JP2002001500A - Production method for continuous casting product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method which can easily control supply of molten metal and also can stably produce a double layered casting without fluctuation of the solute element concentration in the breadthwise direction of the surface of the casting and generation of powdered defect. SOLUTION: Molten metal is injected by using a single immersed nozzle into a direct current magnetic field zone impressed in the central part in the vertical direction of the casting mold or a pool of the upper part than the direct current magnetic field zone in the state that a direct current magnetic zone is impressed over the whole width of the casting in the direction crossing the thickness of the casting by two independent stages of magnetic poles, in respective sections of the upper part of casting mold including the molten metal surface level in the continuous casting mold and the vertically central part of the casting mold separated downward from the above part by a specified distance, and a specified solute element is added into the direct current magnetic zone or the upper molten metal than the direct current magnetic zone. In this way, the concentration of solute element in the molten metal in the upper pool is increased to adjust the solute element concentration of the surface part of the casting. In the production method of the continuous casting product in which the solute element concentration of the surface part of the casting is adjusted, with regard to impression of magnetic field to the upper part of the casting mold, in addition to the above direct current magnetic field, a fixed alternate current magnetic field is doubly applied to the molten metal level.

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 continuous cast slab having a gradient composition in which the concentration of a specific solute element in a surface layer is higher than that in the inside of a slab. Is intended to further uniform the concentration distribution over the width direction.

[0002]

2. Description of the Related Art Conventionally, various methods have been proposed for producing a slab having a composition different from that of a surface layer in a surface layer portion by continuous casting. For example, Japanese Patent Publication No. 3-20295 discloses that a direct magnetic flux is applied over the entire width of a slab in a direction perpendicular to the casting direction at a position below a fixed distance from a molten metal level in a continuous casting mold. A method of obtaining a multilayer slab by supplying different metals above and below a static magnetic field zone formed by a magnetic flux as a boundary is described.

[0003] Japanese Patent Application Laid-Open No. Hei 7-51801 discloses that molten steel is vertically injected together with gas into a mold for continuous casting.
A direct current magnetic field is applied to the entire width in the mold above the molten steel injection position to decelerate the upward flow of the molten steel, and an element different from the molten steel component is added to the molten steel above the direct current magnetic field application position. A method for producing a multi-layered steel sheet comprising forming a surface layer of an alloy steel on a steel surface by using the molten steel at an upper portion as an alloy molten steel by levitation stirring of the injected gas is described.

Further, Japanese Patent Application Laid-Open No. 8-290236 discloses that a mold powder contains an alloy element to be concentrated on the surface layer of a slab, and a molten steel pool in the mold is stirred by an electromagnetic stirrer installed above the mold. A stir flow is formed in the horizontal cross section of the mold, and a DC magnetic field having a uniform magnetic flux density in the width direction is applied below the mold in the thickness direction of the mold to form a damping zone in the molten steel pool in the mold. A method has been proposed in which the concentration of alloying elements in the surface layer portion of a slab is made higher than that in an inner layer by casting while supplying molten steel from a nozzle downward.

In addition, it is possible to reduce inclusions in the slab,
A flow control method using an electromagnet has been proposed and has been put to practical use in order to prevent the fluctuation of the molten metal level at the time of casting and to prevent the powder from being caught in the slab. For example, JP-A-1-105817 proposes a method in which a magnetic field is applied to a molten metal surface (meniscus) and upper and lower two stages below the mold in a direction crossing the thickness of the slab over the entire width of the mold.

However, in the method described in Japanese Patent Publication No. 3-20295, the molten steel for the surface layer and the molten steel for the inside of the slab are secured in two separate tundishes, and the solidification speed in the upper and lower portions of the magnetic field zone is reduced. Since it is necessary to perform extremely difficult control of independently supplying a corresponding amount of molten steel from each tundish, stable production is difficult, and as a result, there is a problem that the product yield is reduced. In addition, Japanese Patent Application Laid-Open No. 7-51801
In the production method described in the publication, the molten steel from the tundish is supplied only to the lower part of the magnetic field zone so as to maintain the level of the molten metal in the mold constant, and is not supplied to the upper part of the magnetic field zone.
Although the shortage corresponding to the solidification amount in the upper part of the magnetic field zone naturally flows in from the lower part of the magnetic field zone, the above-mentioned problem does not occur. Due to the influence, the gas flows almost uniformly in the width direction, so that there is a problem that the extreme concentration difference between the portion where the solute element is added and the portion far from the portion cannot be eliminated only by the stirring effect of the bubbles.

Further, in the method disclosed in JP-A-8-290236, since the thickness of the concentrated layer formed by adding an alloy element from powder is too small, a slab having a sufficiently thick concentrated layer is used. There was a problem that cannot be manufactured. Usually, the thickness of the concentrated layer formed by adding an alloy from powder is at most a few millimeters, and generally cannot be said to be a sufficient thickness for the concentration of the surface layer portion.

In order to solve the above-mentioned problems, the present inventors have first attempted to solve the above problems at the upper part of the mold including the level of the molten metal in the continuous casting mold and at the center of the mold at a certain distance below the upper part of the mold. In a state in which a DC magnetic field band is applied across the entire width of the slab in a direction crossing the thickness of the slab by two upper and lower magnetic poles (electromagnets) independently controlled in current, the DC magnetic field band applied to the center of the mold or By injecting molten steel into the pool above the DC magnetic field zone using a single immersion nozzle, and adding a specific solute element to the molten steel within the DC magnetic field zone or above the DC magnetic field zone. Proposed a method for producing a continuous cast slab comprising increasing the concentration of the solute element in the molten steel in the upper pool to adjust the concentration of the solute element in the surface layer of the slab (Japanese Patent Application No. 2000-043711).

According to the above-mentioned method, it is possible to form a surface-concentrated layer having a sufficient thickness while reducing the change in the concentration of solute elements in the surface layer of a slab, and to control the flow of a meniscus to form a mold powder. Can be effectively prevented. However, when a product plate was manufactured using the obtained continuous cast slab as a material, for example, when a corrosion resistance test was performed on a product plate in which Ni was concentrated on the surface to improve the corrosion resistance, local corrosion resistance was found. There were occasional cases where the deterioration of the film occurred.

[0010]

DISCLOSURE OF THE INVENTION The present invention advantageously solves the above-mentioned problems, and achieves a more uniform solute element concentration distribution in the surface layer of a slab, and achieves local characteristics in a product plate. An object of the present invention is to propose an advantageous method for producing a continuous cast slab without causing deterioration or the like.

[0011]

[Means for Solving the Problems] As described above, Japanese Patent Application No.
When a continuous cast slab manufactured according to the method described in the specification of 00-043711 is used as a raw material, local property deterioration may occur in a product plate. Therefore, the inventors conducted a thorough investigation on the above causes and found that
In the method described in the specification of 2000-043711, it has been found that, in some cases, the concentration distribution of the solute element in the surface layer portion of the slab is not sufficiently uniform, and local concentration variation occurs.

FIG. 1 (a) shows the concentration distribution (solute width direction) of solute elements (Ni) in the surface layer of a slab of a continuous cast slab manufactured according to the method described in Japanese Patent Application No. 2000-043711. The result of the examination is shown. As shown in the figure, local variations in the concentration of solute elements were observed in the outermost layer of the slab. Then, as a result of further detailed investigation, the following became clear. 1) When the position where the solute element is added is changed, the variation in the concentration of the surface layer changes depending on the case. 2) Variation is particularly large in the surface layer of the slab.

Investigation of the cause revealed that the situation in which the solute element was mixed with the molten steel after being added to the upper pool was different depending on the element addition position and the nozzle used. As a result, there is a problem that the variation in the element concentration in the width direction is particularly large on the upper side of the upper pool (portion near the meniscus). It is probable that this problem could not be confirmed in the previous survey because multiple samples were taken only at the slab surface depth of 10 mm.

[0014] The inventors of the present invention have conducted intensive studies to prevent the above-mentioned local concentration variation, and as a result, have found that the method of manufacturing a continuous cast slab described in Japanese Patent Application No. 2000-043711. As for the application of a magnetic field at the upper part of the mold, it has been found that it is extremely effective to apply a DC magnetic field in which a fixed AC magnetic field is superimposed on a molten metal level, rather than a DC magnetic field. The present invention is based on the above findings.

That is, the gist of the present invention is as follows. 1. At the time of continuous casting of molten metal, the upper part of the mold including the level of the molten metal in the continuous casting mold and the middle part in the height direction of the mold separated by a certain distance below the upper and lower parts of the upper and lower stages of the current control independently. In a state in which a DC magnetic field is applied across the entire width of the slab by a magnetic pole (electromagnet) in a direction transverse to the thickness of the slab, the DC magnetic field is applied to the center of the mold in the height direction of the mold or in a pool above the DC magnetic field band. Injecting molten steel using a single immersion nozzle, and adding a specific solute element to the molten steel in or above the DC magnetic field zone, thereby forming the solute element for the molten steel in the upper pool. In the method for producing a continuous cast slab comprising adjusting the solute element concentration of the slab surface layer by increasing the concentration of
A method for producing a continuous cast slab, wherein a fixed AC magnetic field is superimposed on a molten metal level and applied in addition to the above-described DC magnetic field in applying a magnetic field on an upper portion of a mold.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings. 2, 3 and 4 illustrate how to inject molten steel according to the present invention. The example of FIG. 2 is a case where a single-hole straight nozzle is used as the immersion nozzle, in which molten steel is supplied in a substantially vertical direction. The example in FIG. 3 is a case where a so-called two-hole nozzle having two discharge holes and inclining the angle of the jet from each discharge hole is used as the immersion nozzle. The example of FIG. 4 is a case where a three-hole nozzle having a main discharge hole at the bottom and two sub-holes on the side is used as the immersion nozzle. In the figure, reference numeral 1 denotes a mold, 2 denotes an immersion nozzle (2a: straight nozzle, 2b: two-hole nozzle, 2
c: three-hole nozzle), 3a, 3b are upper and lower two-stage magnetic poles (electromagnets) arranged at the top of the mold and at the center in the height direction, respectively
With these magnetic poles 3a and 3b, a DC magnetic field can be independently applied over the entire width of the slab in the thickness direction of the slab. In addition, the upper magnetic pole 3a has a mechanism that can simultaneously apply an alternating magnetic field.

That is, the upper magnetic pole 3a is wound in common with an electromagnetic brake coil (direct current energizing coil) for passing a direct current, and a low frequency magnetic field coil (alternating current coil) for passing a fixed type alternating current. With such an electrode structure, a DC magnetic field on which a fixed AC magnetic field is superimposed can be applied. FIG. 5 is a perspective view of this state as viewed from the back side of the short side of the mold. In FIG. 5, 3a-1 is a direct current energizing coil, 3a-2 is an alternating current energizing coil, and 3a-3 is an iron core. The immersion nozzle 2 is disposed between the upper and lower magnetic poles 3a and 3b.

The number 4 indicates the center of the height of the magnetic pole.
Is the height center of the upper magnetic pole 3a, and 4b is the height center of the lower magnetic pole 3b. Further, 5 is a discharge hole of the immersion nozzle 2, 6 is a jet from the immersion nozzle 2, and 7 is a reverse flow (upflow) from the lower pool to the upper pool in the DC magnetic field band. 8,8 '
Is the solute element (wire), X is the position where the solute is added,
Reference numeral 9 denotes a solidified shell. In the drawings, w is the width of the mold, θ is the angle of the immersion nozzle discharge hole (a downward angle with the horizontal direction being 0), h is the distance from the lower end of the immersion nozzle discharge hole to the height center of the lower magnetic pole, d represents the distance from the lower end of the immersion nozzle discharge hole to the upper end of the lower magnetic pole.

Now, referring to FIGS. 2 and 3,
Most of the molten steel jet 6 supplied from the immersion nozzle 2 once flows into the lower pool. However, since there is no supply source of the molten steel to the upper pool, only a necessary amount of the molten steel once flowing into the lower pool is re-used in the upper pool. Will flow back to
In FIG. 4 as well, the supply of the main molten steel is performed from the lower main hole, and thus the molten steel flowing into the lower pool flows back to the upper pool again. Therefore, in the present invention, as in the method described in Japanese Patent Application Laid-Open No. Hei 7-51801, there is no problem regarding the control of the supply speed of molten steel.

In the present invention, since the molten steel jet 6 supplied from the immersion nozzle 2 crosses the DC magnetic field zone, the jet 6
, An induced current 10 is generated as shown in FIG. As a result, the interaction between the induced current 10 and the DC magnetic field 11 generates an electromagnetic force 12 as shown in FIG. In this way, a so-called electromagnetic braking force is generated in the jet portion in a direction opposite to that of the jet 6, but such an induced current is inevitably generated on both sides of the jet portion. And the flow in the opposite direction is likely to occur on both sides of the jet.

As a result, as shown in FIG. 2, inflow of molten steel from the lower pool in the magnetic field zone to the upper pool (backflow 7) occurs, so that the upper pool has a rotating flow as shown in FIG. Is generated and stirring is promoted, so that the concentration distribution of solute elements in the molten steel in the upper pool becomes uniform. Further, since the downward jet from the nozzle is decelerated when passing through the magnetic field zone, the entrapment which causes an internal defect to fall down is reduced, and the internal quality is improved.

As described above, in the present invention, it is necessary to penetrate the magnetic field zone before the jet from the immersion nozzle diffuses, so that it is important to appropriately set the nozzle position, the discharge angle, and the magnetic field application position. It is. Therefore, as a result of various studies on this point, it has been found that it is preferable that the following relationship be satisfied with respect to the position of the nozzle, the ejection angle of the main ejection hole, and the application position of the magnetic field. h <(1/2) · w · tanθ --- (1) 0 <d ≦ 0.3 --- (2) where θ: downward angle (°) of the immersion nozzle discharge hole w: width direction of the mold H: distance from the lower end of the immersion nozzle discharge hole to the center of height of the magnetic pole (m) d: distance from the lower end of the immersion nozzle discharge hole to the upper end of the magnetic pole (m)

Equations (1) and (2) above are geometrically important conditions for penetrating the magnetic field zone before the jet from the immersion nozzle diffuses. If the operation is carried out under the conditions satisfying the formula, the solute elements are more evenly added only to the upper pool, effectively producing a slab having a high concentration of solute elements only in the surface layer of the slab. You can.

In the above example, the case where the immersion nozzle is a single-hole straight nozzle has been mainly described. However, in the present invention, it is important to locally generate a molten steel inflow portion from the lower pool to the upper pool. Therefore, even in the case of a two-hole nozzle as shown in FIG. 3 and a three-hole nozzle having a total of three discharge holes in the lower portion and both side portions as shown in FIG. If the above conditions (1) and (2) are satisfied, it is possible to effectively generate a desired local inflow site. Further, in order to further enhance the effect of locally forming the inflow portion and the effect of attenuating the nozzle jet, the position of the nozzle outlet is preferably located above the center of the magnetic pole.

Next, the effect of the magnetic field will be described. The lower magnetic field is
Only a DC magnetic field is applied to prevent additional elements and inclusions from entering the lower pool. Regarding the strength of the applied magnetic field in the lower stage, if it is too small, the braking effect by the magnetic field is weakened, and the molten steel in the upper pool and the lower pool may be mixed.On the other hand, if it is too strong, the inflow into the upper pool is strong. Since the molten steel in the upper pool is excessively supplied to the upper pool more than necessary, and as a result, the molten steel in the upper pool may flow out at a position distant from the inflow position, the applied magnetic field is applied to the upper pool and the lower pool. It is important that the strength is appropriate so as not to cause mixing of molten steel in the pool or poor uniform dissolution of alloy elements, and it is usually preferable to be about 0.2 to 0.3 T. It is also injected into the nozzle as well
If the flow rate of Ar gas is too high, the flow into the upper pool becomes too strong, so the flow rate of Ar gas is desirably 20 l / min or less.

Next, the upper magnetic field will be described. If the flow of the meniscus is small, the flow in the mold width direction disappears after dissolving the added solute element by upward flow,
Variations in element concentration in the width direction occur. In addition, when the meniscus flow is small, powder trapping is likely to occur due to a decrease in the temperature of the meniscus. On the other hand, if the flow of the meniscus is too large, it is advantageous in making the added element uniform in the width direction, but it has been found that the mold powder is caught by the meniscus, and the powder adheres to the shell to cause a defect. That is, while a certain amount of flow is required in the vicinity of the solidified shell, if the flow occurs over the entire meniscus, defects such as powder entrainment increase. Therefore, a method that can independently control the flow around the solidified shell and the entire meniscus is desired.

Therefore, in the present invention, the current of the lower magnetic field and the current of the upper magnetic field are controlled independently. In particular, for the upper magnetic field, a magnetic field obtained by superimposing a fixed AC magnetic field (fixed AC magnetic field) on a DC magnetic field is applied. Is used. Here, the fixed AC magnetic field refers to the phase of the intensity distribution waveform in the casting width direction (valley of distribution or The peak moves with time, whereas the phase does not move in a fixed direction. A single-phase or multi-phase AC current flows through the AC current-carrying coil that generates the AC magnetic field.

That is, as shown in FIG. 8, an AC / DC superimposed magnetic field which produces a magnetic flux density having a waveform as shown in FIG. 9 is generated in the casting thickness direction by the AC coil 3a-2 and the DC coil 3a-1. When applied, an electromagnetic force having a magnetic flux density of about several thousand gauss and an AC component can be applied inside the mold.

The AC component (electromagnetic pumping force) of the electromagnetic force causes disturbance, heat and mass transfer are activated, and the washing effect in the solidified shell is promoted. Also, the electromagnetic pumping force is large near the solidified shell,
It is small at the center of the casting thickness. On the other hand, since the DC magnetic field hardly attenuates in the casting thickness direction, the DC component (electromagnetic braking force) of the electromagnetic force used for the molten steel flow braking becomes dominant near the center of the casting thickness due to the periodic fluctuation attenuated. Accordingly, the flow of the molten steel in the vicinity of the solidified shell can be activated while the general flow of the meniscus is calmed down. As a result, as compared with the conventional application of only a static magnetic field, not only can the concentration distribution of the added solute element in the width direction be made more uniform, but it is also possible to trap inclusions at the solidification interface without causing powder entrainment or the like. It can be reduced effectively.

FIG. 1 (b) shows a continuous cast slab when a cast slab is manufactured while applying a DC magnetic field as a lower magnetic field and applying an AC / DC superimposed magnetic field as an upper magnetic field according to the present invention. Element (Ni) in the surface layer of cast slab
Shows the results of examining the concentration distribution (in the direction of the slab width).
As shown in the figure, according to the present invention, it can be seen that local variations in the concentration of solute elements in the surface layer of the slab are significantly reduced.

Here, the frequency of the fixed AC magnetic field is preferably about 0.5 to 10 Hz. And
By changing this frequency, the depth of penetration of the magnetic force due to the skin effect can be changed, and the flow of molten steel at a desired location can be freely controlled. In other words, the higher the frequency, the more the stirring force can be applied near the surface.However, if the frequency exceeds 10 Hz, the magnetic force reaches only the solidified shell and the mold copper (steel) plate, and the molten steel cannot be sufficiently stirred. The upper limit of the frequency is about 10 Hz. On the other hand, the lower the frequency, the more the magnetic force can spread to the inside of the molten steel, but the lower the frequency.
If it is less than 5 Hz, effective stirring power cannot be obtained, so the lower limit of the frequency is about 0.5 Hz. This frequency range belongs to the so-called low frequency range. The more preferable frequency range is 3
７7 Hz.

As described above, the action of the AC moving magnetic field is stronger near the solidified shell and weaker farther (inside the mold). On the other hand, the DC magnetic field acts irrespective of the vicinity of the solidified shell and the inside of the mold, so that the stirring effect can be increased near the solidified shell and the braking effect can be increased inside. Therefore, a flow near the solidified shell, which is necessary for homogenizing the alloy element in the width direction, and a quiet flow over the entire meniscus that suppresses powder entrainment can be achieved at the same time.

The upper magnetic field generator (magnetic pole) according to the present invention includes an electromagnetic brake coil for supplying a direct current and a low-frequency electromagnetic stirring coil for supplying an alternating current, and these coils are commonly used. By winding around the iron core, a time-varying magnetic field can be generated from the common iron core, so that the electromagnetic brake and the electromagnetic stirring can be freely operated at the same position. In order to obtain a more uniform washing effect in the width direction of the slab, it is more effective to branch the tip of the iron core into a plurality of magnetic poles as shown in FIG. It is. On the other hand, the DC magnetic field may be wound around the iron core.

The effect of the static magnetic field on the upper magnetic pole is as follows.
Since the purpose is to rectify the meniscus and prevent entrapment of the mold powder, the strength required for the lower magnetic field is unnecessary. Furthermore, it is necessary to use an appropriate magnetic field in order to prevent a decrease in efficiency due to an interference effect with an AC magnetic field (as a result, heat is generated in the coil itself and power efficiency is reduced). Usually, a sufficient effect can be obtained by applying a static magnetic field of 0.1 to 0.2 T. When the DC magnetic field generator of the present invention is used, the typical flow velocity (1/4 width / center thickness) of the meniscus is
Controlling within the range of 0.1 to 0.6 m / s is suitable for preventing mold powder defects in the solidified shell and uniformizing the width of the added element in the width direction. If the typical flow velocity of the meniscus is less than 0.1 m / s, it is difficult to sufficiently eliminate the density difference in the width direction, while if it exceeds 0.6 m / s, there is a concern that powder defects may increase.

With respect to the width (height direction) of the upper and lower DC magnetic field bands to be applied, if the width is too small, the braking effect is not sufficient, while if it is too large, the power supply capacity or coil required to generate a magnetic field is required. Since the size becomes large and the equipment cost increases, the width in the height direction of the magnetic pole is preferably about 0.1 to 0.5 m.

[0036]

EXAMPLE Using the continuous casting mold shown in FIG. 3, under the following conditions:
Continuous cast slabs were produced.・ Inner diameter of the mold Long side: 1.7 m, Short side: 0.26 m ・ Lower DC magnetic field Applied position: 0.58 m below the mold level in the mold (to the center of the magnetic pole height) Applied magnetic field strength: 0.3 T Lower coil height Applied position: 0.1m below mold level (to the center of magnetic pole height) Upper applied magnetic field strength: changed depending on conditions Upper coil height: 0.18m The structure is divided into 12 branches, and each branch section forms a magnetic pole. An AC current-carrying coil is wound around each magnetic pole, and a DC current-carrying coil is wound around the common core of the iron core.・ Immersion nozzle 2-hole nozzle (discharge angle θ = 20 °, 25 °) ・ Solute element (pure Ni wire) Supply position of pure Ni wire: 0.1 m from short piece (center of thickness) Melting position of pure Ni wire: 0.05m from mold level in mold
Downward ・ Casting speed 1.7, 2.0 m / min

It is known that the growth thickness t (m) of the solidified shell in the above continuous caster is given by the following equation (3). t = 0.022 × (L / Vc) ^0.5 --- (3) where L is the distance (m) from the level of the molten metal to the center of the height of the lower magnetic pole, and Vc is the casting speed (m / min). . Therefore, from the above equation (3), it can be seen that the thickness of the solidified shell at the boundary between the upper and lower pools is about 12 to 13 mm.

Now, a continuous casting was performed under the above-mentioned conditions while changing the casting speed, the mold width, the type of the nozzle, and the like, and the result of examining the relationship between the Ni concentration distribution ratio in the width direction of the surface layer of the slab and the powder defect index was examined. Is shown in Table 1. Here, the concentration distribution was analyzed by collecting drill samples from a plurality of positions in the width direction (10 mm intervals) at both the surface portion depth: 10 mm and the surface portion: 1 mm. Depth at each position: The average value of the analysis values at 10 mm and 1 mm was determined, and the ratio of the maximum value to the minimum value in the width direction was defined as the concentration distribution ratio. For the upper magnetic pole, a DC magnetic field was applied in the range of 0.10 to 0.22 T, and a low-frequency fixed AC magnetic field (0.08 T, 6 Hz) was applied. For comparison, the same two-hole nozzle was cast while controlling using an AC magnetic field in the upper part and a DC magnetic field in the lower part (Comparative Example 1,
2) was also investigated.

[0039]

[Table 1]

As is clear from the table, according to the present invention, Ni as a solute element could be uniformly concentrated over the entire width of the slab. In addition, according to the present invention, when the fixed AC magnetic field and the DC magnetic field are applied in a superimposed manner, it can be seen that the generation of powdery defects is suppressed even at the same meniscus flow velocity.

[0041]

As described above, according to the present invention, the molten steel can be supplied to the upper and lower pools of the magnetic field zone with a single dundish and a single immersion nozzle. It is possible to stably produce a slab having no variation in the solute element concentration across the width direction of one surface layer portion, and it is possible to significantly improve the product yield.

[Brief description of the drawings]

FIG. 1 (a) is a diagram showing the concentration distribution of solute elements in the surface layer of a slab (in the slab width direction) when a DC magnetic field is applied to both the upper and lower stages, and FIG. It is the figure which showed the concentration distribution (the slab width direction) of the solute element of the slab surface layer part at the time of applying an alternating current / DC superimposed magnetic field as a magnetic field and an upper magnetic field.

FIG. 2 is a schematic view showing an example of a molten steel injection procedure (when a single-hole straight nozzle is used) according to the present invention.

FIG. 3 is a schematic diagram showing an example of a molten steel injection procedure (when a two-hole nozzle is used) according to the present invention.

FIG. 4 is a schematic diagram showing an example of a molten steel injection procedure (when a three-hole nozzle is used) according to the present invention.

FIG. 5 is a perspective view seen from the back side of the mold.

FIG. 6 is an explanatory diagram of an induced current generated around a molten steel jet from a nozzle.

FIG. 7 is an explanatory diagram of an electromagnetic force generated around a molten steel jet from a nozzle.

FIG. 8 is a schematic view showing a plan cross section of an upper magnetic field generator suitable for use in the embodiment of the present invention.

FIG. 9 is a waveform diagram showing an example of a magnetic flux density by applying an AC / DC superimposed magnetic field.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Mold 2 Immersion nozzle 3 Magnetic pole (electromagnet) 3a-1 DC energizing coil 3a-2 AC energizing coil 3a-3 Iron core 4 Center of magnetic pole height 5 Immersion nozzle discharge hole 6 Jet from immersion nozzle 7 Lower pool of magnetic field zone Backflow (upflow) from the water to the upper pool 8 Solute element (wire) 9 Solidification shell 10 Induced current 11 DC magnetic field (direction of magnetic field) 12 Electromagnetic force 13 Existence range of jet from nozzle

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Koji Yamaguchi 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Inside the Technical Research Institute of Kawasaki Steel Co., Ltd. (72) Shuji Takeuchi 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Kawasaki 4E004 AA09 MB11 MB14 NB01 NC01

Claims (1)

[Claims] In the continuous casting of a molten metal, current is independently controlled in each of an upper portion of a mold including a metal surface level in a continuous casting mold and a central portion in a height direction of the mold which is separated by a predetermined distance below the upper portion. In a state in which a DC magnetic field is applied across the entire width of the slab by the two upper and lower magnetic poles (electromagnets) in a direction crossing the thickness of the slab, a DC magnetic field applied to the center of the mold in the height direction or from the DC magnetic field band is applied. Also in the upper pool,
By injecting molten steel using a single immersion nozzle and adding a specific solute element to the molten steel in or above the DC magnetic field band, the solute element of the molten steel in the upper pool is added. In the method for producing a continuous cast slab, which comprises increasing the concentration and adjusting the solute element concentration in the surface layer of the slab, the application of a magnetic field above the mold includes, in addition to the DC magnetic field described above, a fixed AC magnetic field at the level of the molten metal. A method for producing a continuous cast slab, wherein the method is applied in a superimposed manner.