JP2003080352A - Continuous cast slab manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cast slab with the solute element concentration of a cast slab surface layer part constant by adequately adjusting the solute element concentration of the cast slab surface layer part without generation of defects in the cast slab or degradation of the productivity attributable to reduction of the temperature of the molten steel inside a mold. SOLUTION: In a continuous cast slab manufacturing method in which the molten steel is poured in a molten steel pool within the DC magnetic field zone or above the DC magnetic field zone by using an immersion nozzle in an upper molten steel pool while applying the DC magnetic field zone to the entire width of the cast slab in the direction across the thickness of the cast slab at the position below the molten steel level in a continuous casting mold by the predetermined distance in the casting direction, the solute element concentration of the molten steel in the upper pool is increased by adding the predetermined solute element in the upper molten steel pool, and the solute element concentration of the cast slab surface layer is adjusted thereby, a wire containing the solute element is fed into the molten steel while the wire is heated and melted by a heating means above the mold when adding the predetermined solute element to the molten steel in the upper pool.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a continuously cast slab having a gradient composition in which the concentration of a specific solute element in the surface layer portion is higher than that in the inside of the slab.

[0002]

2. Description of the Related Art Heretofore, various methods have been proposed for producing a slab having a different composition in the surface layer portion and in the interior thereof by continuous casting. For example, in Japanese Patent Laid-Open No. 7-51801, molten steel is vertically injected into a mold for continuous casting,
A direct current magnetic field is applied over the entire width in the mold at a position above the molten steel injection position to decelerate the upward flow of the molten steel, and an alloy element different from the molten steel component is added to the molten steel above the position where the direct current magnetic field is applied. A method for producing a multi-layered steel sheet is described, which comprises adding a wire containing the molten steel and forming the surface layer of the alloy steel on the surface of the billet by using the molten steel in the upper part as a molten alloy steel by the floating stirring of the injected gas.

Further, in Japanese Unexamined Patent Publication No. 8-257692, a DC magnetic field is applied over a full width of the mold at a certain distance below the meniscus to form a braking area, and an immersion nozzle having nozzle discharge holes above and below the meniscus is used. By injecting molten steel with a constant composition and then continuously supplying the alloying elements to the molten steel pool above the braking area using a wire, stirring by the molten steel injection flow is performed, so that the alloying element concentration in the surface layer is uniform. A method of making a multi-layer slab is disclosed.

[0004]

However, in these methods, since the heat content of the molten steel in the mold is deprived by adding the wire, the temperature of the molten steel in the mold is lowered and There was a problem that inclusions and powder defects inside the mold increased due to skinning and the like.
Further, when the temperature of the molten steel inside the mold is lowered and the difference from the melting temperature (melting point) becomes close to 0 ° C., casting becomes impossible, so that there remains a problem in that the amount of wire that can be added is limited. .

Therefore, in Japanese Patent No. 3020127, it was proposed to add the wire to be added to the molten steel while heating it by electric resistance heating or high frequency heating between the supply pinch roll and the molten steel. However, the inventor conducted detailed investigations on the above method by experiments and found that even by this method, the occurrence of slab defects due to local solidification of molten steel in the mold cannot be completely prevented. Became.

[0006] The present invention advantageously solves the above-mentioned problems. Solutes in the surface layer of the cast slab are generated without inducing slab defects or lowering the productivity due to the decrease of the molten steel temperature inside the mold. An object of the present invention is to propose an advantageous method for producing a continuously cast slab capable of appropriately adjusting the element concentrations.

[0007]

Means for Solving the Problems That is, the gist of the present invention is as follows. 1. During continuous casting of molten steel, a DC magnetic field band was applied across the entire width of the cast piece in a direction that traverses the thickness of the cast piece at a position below a certain distance in the casting direction from the level of the molten metal in the continuous casting mold. While injecting molten steel into the molten steel pool in or above the DC magnetic field zone using a dipping nozzle, by adding a specific solute element to the molten steel in the DC magnetic field zone or above the DC magnetic field zone, In the method for producing a continuously cast slab, which comprises increasing the concentration of the solute element in the molten steel in the upper pool and adjusting the concentration of the solute element in the surface layer of the slab, a specific solute element is added to the molten steel in the upper pool. At that time, the wire containing the solute element is supplied into the molten steel in a state of being heated and melted by a heating means above the mold, and then supplied to the molten steel.

2. The method for producing a continuously cast slab according to the above item 1, wherein the wire is heated and melted by a heating means to form a molten metal, and the molten metal is injected into the molten steel in the mold through a heat-insulated path.

3. The method for producing a continuously cast slab according to the above 1 or 2, wherein the heating means is high frequency induction heating.

4. 4. The method for producing a continuously cast slab according to the above 3, wherein the heat-retained path is curved downward above the mold.

5. The method for producing a continuously cast slab according to any one of 3 to 4 above, wherein the wire diameter is 3 to 20 mm and the frequency in high frequency induction heating is 30 to 50 kHz.

6. 3. The method for producing a continuously cast slab according to the above 1 or 2, wherein the heating means is arc heating.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below with reference to the drawings. FIG. 1 schematically shows an example of how to add a solute element into the mold according to the present invention. In the figure, numeral 1 is a wire reel, 2 is a high-frequency induction heating coil as a heating means, 3 is a magnetic shield material for protecting the surroundings, 4 is a molten metal introduction tube made of a refractory material, and 5 is embedded therein. It is a heating wire, and a molten metal supply path is formed by these 4 and 5. 6 is a wire (a nickel wire in this example), 6'is molten nickel after heating and melting, and 7 is molten steel. In addition to the above-mentioned high frequency induction heating, arc heating can be used as the heating means. When supplying the wire into the molten steel in the mold, first, the wire 6 is fed from the wire reel 1 toward the high frequency induction heating coil 2. Then, the wire 6 is heated and melted while passing through the high frequency induction heating coil 2 and then supplied into the molten steel 7.

However, the molten nickel 6'after being melted by heating may be left in a semi-solidified state by heat removal from the surroundings and may be clogged. Therefore, it is desirable to inject the molten nickel 6'into the molten steel 7 after melting, through a path kept warm by electric heating or the like. The wire 6 may be supplied to any path up to the high frequency induction heating coil. However, since it is desired that the wire 6 be quickly supplied into the molten steel 7 after being heated and melted, the molten nickel 6 Advantageously, the'path is curved downwards above the mold.

According to the present invention, the following advantages can be expected by heating and melting the wire and adding it to the molten steel. First,
By using the wire as the solute element to be added, it becomes possible to continuously add the solute component into the molten steel at a constant rate. Further, since the wire is heated and melted and supplied in a molten state, it is possible to prevent local solidification of the molten steel. For example, the above-mentioned JP-A-7-51801 and JP-A-8-2576.
In the technique of Japanese Patent No. 92, the wire is added to the molten steel without being heated, so that the surrounding molten steel is inevitably cooled and solidified. Also, Patent No. 3020 that heats and adds the wire
The technology described in No. 127 also has a problem that the surrounding molten steel solidifies. This is because even if the wire is heated and added, the molten steel solidifies because the latent heat of melting is taken from the surrounding molten steel when the wire melts in the molten steel. However, according to the present invention, since the wire is melted in advance and added to the molten steel in the form of droplets or liquid flow, the latent heat of melting as described above is not taken from the surrounding molten steel. Moreover, since it is in the liquid phase, it is quickly added to the molten steel and then diffused into the molten steel, which also has the effect of improving the uniformity of the distribution of the concentration of the solute element in the molten steel pool in the mold.

For the above reason, in the present invention, the wire is melted by heating and supplied into the molten steel. However, when the melting point of the wire is low, the solute element after melting reaches the molten steel temperature. Sensible heat will be taken away from the surrounding molten steel,
This may lead to local solidification of molten steel. Therefore, it is more preferable that the heating temperature of the wire is equal to or higher than its melting point and about 1400 ° C. or higher. By heating in this way, it becomes possible to prevent local solidification of molten steel as much as possible.

Next, the proper frequency when high frequency induction heating was used as the heating means was investigated in relation to the melting rate of the wire. As a result, it was found that if the frequency is lowered too much, the skin depth becomes deeper, and the magnetic fields interfere (cancel each other) and transmit, resulting in a decrease in heating efficiency. Here, according to the experiments by the inventors, it was found that the lower limit of the frequency was 30 kHz, and the wire could not be melted at the frequency lower than that. On the other hand, from the viewpoint of melting efficiency, the upper limit of the frequency is not particularly limited, but generally, when the frequency becomes higher, the power supply equipment cost rapidly increases, and there is a problem that it interferes with the signal of the eddy current sensor used as the melt level meter. Occurs. Therefore, it is desirable to set the upper limit of the frequency to about 50kHz in order to avoid interference with the eddy current sensor.

If the wire diameter is too small, it is necessary to feed it at a high speed in order to inject the required amount, and the residence time in the heating zone of the high frequency coil becomes short, so there is a possibility that it cannot be sufficiently melted. . On the other hand, if the wire diameter is too large, it cannot be heated to the center by the high-frequency coil, and thus sufficient heating and melting cannot be expected. Therefore, the inventors
We also conducted experiments on this point, and in order to supply a sufficient amount while heating and melting the wire, the wire diameter was 3 to 20.
It has been found that setting a value of about mm is effective.

Regarding the heating position of the wire, if the transportation distance is too long after the wire is heated and melted, a temperature drop occurs between them. Therefore, it is desirable that the wire heating position is as close to the mold as possible, but installing the high-frequency coil above the mold not only adversely affects the cooling of the high-frequency induction heating coil due to radiation from molten steel, but also The interference with the eddy current sensor provided for detecting the molten steel molten metal level is increased, which is not desirable. Also, the heating means is installed above the mold in a state of being separated from the mold,
It is practically difficult because it requires a large space distance from the mold to the tundish. Therefore, as shown in FIG. 1, a heating means is installed between the wire reel and the upper part of the mold, and the wire is heated and melted by this heating means, and then the molten steel is passed through a path kept warm by electric heating or the like. Injection is preferred. And in order to install such a heating device in the limited space of the upper part of the mold and the tundish,
It is advantageous to curve the above-described path downwardly and vertically above the mold.

Further, the inventors have also investigated a suitable molten steel temperature when supplying such a wire.
Figure 2 shows the results of an examination of the relationship between the wire feed temperature and the drop in molten steel temperature in the mold when 27 kg / t of nickel is fed into the molten steel by wire feeding. As is clear from the figure, the molten steel temperature drops by 50 ° C or more without preheating. Although the temperature drop can be reduced by preheating, the molten steel temperature will drop by nearly 20 ° C to compensate for the heat of fusion even if heated to near the melting point of 1450 ° C.

Therefore, conventionally, in order to prevent the molten steel from solidifying due to the addition of the wire, it has been necessary to allow the temperature of the molten steel to rise and to raise the temperature of the molten steel to be injected into the mold higher than usual. . Usually, in continuous casting of steel,
Since there is a molten steel temperature drop from the tundish to the mold, anticipate this, the molten steel superheat degree in the tundish (molten steel temperature in the tundish-solidification temperature of molten steel) is 20 to 70 ° C.
It is often operated as a degree, but when adding the wire according to the above-mentioned conventional technique, in addition to this, 20 ~
It was necessary to raise the temperature by about 50 ° C. This is
Not only does it increase the load on the converter, which is a steelmaking furnace, the RH degassing device, which is a secondary refining furnace, and the ladle refining furnace such as LF,
This caused a problem of accelerating the wear of the refractory material of the ladle. Furthermore, in the mold, the temperature of the molten steel is high except in the area in contact with the wire, which delays the growth of the solidified shell in the area in contact with the inner surface of the mold, which causes breakout, deformation of the slab, and bulging. There was a problem that the occurrence rate of operation troubles and quality troubles due to the increase. However, according to the present invention, since it is not necessary to particularly raise the molten steel superheat degree in the tundish as compared with the normal operation, it is effective to increase the refining load and the occurrence of casting troubles and quality troubles as described above. Can be prevented.

In practicing the present invention, it is preferable to use a continuous casting machine as shown in FIG. 3 having an immersion nozzle having a single lower discharge hole and two upper discharge holes.
In the figure, numeral 8 is a mold, numeral 9 is a dipping nozzle, and numeral 10 is a magnetic pole. By this magnetic pole 10, a DC magnetic field band can be applied over the entire width of the slab in the thickness direction of casting. And
11 indicates the height center of the magnetic field. Further, 12 is a lower discharge hole of the immersion nozzle 9, 13a and 13b are upper discharge holes of the immersion nozzle 9, 14 is a jet from the lower discharge hole, and 15a and 15b are jets from the upper discharge holes 13a and 13b. The reverse flow from the lower pool to the upper pool in the DC magnetic field band is shown at 16. 17 is a solidified shell. In the figure, w is the width of the mold, θ and θ ′ are the angles of the discharge holes 12 and 13 at the bottom and top of the immersion nozzle 9, respectively (the downward angle with the horizontal direction at 0), and h is the immersion nozzle. The distance from the lower end of the discharge hole to the height center of the magnetic pole, h'is the distance from the upper discharge hole to the height center of the magnetic pole.

As shown in FIG. 3, the molten steel jet 14 supplied from the immersion nozzle 9 once flows into the lower pool of the magnetic field zone, but the molten steel supply speed to the upper pool is solidified and consumed in the upper pool. By lowering the speed below the above, and by making the shortage in the upper pool of the molten steel once flowing into the lower pool naturally flow back to the upper pool again,
It does not cause problems with the control of the molten steel feed rate.

It should be noted that it is important to arrange the lower discharge hole at an appropriate position in order to easily cause a backflow around the molten steel jet supplied to the lower pool. Then, as a result of various studies on this point, it was found that it is preferable to satisfy the following relations with respect to the nozzle position, the ejection angle, and the magnetic field application position. h <(1/2) ・ w ・ tan θ --- (1) 0 <h ≤ 0.3 --- (2) where θ: downward angle (°) of immersion nozzle discharge hole w: width direction of mold Length (m) h: Distance from the lower end of the immersion nozzle discharge hole to the height center of the magnetic pole (m)

The reason why the equation (1) is necessary is that if this condition is not satisfied, the jet collides with the wall surfaces at both ends before sufficiently penetrating the magnetic field zone, and the backflow from the lower pool is sufficiently generated. Because it cannot be caused. The reason why equation (2) is necessary is that if this condition is not satisfied, the jet flow will diffuse before penetrating the magnetic field band, and it will not be possible to sufficiently induce backflow.

On the other hand, it is necessary to prevent the molten steel flow from the upper discharge hole from flowing out to the lower pool. For that purpose, it is desirable to satisfy the following expression (3). Further, in order to sufficiently draw the molten steel flowing from the lower pool, it is desirable to satisfy the following expression (4). h ′> (1/2) ・ w ・ tan θ ′ --- (3) 0 <h ≦ 0.3 --- (4) where θ ′: downward angle (°) of upper discharge hole w: mold Length (m) h ': Distance from the center of the upper discharge hole to the height center of the magnetic pole (m)

The molten steel feed rate from the upper discharge holes is determined by considering the variation of the molten steel feed ratio from the upper and lower discharge holes.
It should be set lower than the rate consumed by coagulation in the upper pool. However, if the molten steel supply rate is less than 0.3 times the molten steel consumption rate in the upper pool, even under the condition that Eq. (4) above is satisfied,
In some cases, the jet velocity may not be sufficient to draw in the molten steel supplied from the lower pool and the added solute element and mix them. Therefore, regarding the supply rate Q '(ton / min) of the molten steel supplied from the upper discharge hole and the consumption rate Q (ton / min) of the molten steel solidified in the upper molten steel pool, the relation of the following equation (5) is satisfied. It is preferable that 0.3 · Q ≦ Q ′ ≦ 0.9 · Q --- (5) Where, Q ′: Supply speed of molten steel supplied from the upper discharge hole (ton / min) Q: In the molten steel pool above the height center of the magnetic pole Rate of molten steel that solidifies and solidifies (ton / min)

Further, in order to make the solute concentration in the surface layer of the cast slab more uniform, it is preferable to add the heated and melted additive element to a position where it is easily drawn into the jet from the upper discharge hole.
Furthermore, as a result of detailed study on this point, it was found that it is more effective to add under the conditions satisfying the following relationships. 0 <z ≤ 0.6 --- (6) Here, z is the distance (m) from the solute element addition position to the height center of the magnetic pole. The simplest method is to extend the path kept warm by such means as immersing it in the molten steel.

When the operation is carried out under the conditions satisfying the above equations (1) to (6), a slab having a uniform concentration of solute elements in the surface layer of the slab can be produced with a high yield. Was determined.

Even in the case of a two-hole nozzle used in ordinary continuous casting, if the conditions (1) and (2) are satisfied, a desired local inflow site can be effectively generated. It is possible. Further, in order to further enhance the effect of locally forming the inflow portion and the effect of damping the nozzle jet flow, it is preferable to arrange the nozzle ejection holes above the magnetic pole center.

Here, if the strength of the applied magnetic field is too small, the braking effect by the magnetic field is weakened, and molten steel in the upper pool and the lower pool may be mixed. On the other hand, if it is too strong, it enters the upper pool. The influx of
Since more molten steel than required is supplied to the upper pool, as a result, molten steel in the upper pool may flow out at a site away from the inflow position. It is important to have an appropriate strength that does not cause the mixing of Al and the uniform dissolution of alloying elements, and it is usually preferable to set the strength to about 0.1 to 0.5 T.
Similarly, if the flow rate of Ar gas injected into the nozzle is too high, the flow of Ar gas into the upper pool becomes too strong,
It is desirable to set the Ar gas flow rate to 20 liters / min or less because foaming defects are likely to occur.

Further, with respect to the width (height direction) of the applied DC magnetic field band, if the width is too small, the braking effect is not sufficient, while if it is too large, the power supply capacity or coil size required to generate the magnetic field is large. Since the equipment cost increases, the width of the magnetic pole in the height direction is
It is preferable that the length is about 0.5 m.

[0033]

EXAMPLE A continuous cast slab was produced under the following conditions (adapted example of the present invention) using the continuous casting mold shown in FIG.・ Inner diameter of the mold Long side (w): 0.4 m, Short side: 0.11 m ・ Direct current magnetic field application position (distance from the molten metal level in the mold to the height center of the magnetic pole) A: 0.347 m Applied magnetic field strength: 0.3 T Magnetic pole height: 0.15 m ・ Immersion nozzle Nozzle inner diameter: 40 mm Upper discharge hole: 2 holes (hole size 10 × 10 mm) Discharge angle θ ′ = 0 ° (horizontal) Lower discharge hole: Single hole (hole size 28 mmφ) Discharge angle θ = 90 ° (vertically downward) ・ Lower discharge hole immersion depth (from mold surface level to lower discharge hole bottom): 0.34 m ・ Upper discharge hole immersion depth (mold level from melt surface to upper part) To the center of the discharge hole): 0.177 m ・ Distance h from the center of the lower discharge hole to the height of the magnetic pole h:
0.007 m ・ Distance h'from the center of upper discharge hole to the center of magnetic pole height h ':
0.170 m ・ Casting speed Vc: 1.6 m / min (Casting amount: 0.49 t / min) ・ Melted steel supply rate from upper discharge hole Q ': 0.76Q (consumption rate of molten steel solidified above the height center of the magnetic pole) Q: 0.76 times) Solute element (pure Ni wire) Supply position of pure Ni wire (horizontal distance from upper discharge hole to both ends): 0.1 m Immersion position of pure Ni wire supply pipe in mold (up to upper discharge hole) Height distance): 0.12m

It is known that the growth thickness d (m) of the solidified shell in the above continuous casting machine is given by the following equation (7). d = 0.022 × (L / Vc) ^0.5 --- (7) where L is the distance (m) from the molten metal level to the height center of the magnetic pole, and Vc is the casting speed (m / min). Therefore, it can be seen from the above formula (7) that the solidified shell thickness at the upper and lower pool boundaries is about 10.2 mm. As a result, Q =
It becomes 0.112 t / min. On the other hand, Q'is known to be 17.5% of the total throughput based on the water model, and Q '= 0.0853 t / min. Therefore, Q '= 0.76Q
Becomes The superheat degree of molten steel in the tundish during casting is
It was in the range of 25 to 65 ° C.

Under the above-mentioned casting conditions, a high frequency induction heating coil (frequency: 44 kHz, coil length: 500 mm) as shown in FIG. 1 was used as a heating means. 8 mm diameter nickel wire 8 m / min
(3.5 kg / min) while heating and melting while feeding,
It was supplied into molten steel. The molten nickel is injected into the molten steel in the mold through an introduction tube such as Si ₃ N ₄ (+ BN) or AlON (+ BN) heated to 1450 ° C or higher with a Kanthal wire or platinum wire as a heat-retaining path. did. The above refractory material was determined from the viewpoints of excellent thermal shock resistance, low thermal conductivity and low wettability.

Example 2 Under the same casting conditions as in Example 1 above, an arc heating device having the structure shown in FIG. 4 was used as the heating means. In the figure, number 18 is a primary power transformer, 19 is a secondary power transformer, 20 is a tundish, 21 is a molten steel side power supply circuit, 22
Is a wire side power supply circuit, and 23 is an immersion electrode. Even when this arc heating device is used, the geometrical arrangement of the wire feeding device and the like is almost the same as in FIG. However, when using an arc heating device, if the wire is made to proceed in a submerged state (that is, directly above the molten steel in the mold powder layer) by adjusting the arc current / voltage and the wire feed rate, It is not necessary to provide a heat-retaining path used in the high-frequency heating device until it is supplied to the molten steel after melting. If not,
In order to cool the molten metal after melting and prevent the molten metal from hitting the mold powder into the molten steel, it is preferable to supply the molten metal through a heat-insulated route. Now,
In this Example 2, arc heating melting was performed while supplying a nickel wire having a diameter of 8 mm onto the molten steel through a wire guide that also serves as an electrode. The wire was fed into the molten steel in the mold while melting in the powder. The ground contact with molten steel is
The immersion electrode 23 was embedded in the refractory in the tundish.

For comparison, an experiment was also conducted under the same conditions as in the above-mentioned conforming example, in the case where the wire was not melted by heating. However, in this case, since the melting temperature in the mold was drastically lowered, the wire feeding rate was limited to 1 kg / min.

FIG. 5 shows the results of investigations on the occurrence of defects in the cast pieces obtained according to Examples 1 and 2 and Comparative Example of the present invention. Here, the defect occurrence status of the slab is as follows.
Inclusions and powdery defects having a size of 500 μm or more were observed and investigated, and the amount thereof was evaluated by a relative value when Example 1 was set to 1.0. As is clear from the figure, in both Examples 1 and 2, the defects in the surface layer of the cast slab were significantly reduced as compared with the comparative example. The observed defects are
The defects were powdery defects and alumina defects due to entrainment of powder. In the comparative example, since the wire was supplied without heating, the inclusion of unmelted powder was increased, and the molten layer thickness was decreased due to the decrease of the temperature inside the mold, and the absorption of alumina into the powder was decreased. It is considered that the number of defects has increased.

[0039]

As described above, according to the present invention, it becomes possible to stably supply a large amount of alloying elements to the upper pool in the mold, and as a result, the solute element concentration in the surface layer of the slab is extremely small. Therefore, a uniform slab can be stably manufactured. Further, according to the present invention, addition of an alloying element does not cause a decrease in casting temperature, so that stable casting can be performed without causing a slab defect and reducing productivity.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example of how to add a solute element into a mold when high frequency induction heating is used as a heating means.

FIG. 2 is a diagram showing a relationship between a wire heating temperature when supplying a nickel wire and a temperature decrease amount of molten steel in a mold.

FIG. 3 is a diagram showing an example of a procedure for injecting molten steel into a mold using a three-hole nozzle.

FIG. 4 shows a case where arc heating is used as a heating means,
It is a schematic diagram which shows an example of the addition point of a solute element in a casting_mold | template.

FIG. 5 is a diagram showing the occurrence status of a cast slab defect in comparison between Examples 1 and 2 and a comparative example.

[Explanation of symbols]

1 wire reel 2 High frequency induction heating coil 3 Magnetic shield material 4 Introductory pipe made of refractory material 5 heating wire 6 wires (nickel wire) 6'molten nickel 7 Molten steel 8 molds 9 Immersion nozzle 10 magnetic poles 11 Center of magnetic pole height 12 Lower discharge hole of immersion nozzle 13 Upper discharge hole of immersion nozzle 14 Jet from lower discharge hole 15 Jet from upper discharge hole 16 DC magnetic field backflow from the lower pool to the upper pool 17 solidified shell 18 Primary power transformer 19 Secondary power transformer 20 tundish 21 Molten steel side power supply circuit 22 Wire side power supply circuit 23 Immersion electrode

Continued front page    (72) Inventor Yukio Takahashi             1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Made in Kawasaki             Technical Research Institute of Iron Co., Ltd. F-term (reference) 4E004 MB08 MB11 MB14 NC01

Claims (6)

[Claims] 1. In continuous casting of molten steel, a DC magnetic field band is applied across the entire width of the slab at a position a certain distance below the level of the molten metal in the continuous casting mold in the casting direction. While injecting molten steel into the molten steel pool in the DC magnetic field band or above the DC magnetic field band using an immersion nozzle, a specific solute element is added to the molten steel in the DC magnetic field band or above the DC magnetic field band. By adding
Increase the concentration of the solute element in the molten steel in the upper pool,
Therefore, in the method for producing a continuous cast slab consisting of adjusting the solute element concentration in the surface layer of the slab, when adding a specific solute element to the molten steel in the upper pool, a wire containing the solute element is placed above the mold. In the method for producing a continuously cast slab, the molten steel is supplied to the molten steel in a state of being heated and melted by a heating means. 2. The continuous cast slab according to claim 1, wherein the wire is heated and melted by a heating means to form a molten metal, and the molten metal is injected into the molten steel in the mold through a heat-insulated path. Manufacturing method. 3. The method for producing a continuously cast slab according to claim 1, wherein the heating means is high frequency induction heating. 4. The method for producing a continuously cast slab according to claim 3, wherein the heat-retained path is curved downward above the mold. 5. The method for producing a continuously cast slab according to any one of claims 3 to 4, wherein the wire diameter is 3 to 20 mm and the frequency in high frequency induction heating is 30 to 50 kHz. 6. The method for producing a continuously cast slab according to claim 1, wherein the heating means is arc heating.