casting conditions that exhibit the effect are limited.

Japanese Patent No. 3358899 JP 2002-035904 A JP 2010-201504 A International Publication No. 2008-090649 Pamphlet JP 2004-330256 A

  The problem to be solved by the present invention is that the conventional technique has a limited effect or a limited casting condition for exhibiting the effect.

  As a result of repeated research and development, the inventors have formed and maintained a slag layer that coats the inner surface of the molten steel flow path of the immersion nozzle, thereby effectively adhering non-metallic inclusions in the molten steel to the inner surface of the molten steel flow path. We found that it was possible to control the slag layer, and searched for advantageous conditions for maintaining the slag layer. The slag layer is a semi-molten layer having a liquid phase or glass phase, and the presence of the liquid phase or glass phase improves wettability with molten steel, resulting in adhesion of non-metallic inclusions such as alumina. It becomes difficult to do.

The present invention was made by searching for advantageous conditions for maintaining the slag layer based on the above findings of the inventors,
In order to effectively suppress the adhesion of non-metallic inclusions in the molten steel to the inner surface of the molten steel flow path of the immersion nozzle over a long period of time,
Applying an antioxidant having a melting temperature of 1100 to 1350 ° C. and a viscosity at 1400 ° C. of 10 Pa · s or more to the inner surface of the molten steel flow path of the immersion nozzle with a thickness of 0.3 mm or more,
The main feature of the steel is that the casting is started after preheating under the condition that the time of 1200 ° C. or more is 120 minutes or less among the preheating in which the maximum atmospheric temperature of the molten steel flow path inner surface is 1100 ° C. or more. It is a continuous casting method.

  In the present invention, there is provided an immersion nozzle in which an antioxidant having a melting temperature of 1100 to 1350 ° C. and a viscosity at 1400 ° C. of 10 Pa · s to 1000 Pa · s is applied to the inner surface of the molten steel flow channel in a thickness of 0.3 mm or more. use. And, in use, the preheating under the condition that the maximum atmosphere temperature on the inner surface of the molten steel flow channel is 1100 ° C. or higher and the time of 1200 ° C. or higher is 120 minutes or shorter, so that the molten steel flow channel of the submerged nozzle The antioxidant applied to the inner surface does not flow down during preheating, and adhesion of nonmetallic inclusions can be suppressed for a long time.

In the present invention, the immersion nozzle, C: 11 to 45 wt%, Al ₂ O _3: 40~80 wt%, CaO: 1 to 7 if formed by graphite refractory containing mass%, antioxidant The low melting point phase is formed on the working surface on which the agent is applied, and the action of helping to maintain the slag layer that coats the inner surface of the molten steel flow path occurs.

  According to the present invention, non-metallic inclusions such as alumina adhere to the inner surface of the molten steel channel over a long period of time by forming and maintaining a slag layer on the working surface of the refractory on the inner surface of the molten steel channel of the immersion nozzle. Can be suppressed.

It is a schematic block diagram explaining the continuous casting method using the immersion nozzle of this invention. It is the longitudinal cross-sectional view which showed an example of the immersion nozzle used for the continuous casting method of this invention.

  An object of the present invention is to provide an antioxidant that is applied to the inner surface of a molten steel channel for the purpose of effectively suppressing the adhesion of nonmetallic inclusions in the molten steel to the inner surface of the molten steel channel of an immersion nozzle over a long period of time. This is achieved by preventing the water from flowing down during preheating.

Hereinafter, the form for implementing the continuous casting method of this invention is demonstrated.
FIG. 1 is a schematic configuration diagram illustrating the continuous casting method of the present invention. After molten steel 1 is supplied from a ladle 2 to a tundish 3, a mold 7 is passed through an upper nozzle 4, a sliding gate 5, and an immersion nozzle 6. The primary cooling is carried out. The molten steel 1 injected into the mold forms a solidified shell 8 on the outer periphery by cooling from the inner surface of the mold. The solidified shell 8 increases in thickness as it is pulled out from the mold 7, and after being pulled out from the mold 7, it is secondarily cooled and completely solidified into a slab. In addition, 9 in FIG. 1 is the mold powder supplied to the upper surface of the molten steel in the mold 7.

-1st invention The inventors think that the origin of the slag layer which exists so as to coat the molten steel flow path inner surface of an immersion nozzle is the antioxidant applied in order to prevent the oxidation during preheating. As a result, it was found that the antioxidant did not flow down during the preheating, which was a necessary condition for maintaining the slag layer.

  As a result of the inventors' experiments and research, when the following conditions are adopted, the antioxidant does not flow down during preheating, and the adhesion of nonmetallic inclusions to the inner surface of the molten steel flow path of the immersion nozzle tends to decrease. I found.

-Necessary conditions for maintaining the slag layer An antioxidant having a high melting temperature of 1100 ° C or higher and a viscosity of 10 Pa · s or higher at 1400 ° C is applied to the inner surface of the molten steel channel of the immersion nozzle. Apply at a thickness of 3 mm or more. And the preheating of the immersion nozzle is performed under a condition where the time during which the atmosphere temperature on the inner surface of the molten steel flow path is 1200 ° C. or higher is not excessive as 120 minutes or less.

The first invention has been made based on the results of the inventors' experiments and research,
An antioxidant having a melting temperature of 1100 to 1350 ° C. and a viscosity at 1400 ° C. of 10 Pa · s or more is applied to the inner surface of the molten steel passage of the immersion nozzle 6 with a thickness of 0.3 mm or more,
Casting is started after preheating under a condition that a time of 1200 ° C. or more is 120 minutes or less among preheating in which the maximum atmospheric temperature on the inner surface of the molten steel flow path is 1100 ° C. or more.

  Here, the antioxidant is a glaze-like glass coating agent applied to the inner and outer surfaces of the immersion nozzle in order to prevent the oxidation of carbonaceous materials (graphite, etc.) in the refractory, and is mainly composed of SiO2, B2O3, etc. Ingredients.

  In the first invention, the upper limit of the melting temperature of the antioxidant is regulated to 1350 ° C. When the temperature exceeds 1350 ° C., the whole or a part of the antioxidant melts and covers the inner surface of the molten steel flow path of the immersion nozzle. This is because the function as an antioxidant, which prevents oxidation of the refractory, is reduced. Moreover, the lower limit is set to 1100 ° C., because when the temperature is lower than 1100 ° C., the antioxidant easily flows down during preheating of the immersion nozzle.

  The melting temperature of the antioxidant is that after the antioxidant is completely melted in an oxidizing atmosphere, the sample is crushed to an average particle size of 10 to 30 μm and shaped into a cylindrical green compact with a diameter and height of 8 mm. , Defined as the temperature at which the surface shape of the part not in contact with the graphite substrate becomes a smooth curved surface with continuous curvature when heated gradually at a heating rate of 2 ° C per minute on a graphite substrate in an Ar atmosphere To do.

  The reason why the viscosity at 1400 ° C. of the antioxidant is 10 Pa · s or more is that if it is less than 10 Pa · s, the antioxidant tends to flow off during preheating of the immersion nozzle. Although the upper limit is not particularly defined, it is preferably 1000 Pa · s or less from the viewpoint of ensuring the spreadability of the glass coating.

  The reason why the coating thickness of the antioxidant is set to 0.3 mm or more is that when the thickness is less than 0.3 mm, the antioxidant tends to flow down during preheating of the immersion nozzle. The coating thickness is more preferably 0.4 mm or more. The upper limit of the thickness at which the antioxidant is applied is not particularly defined, but if it exceeds 1 mm, it is generally difficult to apply and dry repeatedly.

  In addition, the preheating of the immersion nozzle so that the maximum atmospheric temperature on the inner surface of the molten steel channel reaches 1100 ° C. or higher is because the antioxidant does not sufficiently melt in the case of weak preheating that does not reach 1100 ° C. This is because the effects of the present invention are impaired, and the thermal shock at the start of casting is increased, which may break the immersion nozzle.

  The reason why the upper limit of the time during which the atmospheric temperature of the molten steel flow path inner surface is 1200 ° C. or higher is set to 120 minutes is that the antioxidant tends to flow down if preheated for a long time under high temperature conditions. Even if the lower limit of the time is 0, it is sufficient if the maximum temperature reaches 1100 ° C. or higher, but from the viewpoint of ensuring sufficient preheating, it is desirable that the time is 1200 ° C. or higher and is 15 minutes or longer. .

Second Invention The inventors reduced the amount of non-metallic inclusions that adhere to the slag surface and melt into the slag by applying a predetermined current between the immersion nozzle and the molten steel passing through the flow path. The second invention was established by discovering that the slag layer originating from the antioxidant is easily maintained as it is.

That is, in the second invention, a graphite refractory containing 11 mass% or more of carbon is disposed on the inner surface of the flow path of the immersion nozzle 6, and one electrode 10 is connected to the immersion nozzle 6, and the inside of the tundish 3 The other electrode 11 is immersed in the molten steel 1 to form an energization circuit between the immersion nozzle 6 and the molten steel 1 passing through the flow path, and the absolute value of the average current density in the immersion nozzle 6 is 0.5. It is characterized by casting while energizing so that it becomes ˜15 mA (milliampere) / cm ² . The one electrode 10 may be installed on the graphite-containing refractory of the submerged nozzle body by the method described in, for example, Japanese Patent Application Laid-Open No. 2005-199339.

  In FIG. 1, 12 is a wiring connecting one electrode 10 and the other electrode 11, 13 is a power supply device provided in the middle of the wiring 12, and 14 is an insulation provided between the immersion nozzle 6 and the sliding gate 5. Refractory material 15 is an insulating refractory material provided between the tundish 3 and the other electrode 11.

  In the second invention, the graphite refractory containing 11% by mass or more of carbon is arranged on the inner surface of the molten steel flow path of the immersion nozzle because the electrical conductivity decreases when the carbon concentration is less than 11% by mass. This is because smooth energization becomes difficult.

Also, casting while energizing so that the absolute value of the average current density in the immersion nozzle is 0.5 to 15 mA / cm ² causes some ion generation and mass transfer such as iron ions and oxygen ions, and the molten steel and slag layer This is because it is necessary to pass a current of at least 0.5 mA / cm ² or more in order to improve the wettability. On the other hand, not only is a large current exceeding 15 mA / cm ² unnecessary, but conversely it has been experimentally confirmed that the effect is reduced.

  Here, the “average current density in the immersion nozzle” means the current density obtained by dividing the average current value flowing between the immersion nozzle and the molten steel when a voltage is applied by the total area of the nozzle wall surface in contact with the molten steel. Means.

  The slag layer originated from antioxidants loses its effectiveness when non-metallic inclusions mainly composed of alumina adhere to the surface. It maintains its effectiveness over time. That is, the first invention is further strengthened by the second invention.

Third invention When the inventors use an AC pulse-shaped current waveform having an appropriate period and current density, the molten iron is ionized and penetrates into the slag layer on the inner surface of the immersion nozzle, so that nonmetallic inclusions penetrate. It has been found that the effect of maintaining the slag layer over a long period of time is produced by inhibiting the melting point of the slag layer that progresses due to the above. That is, the second invention is further strengthened by the third invention.

3rd invention is made | formed based on the said knowledge,
Between the electrodes 10 and 11 of the second invention, 3 to 200 msec is set as one cycle, and a pulsed voltage whose polarity is switched between positive and negative within this cycle is applied. The period for the negative electrode is made longer than the period for the positive electrode, or the absolute value of the potential during the period when the immersion nozzle 6 is the negative electrode is made larger than the absolute value of the potential during the period of the positive electrode, or both By carrying out, the current average potential in the immersion nozzle 6 is controlled to a negative voltage, and energization is performed so that the absolute value of the current density is 10 to 200 mA / cm ² during the period in which the immersion nozzle 6 is a negative electrode. is there.

  In the third invention, the period of the AC pulse waveform is set to 3 to 200 msec because the electrochemical reaction such as ionization (oxidation) of molten iron or reduction of iron ions does not sufficiently proceed when the period is less than 3 msec. On the other hand, if it exceeds 200 msec, adverse effects such as the generation of CO gas at the positive electrode and the movement of oxygen ions at the negative electrode, which are caused by the reduction of oxides by carbon, become obvious.

Further, in addition to controlling the voltage at which the time average potential at the immersion nozzle is negative as described above, the energization is such that the absolute value of the current density is 10 to 200 mA / cm ² during the period when the immersion nozzle is a negative electrode. This is because the phenomenon that the molten iron is ionized by this energization and enters the slag layer occurs preferentially, and the slag layer is maintained for a long time. The condition that the time average potential of the immersion nozzle is positive is not desirable because it facilitates the reduction reaction of iron ions to be superior to the ionization reaction of molten iron.

When the absolute value of the current density during the period in which the immersion nozzle is a negative electrode is less than 10 mA / cm ² , the molten iron ionization reaction does not proceed sufficiently. In addition, an excessive current so that the absolute value exceeds 200 mA / cm ² is not necessary, and has an adverse effect of migration of oxygen ions. Furthermore, it is not preferable in that a large-scale energization facility is required.

-4th invention Usually, graphite refractories, such as an alumina graphite and spinel graphite which have an alumina and carbon as a main component, are used for an immersion nozzle. The inventors have added a trace amount of CaO to this graphite refractory, whereby a low melting point phase is formed on the working surface coated with the antioxidant, and the effect of helping to maintain the slag layer on the inner surface of the immersion nozzle occurs. I found out.

The fourth invention has been made based on the findings, C in the first to third invention, the refractory forming the immersion nozzle, as a chemical composition: 11 to 45 wt%, Al ₂ O ₃ : A graphite refractory containing 40 to 80% by mass and CaO: 1 to 7% by mass.

  As in the fourth aspect of the invention, the low melting point phase generated by adding a trace amount of CaO also has a function of assisting smooth energization as an ion path during energization. In other words, the first to third inventions are further strengthened by the fourth invention.

  In the fourth invention, the refractory contains 11 to 45% by mass of C, which is the main component of graphite, as the chemical composition because if the content is less than 11% by mass, it becomes weak against thermal shock. On the other hand, if the content exceeds 45% by mass, it becomes weak against oxidation and erosion. A more preferable range of the C concentration is 15 to 40% by mass.

Further, to contain Al ₂ O ₃ 40 to 80% by weight, Al ₂ O ₃ is a main component of the refractory, if the concentration is less than 40 wt%, reduces the corrosion resistance of the refractory, Furthermore, the CaO-containing effect is impaired. Conversely, if it exceeds 80% by mass, the refractory is vulnerable to thermal shock.

  The reason why 1 to 7% by mass of CaO is contained is that if it is less than 1% by mass, the characteristic that a low melting point phase is formed on the operating surface by CaO is impaired. Conversely, if it exceeds 7% by mass, the corrosion resistance and the thermal shock resistance deteriorate significantly. A more preferable range of the CaO concentration is 2 to 5% by mass.

-Fifth Invention The inventors have found that the effect of the fourth invention can be more stably exhibited by using spinel graphite having chemical stability superior to alumina graphite as a basic material. By using spinel graphite as the basic material, the refractory can be kept healthy, so that the slag layer formed on the working surface is easily maintained.

  That is, since spinel graphite is chemically more stable than general alumina graphite, the effect of containing a trace amount of CaO clearly appears. Although magnesia graphite is also excellent in chemical stability, it is not suitable as a material for the immersion nozzle because it is vulnerable to thermal shock. Further, in the case of magnesia graphite, the effect of containing CaO does not occur.

Furthermore, spinel graphite is advantageous for forming a slag layer on the inner surface of the immersion nozzle because the melting point reduction when SiO _{2 as} the main component of the antioxidant permeates is larger than that of alumina graphite.

  5th invention is made | formed based on the said knowledge, and makes the said graphite-like refractory further spinel graphite containing MgO: 6-25 mass%.

  In the fifth invention, MgO is contained in an amount of 6 to 25% by mass. If the MgO concentration is less than 6% by mass, depending on the balance with the alumina concentration, the spinel approaches the boundary with the corundum phase region and is stable. It is because it becomes difficult to maintain. Furthermore, if the MgO concentration is excessively reduced, the excellent corrosion resistance of the spinel is impaired. Conversely, when the MgO concentration exceeds 25% by mass, the refractory becomes vulnerable to thermal shock. A more preferable range of the MgO concentration is 8 to 20% by mass.

Alumina, along with magnesia, is a component of spinel and the main component of the refractory. If the Al ₂ O ₃ concentration is less than 40% by mass, the concentration of magnesia, which is the other spinel component, becomes too high, and approaches the boundary with the MgO phase region, so that a stable spinel is maintained. Becomes difficult. Conversely, if the Al ₂ O ₃ concentration exceeds 80% by mass, the relative magnesia concentration becomes too low, making it difficult to maintain a stable spinel. A more preferable range of Al ₂ O ₃ concentration is 51 to 70% by mass.

From the viewpoint of maintaining a stable spinel, the concentration balance of alumina and magnesia is preferably MgO / Al ₂ O ₃ of 0.10 to 0.65 in terms of mass%.

  In the first to fifth inventions, when the purity of Ar gas flowing in the molten metal flowing in the molten steel flow path of the immersion nozzle is further increased to 99.99% or more and the oxygen concentration is decreased to 5 ppm or less, non- The effect of preventing adhesion of metal inclusions is stabilized.

  This is because by increasing the purity of Ar gas, the interfacial tension between Ar gas and the molten metal increases, and the Ar gas film is stably maintained in the gap between the molten metal and the inner surface of the immersion nozzle. It is.

  As a result, the contact opportunity between the molten metal and the immersion nozzle refractory itself decreases, and the amount of nonmetallic inclusions in the molten metal adhering to the inner surface of the molten steel flow path of the immersion nozzle decreases. A more preferable result is obtained when the purity of Ar gas is 99.995% or more and the oxygen concentration is 3 ppm or less.

Next, examples and comparative examples of the present invention will be described.
In the following examples and comparative examples, a vertical bending slab continuous casting machine having a mold thickness of 0.3 m and a mold width of 1.2 to 1.6 m is used, and the casting speed excluding the unsteady part is 1.3 to 1. Cast at 8 m / min.

  At that time, as shown in FIG. 1, from the upper plate 5a of the three-layer sliding gate 5 arranged on the upstream side of the immersion nozzle 6, a standard (concentration is 99.999% or more and oxygen concentration is 3 ppm or less). Casting was performed while flowing Ar gas through the molten steel flow path of the immersion nozzle 6 by flowing Ar gas satisfying the mass ratio). Further, the Ar gas having a purity of 99.90% and an oxygen concentration of 7 ppm was cast in the same manner.

  Cast steel grade is mass%, C concentration is 0.02-0.05%, Si concentration is 0.01-0.04%, Mn concentration is 0.3-0.6%, sol.-Al concentration Is 0.02 to 0.06% aluminum killed low carbon steel.

  In addition, the immersion nozzle used was normally used for continuous casting of slabs having the shape and dimensions shown in FIG. 2 and was provided with a pair of discharge holes facing the vicinity of the bottom of the cylindrical main body. The shape is made of a graphite refractory.

  In addition, as shown in FIG. 1, the energization in the second and third embodiments was performed by using an alumina graphite rod immersed in the tundish 3 as the other electrode 11 and on the upper part of the immersion nozzle 6. One electrode 10 was attached.

  The adhesion thickness of the nonmetallic inclusions on the inner surface of the molten steel flow path of the immersion nozzle was recovered by collecting the immersion nozzle through which 500 to 900 ton of molten steel passed continuously, and comparing and evaluating the average adhesion thickness of the inner surface of the molten steel flow path. . The casting test for evaluation was performed several times, and the average value was used for evaluation.

  Tables 1 to 4 below show examples of the present invention, and Table 5 shows comparative examples of the present invention. Table 6 below shows the chemical composition and physical properties of the antioxidants listed in Tables 1-5.

  In Tables 1 to 5 below, AG represents alumina graphite, and SpG represents spinel graphite. In addition, the immersion nozzle inner surface inclusion adhesion index in the following Tables 1 to 5 is a unit from the result of cutting the immersion nozzle after casting and measuring the adhesion thickness of nonmetallic inclusions on the inner surface of the molten steel flow path. The adhesion thickness per molten steel passing amount is calculated, and the result of Comparative Example V is indexed as 20.

  Below, the effect of each Example is demonstrated, contrasting with a comparative example.

-Examples A and B
Examples A and B in Table 1 are examples that satisfy the requirements defined in the first invention. In each of Examples A and B, an antioxidant was applied to the inner surface of the molten steel flow channel of the immersion nozzle made of alumina graphite under the conditions satisfying the requirements specified in the first invention, and the requirements specified in the first invention were satisfied. This is an example in which aluminum killed steel is continuously cast after preheating the immersion nozzle under conditions.

  In these Examples A and B, the slag layer formed by the antioxidant at the start of casting is formed on the inner surface of the immersion nozzle because the application of the antioxidant and the preheating conditions of the immersion nozzle satisfy the requirements specified in the first invention. It remained, and the adhesion of non-metallic inclusions during casting could be reduced.

  Specifically, Examples A and B have immersion nozzle inner surface inclusion adhesion indexes of 16 and 17, and use the same immersion nozzle and do not satisfy the requirements defined in the first invention. X had an index of inclusion on the inner surface of the immersion nozzle of 20, 21, 20. That is, in Examples A and B, compared to Comparative Examples V, W, and X, the adhesion thickness of the nonmetallic inclusions on the inner surface of the molten steel flow path of the immersion nozzle after casting could be reduced by about 20%.

  In Comparative Examples V and W, the melting start temperature of the antioxidant used was lower than 1100 ° C. and the coating thickness was as thin as 0.2 mm compared to Examples A and B, respectively. This is an example in which the inner surface slag layer is not sufficiently maintained during casting and adhesion of non-metallic inclusions is increased.

  In Comparative Example X, since the preheating time of the immersion nozzle was too long as 150 minutes compared to Example B, the antioxidant applied to the inner surface of the molten steel flow path of the immersion nozzle did not remain sufficiently at the start of casting. This is an example in which adhesion of non-metallic inclusions is increased.

-Examples C and D
Examples C and D in Table 1 are examples that satisfy the requirements defined in the first and second inventions. Examples C and D use the same immersion nozzle as in Examples A and B, respectively, and the conditions for applying the antioxidant and the preheating conditions for the immersion nozzle are the same as in Examples A and B, and are defined in the second invention. It evaluates the effect of energization that satisfies the requirements.

  Example C was energized such that the immersion nozzle was a negative electrode, and Example D was energized so that the immersion nozzle was a positive electrode. As a result, in Examples C and D, the immersion nozzle inner surface inclusion adhesion index was 13, and in contrast to Examples A and B in which the index was 16 and 17, the nonmetallic metal on the inner surface of the molten steel flow path of the immersion nozzle after casting The thickness of inclusions was reduced by about 20%.

-Examples E and F
Examples E and F in Table 1 are examples that satisfy the requirements defined in the first to third inventions. Examples E and F use the same immersion nozzle as in Examples A and B, respectively, and the conditions for applying the antioxidant and the preheating conditions for the immersion nozzle are the same as in Examples A and B, and are defined in the third invention. It evaluates the effect of energization that satisfies the requirements.

  In Examples E and F, the submerged nozzle inner surface inclusion adhesion index was 11 and 12, and the energization effect was larger than that of Examples C and D in which the index was 13, and in Examples A and B in which the index was 16, 17. On the other hand, the adhesion thickness of the nonmetallic inclusions on the inner surface of the molten steel flow path of the immersion nozzle after casting could be reduced by about 30%.

Example G
Example G in Table 2 is an example that satisfies the requirements defined in the first, second, and fourth inventions. In Example G, the material of the immersion nozzle is changed to alumina graphite to which a small amount of CaO defined in the fourth invention is added to Example C.

  As a result, in Example G, the immersion nozzle inner surface inclusion index is 10 and the immersion nozzle inner surface inclusion index is 13, compared to Example C, the non-metal on the inner surface of the molten steel flow channel of the immersion nozzle after casting. The thickness of inclusions was reduced by about 20%.

-Examples H and I
H and I in Table 2 are examples that satisfy the requirements defined in the first to fourth inventions. In Examples H and I, only the material of the immersion nozzle is changed to alumina graphite to which a small amount of CaO defined in the fourth invention is added to Examples E and F, respectively.

  As a result, in Examples H and I, the immersion nozzle inner surface inclusion adhesion index is 8, and compared to Examples E and F in which the index is 11 and 12, the immersion nozzle after casting is not attached to the inner surface of the molten steel flow path. The adhesion thickness of metal inclusions could be reduced by about 30%.

  The effect of reducing the adhesion thickness of non-metallic inclusions on the inner surface of the molten steel flow path of the immersion nozzles of Examples H and I is large because of a combination of proper energization and a refractory that satisfies the requirements specified in the fourth invention. It shows that it exhibits a synergistic effect.

・ Example J
Example J in Table 2 is an example that satisfies the requirements defined in the first, second, fourth, and fifth inventions. In Example J, the material of the immersion nozzle is changed to spinel graphite to which MgO and a small amount of CaO specified in the fourth and fifth inventions are added to Example D.

  As a result, in Example J, the immersion nozzle inner surface inclusion index is 9 and the immersion nozzle inner surface adhesion index is 13, compared to Example D, the non-metal on the inner surface of the molten steel flow path of the immersion nozzle after casting. The thickness of inclusions was reduced by about 30%.

-Examples K and L
Example K in Table 2 and Implementation Low L in Table 3 are examples that satisfy the requirements defined in the first to fifth inventions. In Examples K and L, only the material of the immersion nozzle was changed to spinel graphite to which MgO and a small amount of CaO defined in the fourth and fifth inventions were added to Examples E and F, respectively.

  As a result, in Examples K and L, the immersion nozzle inner surface inclusion adhesion index was 6, and compared to Examples E and F with the index of 11 and 12, the immersion nozzle after casting was not attached to the inner surface of the molten steel flow path. The adhesion thickness of metal inclusions could be reduced by about 50%.

  The effect of reducing the adhesion thickness of inclusions on the inner surface of the molten steel flow path of the immersion nozzles of Examples K and L is large because of the combination of proper energization and a refractory that satisfies the requirements specified in the fourth and fifth inventions. It shows that it exhibits a synergistic effect.

-Example M
Example M in Table 3 is an example that satisfies the requirements defined in the first and fourth inventions. In Example M, the energization specified in the second and third inventions was not performed, but as an effect of combining the first and fourth inventions, the immersion nozzle inner surface inclusion adhesion index was 13, and the index was 13. The effect of preventing the adhesion of non-metallic inclusions to the inner surface of the molten steel flow channel of the immersion nozzle of the same level as in Examples C and D was obtained.

Example N
Example N in Table 3 is an example that satisfies the requirements defined in the first, second, and fourth inventions. In Example N, energization was performed under the condition that the immersion nozzle was a negative electrode.

  In Example N, although the energization effect specified in the third invention was not obtained, the immersion nozzle inner surface inclusion adhesion index was 11 as an effect combining the requirements specified in the first, second and fourth inventions, The effect of preventing non-metallic inclusions from adhering to the inner surface of the molten steel flow path of the immersion nozzle having the same index as those of Examples E and F having the index of 11 and 12 was obtained.

-Example O
Example O in Table 3 is an example that satisfies the requirements defined in the first, fourth, and fifth inventions. In Example O, the energization specified in the second and third inventions was not performed, but as a combined effect satisfying the three requirements of the first, fourth and fifth inventions, the immersion nozzle inner surface inclusion adhesion index was 11, The effect of preventing non-metallic inclusions from adhering to the inner surface of the molten steel flow channel of the immersion nozzle was obtained to the same degree as in Examples E and F having the same index of 11 and 12 and Example N having the same index of 11.

-Example P
Example P in Table 3 is an example that satisfies the requirements defined in the first, second, fourth, and fifth inventions. In Example P, energization was performed under the condition that the immersion nozzle became a negative electrode.

  In Example P, although the energization effect defined in the third invention was not obtained, the immersion nozzle inner surface inclusion adhesion index was 8, which was an effect commensurate with the first, second, fourth and fifth inventions. Obtained. That is, the effect of preventing the adhesion of non-metallic inclusions to the inner surface of the molten steel flow path of the immersion nozzle having the same immersion nozzle inner surface inclusion index of 8 as Examples H and I was obtained.

-Examples Q to U
Examples Q to U in Table 4 have a purity of 99.90% and an oxygen concentration of only Ar gas blown from the upper plate 5a of the sliding gate 5 under the same casting conditions as those of Examples A, C, E, H, and J. This is an example of changing to 7 ppm.

  In these Examples Q, R, S, T, and U, the immersion nozzle inner surface inclusion index was 19, 15, 13, 9, 11, and the immersion nozzle inner surface index was 16, 13, 11, 8, and 9. Compared to Examples A, C, E, H, and J, the adhesion thickness of nonmetallic inclusions on the inner surface of the molten steel flow path of the immersion nozzle after casting was increased by about 20%.

  However, the immersion nozzle inner surface inclusion adhesion index of Comparative Example V cast under the same casting conditions as Example A is 20. In addition, under the same casting conditions as in Comparative Example W and Comparative Example W cast under the same casting conditions as in Comparative Example V and Example B, similarly to Examples Q to U, only Ar gas to be blown in had a purity of 99.90% and an oxygen concentration of In Comparative Examples Y and Z changed to 7 ppm, the immersion nozzle inner surface inclusion adhesion index was 24 and 25, and non-metallic inclusions on the inner surface of the molten steel flow path of the immersion nozzle after casting with respect to Comparative Examples V and W The deposit thickness increased by about 20%.

  Accordingly, when the Ar gas to be blown is the same, by applying the requirements of the present invention, the adhesion thickness of non-metallic inclusions on the inner surface of the molten steel flow channel of the immersion nozzle after casting compared to the case of not applying the requirements of the present invention Can still be suppressed.

  Needless to say, the present invention is not limited to the above-described examples, and the embodiments may be appropriately changed within the scope of the technical idea described in the claims.

DESCRIPTION OF SYMBOLS 1 Molten steel 4 Upper nozzle 5 Sliding gate 6 Immersion nozzle 10 One electrode 11 The other electrode

Claims (5)

Applying an antioxidant having a melting temperature of 1100 to 1350 ° C. and a viscosity at 1400 ° C. of 10 Pa · s or more to the inner surface of the molten steel flow path of the immersion nozzle with a thickness of 0.3 mm or more,
A continuous casting method for steel, wherein casting is started after preheating under a condition that a time of 1200 ° C. or more is 120 minutes or less among preheating in which the maximum atmospheric temperature of the molten steel flow path inner surface is 1100 ° C. or more. . A graphite refractory containing 11 mass% or more of carbon is disposed on the inner surface of the flow path of the immersion nozzle, and one electrode is connected to the immersion nozzle, and the other electrode is immersed in the molten steel in the tundish, An energization circuit is configured between the immersion nozzle and the molten steel passing through the flow path of the immersion nozzle,
^{2. The} continuous casting method using an immersion nozzle according to claim 1, wherein casting is performed while energizing so that an absolute value of an average current density in the immersion nozzle is 0.5 to 15 mA (milliampere) / cm < ² >. A period of 3 to 200 msec is applied between the electrodes, and a pulsed voltage whose polarity is switched between positive and negative within this period is applied,
Within one cycle, the period during which the immersion nozzle is a negative electrode is longer than the period during which the immersion nozzle is a positive electrode, and / or the absolute value of the potential during the period during which the immersion nozzle is a negative electrode is the potential during the period during which the positive electrode is positive. By controlling it to be larger than the absolute value of the voltage, the time average potential in the immersion nozzle is controlled to a negative voltage,
The continuous casting method using the immersion nozzle according to claim 2, wherein energization is performed so that an absolute value of a current density is 10 to 200 mA / cm ² during a period in which the immersion nozzle is a negative electrode. The refractory forming the immersion nozzle is a graphite refractory containing C: 11 to 45% by mass, Al ₂ O ₃ : 40 to 80% by mass, and CaO: 1 to 7% by mass as the chemical composition. A continuous casting method using the immersion nozzle according to any one of claims 1 to 3.   5. The continuous casting method using an immersion nozzle according to claim 4, wherein the graphite refractory is spinel graphite further containing MgO: 6 to 25% by mass.

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