JP2012055911A - Method for producing continuously-cast slab - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a continuously-cast slab, by which the deposition suppressing effect of oxide on an inner surface of immersion nozzles is obtained stably and equally to each immersion nozzle by using an apparatus of a simple constitution in a steel continuous casting machine having a plurality of strands.SOLUTION: The method for producing the continuously-cast slab is characterized in that: each immersion nozzle corresponding to each strand is used as one electrode, one common electrode as an opposing pole of each of the electrode is immersed in molten steel in a tundish, thus an electric circuit is constituted for each strand and a power source is arranged in each electric circuit; current having a current value of 10-300 A and a cycle length of 6-20 ms, and having a pulse waveform in which the positive and negative signs of the voltage are alternately changed is supplied with the same cycle length, phase and voltage to each electric circuit from each power source; and the period in which the immersion nozzle forms a negative electrode in one period of the pulse waveform is set to be longer than the period in which the immersion nozzle forms a positive electrode.

Description

  TECHNICAL FIELD The present invention relates to a method for producing a continuous cast slab, and in particular, is used for a continuous casting machine having a plurality of strands, and oxides on the inner surface of an immersion nozzle used when pouring molten steel into a mold of each strand. It is related with the manufacturing method of the continuous cast slab which can suppress the obstruction | occlusion of the inner hole by adhesion of.

  Generally, it is an unavoidable problem that the inner hole of the immersion nozzle for molten steel injection is blocked during continuous casting of steel. The inner hole blockage of the immersion nozzle is caused by the inclusions in the molten steel being removed from the molten steel and adhering to the surface of the refractory constituting the inner wall of the immersion nozzle in the process of passing the molten steel through the interior of the immersion nozzle. It occurs when inclusions in the molten steel further adhere and deposit starting from the inclusions (for example, Non-Patent Document 1).

  Here, inclusions in the molten steel are mainly alumina. When the inner hole of the immersion nozzle is blocked, continuous casting may be interrupted due to the shortage of molten steel supplied to the mold. In addition, when the inclusions adhered and deposited on the inner surface of the immersion nozzle peel off from the inner surface of the immersion nozzle, the peeled inclusions enter the mold together with the molten steel passing through the immersion nozzle and remain inside the slab. May cause defects due to inclusions in the product.

  As a method of suppressing the adhesion of inclusions to the inner surface of the immersion nozzle, there are a method of blowing argon gas from the molten steel flow control mechanism (sliding nozzle) and the upper nozzle, and a method of blowing inert gas into the molten steel passing through the immersion nozzle. For example, it is disclosed in Patent Document 1 and Patent Document 2. The method disclosed in Patent Document 1 is a method of adjusting the amount of inert gas blown into molten steel according to the amount of molten steel passing through the immersion nozzle. The method disclosed in Patent Document 2 is a method in which a gas is blown into molten steel while an alternating current or a direct current is passed between a porous refractory for gas blowing provided on the inner wall of the immersion nozzle and the molten steel. It is.

  In these methods, the inclusion of the inclusions on the inner surface of the immersion nozzle is prevented by blowing an inert gas from the inner surface of the immersion nozzle into the molten steel. Moreover, in patent document 2, when energizing between the molten steel of the porous refractory for gas blowing, since the electromagnetic force will generate | occur | produce in molten steel and the diameter of the bubble produced | generated by this electromagnetic force will be decided, porous pore diameter The diameter of the generated bubbles does not increase even if the flow increases with the passage of time, and there are few bubble defects trapped by the solidified shell in the mold, and it is said that surface defects and the like are unlikely to occur in the product. .

  As described above, in any of the above methods, it is essential to blow inert gas from an immersion nozzle or the like, but when the amount of inert gas blown is insufficient, the inner surface of the immersion nozzle or the like in the molten steel There is a problem that adhesion of inclusions cannot be sufficiently suppressed.

  On the other hand, if the amount of inert gas blown is excessive, bubbles in the inert gas are trapped by the solidified shell in the mold, and bubble-type defects are generated in the surface layer of the slab. There is a problem that surface defects occur in the product.

  Moreover, in the method disclosed in Patent Document 2, since a 100 A or 200 A direct current or alternating current is continuously passed between the porous refractory for gas blowing and the molten steel, the current density increases, As a result, the electrical and thermal loads on the brittle porous refractory are larger than those of a normal dense refractory, and there is a problem that it cannot withstand long-time casting.

  In the continuous casting method for supplying molten steel from a tundish into a mold using an immersion nozzle, the present inventors have disclosed that the immersion nozzle body is made of an electrically conductive refractory. The continuous casting method of steel which enables prevention of obstruction | occlusion of an immersion nozzle inner hole by sending an electric current to the molten steel which passes the inner hole of an immersion nozzle through this, and suppressing adhesion of the inclusion to the inner surface of an immersion nozzle Disclosed.

  The method disclosed in Patent Document 3 and Patent Document 4 is a method for supplying molten steel in a tundish to a mold while energizing between the inner surface of the immersion nozzle and the molten steel passing through the interior of the immersion nozzle. Although it is similar to the method disclosed in Document 2, the method for preventing the adhesion of inclusions to the inner surface of the immersion nozzle and its idea are different.

  That is, in the method disclosed in Patent Document 2, the adhesion of inclusions to the inner surface of the immersion nozzle is realized by preventing the expansion of bubbles of the inert gas by using electromagnetic force. On the other hand, the methods disclosed in Patent Document 3 and Patent Document 4 are different from the above, in which the oxide accumulated near the interface between the molten steel and the immersion nozzle is polarized by energization, the interfacial tension changes, and the generation of the oxide By suppressing the generation of the source, the adhesion of inclusions to the inner surface of the immersion nozzle is suppressed.

  In addition, when a potential difference is applied between the immersion nozzle and the molten steel and a direct current is applied, the effect of preventing the immersion nozzle inner hole from being blocked is further stabilized by using the immersion nozzle side as a negative electrode. This is due to the difference in the immersion nozzle inner hole blocking prevention mechanism between the case where the immersion nozzle is on the negative electrode side and the case on the positive electrode side.

  The difference in the immersion nozzle inner hole blocking prevention mechanism between the case where the immersion nozzle is on the negative electrode side and the case where it is on the positive electrode side is considered as follows.

When the immersion nozzle is on the negative electrode side, the melting rate of the refractory is reduced and the elution of cations such as Al ³⁺ is suppressed, so the amount of Al ₂ O ₃ produced in the molten steel near the inner surface of the immersion nozzle is reduced. Decrease. Furthermore, since the decrease in the interfacial tension between the molten steel and the inclusions near the inner surface of the immersion nozzle due to the elution component from the refractory is also suppressed, the force due to the interfacial tension gradient acting on the inclusions in the steel decreases, and the steel Adsorption of inclusions on the immersion nozzle is also suppressed.

  Here, the interfacial tension gradient means the gradient of the interfacial tension between the molten steel and the inclusions in the direction from the molten steel to the immersion nozzle. When the absolute value of this value decreases, the inclusion particles are moved to the refractory side. The force attracted to or the speed of the steel is reduced, and the amount of inclusions in the steel on the immersion nozzle is reduced.

In contrast, when the immersion nozzle is on the positive electrode side, elution of cations in the refractory composition is promoted, resulting in an increase in the refractory erosion rate and the erosion rate exceeding the inclusion deposition rate. Apparently, the frequency of blockage of the inner diameter of the immersion nozzle is reduced. However, contrary to the case of the negative electrode described above, the amount of Al ₂ O ₃ generated increases due to the increase in cation elution, so that the tendency of adhesion of inclusions is also increased. Therefore, when the molten steel in the immersion nozzle has a low throughput (passage flow rate), the refractory has a low erosion rate, or the inclusion has a high inclusion rate, such as a high inclusion concentration in the steel. Below, the frequency of blockage of the inner diameter of the immersion nozzle may increase.

JP-A-4-319055 JP-A-6-182513 Japanese Patent No. 4089556 JP 2004-243385 A

Kaneko and two others, “(267) Immersion nozzle clogging mechanism in slab continuous casting”, Iron and Steel, Japan Iron and Steel Institute 66th (1980) No. 11, S868

  The technology for suppressing the adhesion of oxide to the inner surface of the immersion nozzle described in Patent Document 3 uses one electrode in the tundish as one electrode, and one immersion nozzle as the other electrode corresponding thereto, This is a method for obtaining an effect of suppressing the clogging of the inner hole of the immersion nozzle by applying a voltage having a waveform in which a positive voltage and a negative voltage appear alternately with a time difference between the other electrode. However, Patent Document 3 does not mention the correspondence to an apparatus having a plurality of immersion nozzles, such as a continuous casting machine of steel having a plurality of strands.

  In the technique described in Patent Document 4, when energizing between a plurality of immersion nozzles, one of the immersion nozzles is a positive electrode and the other immersion nozzle is a negative electrode. It has been difficult to uniformly obtain the effect of suppressing the adhesion of oxide to the inner surface.

  However, in actual steel continuous casting machines, it is common to have two or more strands. In the continuous casting machine of steel having a plurality of strands, in order to obtain the effect of suppressing the adhesion of oxide to the inner surface of the immersion nozzle during casting, the conventional method uses one immersion electrode provided as many strands as one electrode, On the other hand, it is necessary to install the same number of power supply devices and the other electrode (counter electrode) in the tundish.

  This is because when a single power supply is used for a plurality of immersion nozzles as one electrode and only one counter electrode is arranged in the tundish, an electric circuit formed corresponding to each immersion nozzle Because of the difference in the electrical resistance value, there is a significant difference in the energization current value of each electrical circuit, and this significant difference may cause a difference in the effect of suppressing the adhesion of oxide to the inner surface of the immersion nozzle for each strand. is there.

  This conventional method has a problem that the load for setting the counter electrode in the tundish is very large, and the cost of the refractory for forming the counter electrode increases.

  The present invention has been made in view of the above-described problems, and its object is to provide an apparatus having a simple structure for suppressing the adhesion of oxide to the inner surface of an immersion nozzle during continuous casting of steel using a plurality of strands. It is providing the manufacturing method of the continuous cast slab which can be obtained equally and stably by each strand using.

  In order to solve the above-mentioned problems, the present inventors have arranged one refractory as a counter electrode (hereinafter referred to as “counter electrode refractory”) in the tundish, and from this counter refractory to the immersion nozzle holding device of each strand. We examined the case where a parallel electric circuit was constructed in which an energized cable was connected and connected to the counter refractory via a power supply device.

  As a result, when only one power supply device is arranged for a plurality of electric circuits constituting the parallel electric circuit, the electric resistance of each electric circuit is not necessarily equal, so that the electric circuit having a small electric resistance is obtained. It has been found that power is given priority. In this case, the present inventors have found that the phenomenon that the effect of suppressing the adhesion of oxides to the inner surface of each immersion nozzle is different due to the difference in the energization state for each electric circuit.

  As a result of further studies on this problem, the present inventors have decided to control the energization current value for each electric circuit by arranging a power supply device in each electric circuit constituting the parallel electric circuit. Pay attention.

  However, as a result of studying from this point of view, the present inventors, when energizing a parallel electric circuit having a plurality of power supplies, if a different power supply voltage is set for each electric circuit, it acts on a circuit having a large voltage. It has been found that a phenomenon occurs in which the voltage to be generated hinders the energization of a circuit having a small voltage. For this reason, when a power supply voltage differs for every electric circuit in a parallel electric circuit, it is not easy to supply a predetermined electric current to each electric circuit.

  For this reason, the present inventors have conceived that the power supply voltage of each electric circuit is equalized as a method of supplying a predetermined current without affecting the energization of another electric circuit by a specific electric circuit, and As a result of the investigation, the following knowledge was obtained.

  It is possible to establish stable energization conditions by sharing one counter electrode refractory in the tundish with the electric circuits provided in each of the plurality of strands and arranging the power supply device in the electric circuit of each strand. It was found that the effect of suppressing the adhesion of oxide to the inner surface of the immersion nozzle was further improved. Furthermore, since only one counter refractory can be provided, the cost of the counter refractory can be reduced and the setting work load of the counter refractory can be reduced.

  In addition, in the electrical circuit of each strand, the inventors, when energized so that the polarity of the immersion nozzle is alternately switched, with respect to the time period in which each immersion nozzle is a positive electrode and a negative electrode, there is a difference for each electrical circuit or Even if the time period is the same, if the timing (phase) at which the positive electrode and the negative electrode are switched differs for each electric circuit, the energization in each electric circuit interferes with the energization state of the other electric circuit, It has been found that it is difficult to obtain a stable energized state in each of the electric circuits of all the strands.

  To solve this problem, the time period and the phase for switching the polarity of each immersion nozzle are made the same (synchronized), so that even if the electrical circuits of a plurality of strands are energized simultaneously, It has been found that interference can be suppressed and a stable energized state can be obtained in each of the electrical circuits of all strands.

  This invention is made | formed based on the said knowledge, and makes the summary the manufacturing method of the following continuous cast slab. That is, a continuous casting slab manufacturing method used in a continuous casting machine having a plurality of strands, in which molten steel in a tundish is introduced into dipping nozzles corresponding to the respective strands, and is supplied to the mold of each strand through each dipping nozzle. In each, each immersion nozzle is used as one electrode, and a common electrode is immersed in the molten steel in the tundish as a counter electrode of each of these electrodes to form an electric circuit for each strand, and a power source is arranged in each electric circuit. Then, energization of a pulse waveform in which the current value is 10 to 300 A and the period is 6 to 20 ms and the voltage is alternately switched from each power source to each electric circuit is performed with the same period, phase, and voltage. And the period when the said immersion nozzle becomes a negative electrode in 1 period of the said pulse waveform is made longer than the period when it becomes a positive electrode. A method for producing a continuously cast slab that.

  In the following description, “mass%” representing the component composition of steel is simply expressed as “%”.

  By using the continuous casting slab manufacturing method of the present invention, when continuously casting steel using a plurality of strands, the effect of suppressing the adhesion of oxides to the inner surface of the immersion nozzle can be reduced by using an apparatus with a simple configuration. It can be obtained equally and stably. As a result, it is possible to achieve continuous casting operation stabilization and obtain a continuous cast slab having good surface and internal quality.

It is the schematic which shows the principal part of the continuous casting apparatus which can apply the manufacturing method of the continuous cast slab of this invention.

  As described above, the method for producing a continuous cast slab according to the present invention is used in a continuous casting machine having a plurality of strands. The molten steel in the tundish is introduced into immersion nozzles corresponding to the respective strands, and each through the immersion nozzles. In the manufacturing method of continuous cast slabs to be supplied to the mold of each strand, each immersion nozzle is used as one electrode, and one shared electrode is immersed in the molten steel in the tundish as a counter electrode of each electrode. An electric circuit is configured, a power source is arranged in each electric circuit, a current waveform of 10 to 300 A, a period of 6 to 20 ms, and a positive and negative voltage waveform are alternately switched from each power source to each electric circuit. Energization is performed with the same period, phase, and voltage, and the period during which the immersion nozzle is negative in one period of the pulse waveform is positive. It is a method for longer than the period to be. The contents of the present invention will be described below.

  FIG. 1 is a schematic view showing a main part of a continuous casting apparatus to which the method for producing a continuous cast slab of the present invention can be applied. An immersion nozzle 2 is provided on the bottom surface of the tundish 1 via a sliding plate 3 one by one corresponding to a plurality of strands (not shown). The sliding plate 3 is composed of three layers of upper and lower fixed plates having holes through which molten steel passes and a central sliding plate, and the flow rate of the molten steel is adjusted by moving the sliding plate. The molten steel 6 accommodated in the tundish 1 is cooled by spray water sprayed from a mold 4 and a secondary cooling spray nozzle (not shown) below the mold 4 through an immersion nozzle 2 to form a solidified shell and continuously cast. It becomes a piece.

  Further, one power supply device 5 is arranged corresponding to each immersion nozzle 2. One end of a cable 10 a and a cable 10 b is connected to each power supply device 5. The other end of the cable 10 a is connected to an electrode 8 provided on the side surface of each immersion nozzle 2. The other end of the cable 10 b is connected to an electrode terminal 9 provided at one end of a counter electrode 7 made of a rod-like refractory disposed in the tundish 1. The other end of the counter electrode 7 is immersed in the molten steel 6. Thus, a parallel electric circuit is comprised by the some immersion nozzle 2 which is one electrode, and the one counter electrode 7 corresponding to this.

  As shown in FIG. 1, in the tundish and immersion nozzle peripheral device used in the method for producing a continuous cast slab according to the present invention, each electric circuit constituting the parallel electric circuit shares one counter electrode 7. Compared with the case where the device is provided, the apparatus can be simplified in configuration, and the cost of the counter electrode 7 and the setting work load can be reduced.

  In the production of a continuous cast slab, the electrical circuit is energized in a waveform in which the positive and negative voltages are alternately switched under the control of the power supply device 5 with the same period, phase, and voltage. Thereby, it becomes possible to supply a predetermined current to each electric circuit, and the effect of suppressing the adhesion of oxide to the inner surface of the immersion nozzle 2 can be obtained equally in each strand.

  The energization condition is a pulse waveform having a current value of 10 to 300 A and a period of 6 to 20 ms. Here, the pulse in the energization waveform refers to a rectangular wave.

  The technique for suppressing oxide adhesion to the inner surface of an immersion nozzle by the method for producing a continuous cast slab of the present invention can be applied to the production of carbon steel and alloy steel in general, and there are no restrictions on the upper limit value and lower limit value of the component composition. Absent. However, the electrical current condition of the electrical circuit of each strand is that the oxide accumulated near the interface between the molten metal and the immersion nozzle is polarized, the interfacial tension changes, and the generation of the oxide generation source is suppressed. It is necessary to set the conditions to exert the effect of suppressing the adhesion of oxide to the surface.

  For this reason, the energization current value is in the range of 10 to 300A. When the energization current value is less than 10 A, the interfacial tension lowering effect cannot be sufficiently obtained, and it may be difficult to exert the stable effect of suppressing the adhesion of oxide to the inner surface of the immersion nozzle. When the current value exceeds 300 A, the current density is large, the electrical and thermal load on the refractory that constitutes the immersion nozzle is large, and the power supply equipment that supplies power, the power supply equipment such as cable wires, etc. are large-scale In addition, since the spark is likely to be generated at the electrode joint portion, the operation is difficult. The range of the energization current value is preferably 50 to 200A, and more preferably 100 to 200A.

  The pulse has a period in the range of 6 to 20 ms. In the case of short-period pulses with a period of less than 6 ms and long-period pulses with a period of more than 20 ms, the time during which the immersion nozzle body is positive or negative in one cycle of the pulse is too short or too large, forming a unique immersion nozzle for pulse energization Therefore, the effect of suppressing the adhesion of oxide due to the change in polarity of the refractory is not obtained.

  The difference between the time when the immersion nozzle body is the negative electrode and the time when it is the positive electrode in one cycle of the pulse (the value obtained by subtracting the time when it is the negative electrode from the time when it is the negative electrode) may be greater than 0.20 ms and less than 1.40 ms. preferable. According to the results studied by the present inventors, it has been found that if the pulse period is in the range of 6 to 20 ms and the time difference is in this range, a good oxide adhesion suppressing effect can be obtained.

  The method for producing a continuous cast slab of the present invention can be applied to the production of carbon steel and alloy steel in general, and there is no restriction on the upper limit value and the lower limit value of the component composition as described above. For example, C: 0.10 to 1.10%, Si: 0.10 to 0.50%, Mn: 0.50 to 1.20% as steel types suitable for the continuous casting slab manufacturing method of the present invention. , P: 0.05% or less, S: 0.060% or less of carbon steel, C: 0.10 to 1.10%, Si: 0.10 to 2.00%, Mn: 0.50 to 1 20%, P: 0.05% or less, S: 0.050% or less, Al: 0.01 to 0.10%, N: 0.005 to 0.03%, with respect to Cr, Ni and Mo Is an optional additive component, and includes alloy steels with Cr: 1.50% or less, Mo: 1.0% or less, and Ni: 2.0% or less.

  In order to confirm the effect of the manufacturing method of the continuous cast slab of the present invention, the following experiment was performed and the result was evaluated.

1. Experimental conditions Using the continuous casting apparatus shown in FIG.

  The steel type used for the casting experiment was a carbon steel of C: 0.56%, Si: 0.20%, Mn: 0.80%, P: 0.020%, S: 0.005% as molten steel. . The continuous casting amount of the molten steel in each strand was 100 tons. The dimensions of the slab were 400 to 470 mm in width and 300 to 340 mm in thickness.

  The casting speed and energization conditions (energization voltage, energization current value, and positive / negative electrode switching cycle) during the casting experiment were as shown in Table 1. The energization waveform was a rectangular wave pulse, and each electric circuit was energized using the same power source with the same pulse period (positive / negative electrode switching period), phase, and voltage. In Table 1, one of the two strands was described as a first strand and the other as a second strand.

  Experiment numbers 1 and 2 are comparative examples in which no electric current was applied to the electric circuit. Experiment No. 3 is a comparative example in which the energization voltage differs between the first strand and the second strand. Experiment No. 4 is a comparative example in which the positive / negative electrode switching cycle is different between the first strand and the second strand. Experiment numbers 5 and 6 are examples of the present invention that both satisfy the provisions of the present invention. Experiment numbers 7 and 8 are comparative examples in which the positive / negative electrode switching period does not satisfy the provisions of the present invention.

2. Evaluation Items Table 1 shows the evaluation items and the results together with the experimental conditions. The evaluation items were “the thickness of the deposit on the inner surface of the nozzle after use”, “the degree of progress of the sliding plate opening”, and “the fluctuation range of the molten metal surface in the mold”.

  “Post-use nozzle inner surface deposit thickness” and “sliding plate opening degree progress” are evaluation indexes of the effect of suppressing the adhesion of oxide to the inner surface of the immersion nozzle.

  The “thickness on the inner surface of the nozzle after use” is an average value of the thickness of the oxide adhering to the inner surface of the immersion nozzle, which was measured from four locations in the longitudinal direction by vertically cutting the immersion nozzle after the casting experiment. is there. The measurement positions were 50 mm below the slag line, the slag line part, and 100 mm and 200 mm above the slag line.

  The “sliding plate opening degree of progress” is an absolute value of a change value (difference) between the initial opening degree and the final opening degree of the sliding plate during continuous casting of 100 tons of molten steel in each strand. The opening degree of the sliding plate means the sliding stroke length of the sliding plate of the sliding plate shown in FIG.

  When there is no blockage of the immersion nozzle inner hole, the opening degree of the sliding plate is stable, and the degree of progress of the sliding plate opening degree is almost zero. On the contrary, when the clogging of the immersion nozzle bore occurs, the sliding plate opening at the end of continuous casting is larger than the initial opening, so the sliding plate opening compared to the case without clogging Progression becomes large.

  “Valve surface fluctuation width in mold” is the fluctuation width of the molten steel surface in the mold at each strand from the start to the end of continuous casting. This is an index indicating the possibility of occurrence of.

  The molten steel surface in the mold is controlled so as to be maintained at a fixed position by opening and closing the sliding plate. However, when an oxide adheres to the inner surface of the immersion nozzle during casting and the deposit is peeled off, the molten steel passage cross-sectional area in the immersion nozzle instantaneously increases, and the flow rate of molten steel supplied to the mold increases. To do. At this time, if the opening / closing control of the sliding plate is slightly delayed, the molten steel surface in the mold greatly fluctuates. When the molten metal surface fluctuation width in the mold is large, there is a high possibility that the mold powder put on the molten steel in the mold is wound in an unhatched state and a slab surface subcutaneous defect is generated. It is generally known that the smaller the molten steel inner surface fluctuation width, the better the surface quality of the resulting ingot.

3. Experimental results As shown in Table 1, in the experiment numbers 1 and 2 which are comparative examples in which the electric circuit was not energized, the “thickness on the inner surface of the nozzle after use” was 5 to 6 mm. It was a large numerical value as compared with the Example.

  On the other hand, in Experiment Nos. 5 and 6 that satisfy the requirements of the present invention, the “post-use nozzle inner surface deposit thickness” was as extremely small as 1 to 2 mm, and a significant oxide adhesion suppressing effect was recognized. Also, the opening of the sliding plate did not change. Furthermore, the fluctuation range of the molten metal surface in the mold was also ± 1 mm, and almost no variation of the molten metal surface was observed, and the same effect of suppressing the adhesion of oxide to the inner surface of the immersion nozzle was obtained for all of the plurality of strands.

  Regarding the significant difference when the energization conditions are different between the first strand and the second strand, the experiment number 3 with different energization voltages and the experiment number 4 with different positive / negative electrode switching cycles In both cases, the “thickness of deposit on the inner surface of the nozzle after use” was as large as 3 mm and 4 mm, the sliding plate opening was advanced by 1 mm and 2 mm, and a variation of the hot water level in the mold of 3 mm at maximum was observed.

  This is presumed to be the effect of the large voltage circuit interfering with the energization of the small voltage circuit in the case of Experiment No. 3 due to the difference in the voltages applied to the electrical circuits. This is presumably due to the influence of unstable energization current due to mutual interference in the parallel electric circuit due to the difference between the positive / negative electrode switching periods in the electric circuit.

  On the other hand, in Experiment No. 7, the positive / negative electrode switching cycle was too short, and a sufficient interfacial tension reduction effect at the interface between the immersion nozzle refractory and the molten steel was not obtained. Therefore, the “thickness on the nozzle inner surface after use” was as large as 4 mm and the “in-mold molten metal surface fluctuation width” was as large as ± 4 mm, and a sufficient effect of suppressing the adhesion of oxide to the inner surface of the immersion nozzle could not be obtained.

  In Experiment No. 8, it was not possible to obtain the expected effect of suppressing the adhesion of oxide to the inner surface of the immersion nozzle. This is because the positive electrode / negative electrode switching cycle is excessive, and the time during which the immersion nozzle is the positive electrode is long in one cycle of the positive electrode / negative electrode switching cycle, so that the amount of oxide attached to the inner surface of the immersion nozzle increases. It is estimated that

  By using the continuous casting slab manufacturing method of the present invention, it is possible to obtain the same effect of suppressing the adhesion of oxide to the inner surface of the immersion nozzle in each strand during continuous casting of steel using a plurality of strands. It is. As a result, it is possible to achieve continuous casting operation stabilization and obtain a continuous cast slab having good surface and internal quality.

  The present invention solves the problem that the effect of suppressing the clogging of the immersion nozzle in each strand that could not be solved by the prior art is not equivalent, and is very valuable industrially.

1: tundish, 2: immersion nozzle, 3: sliding plate, 4: mold,
5: Power supply device, 6: Molten steel, 7: Counter electrode, 8: Electrode, 9: Electrode terminal, 10a: Cable, 10b: Cable

Claims (1)

In a continuous casting slab manufacturing method used in a continuous casting machine having a plurality of strands, introducing molten steel in a tundish into dipping nozzles corresponding to the respective strands, and supplying each of the strands to a mold of each strand through each dipping nozzle,
Each immersion nozzle is set as one electrode, and one shared electrode is immersed in the molten steel in the tundish as a counter electrode of each electrode to constitute an electric circuit for each strand, and a power source is arranged in each electric circuit,
A current of 10 to 300 A and a period of 6 to 20 ms from each power source to each electric circuit is applied with a pulse waveform in which the voltage is alternately switched between positive and negative with the same period, phase and voltage.
And the manufacturing method of the continuous cast slab characterized by making the period when the said immersion nozzle becomes a negative electrode in 1 period of the said pulse waveform longer than the period when it becomes a positive electrode.

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