JP2003126945A - Device for supplying molten steel for continuous casting and method for continuous casting using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device for supplying molten steel for continuous casting which can prevent Al oxides or the like in the molten steel from adhering to the internal face of an immersion nozzle or the like, and at the same time, generation of defects, and to provide a method for the continuous casting. SOLUTION: The device for supplying the molten steel for continuous casting is provided with a tundish 1 in which an upper nozzle 2 is provided at the bottom, a flow rate control mechanism 3 provided at the lower part of the upper nozzle 2, the immersion nozzle 4 constituted of a refractory having electroconductivity, one electrode 5 facing to an internal space of the tundish 1, the other electrode 6 provided to the immersion nozzle 4, and a power source 7 connected to the both electrodes 5, 6. The method for the continuous casting is constituted in such a manner that the molten steel is supplied into a mold by using the device for supplying the molten steel, while energizing between the internal face of the immersion nozzle 4 and the molten steel 8 passing through the inside of the immersion nozzle.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molten steel feeding device provided for continuous casting, and a continuous casting method which is effective for preventing clogging of a dipping nozzle or the like and for suppressing defects on a slab surface using the molten steel feeding device. It is a thing.

[0002]

2. Description of the Related Art Usually, as a method for continuously producing cast slabs, molten steel contained in a tundish is supplied from an immersion nozzle provided in the lower part of the molten steel to the upper part of a mold whose upper and lower sides are opened. A method is used in which a solidified shell is formed in a mold, and then the slab is continuously cast by withdrawing from the lower part.

At this time, when the molten steel deoxidized with Al is continuously cast, the oxide of Al in the molten steel easily adheres to the inner surface of the immersion nozzle, and the flow of the molten steel in the immersion nozzle is hindered. Therefore, when casting is performed using the immersion nozzle having a plurality of discharge holes, the discharge flow is not uniform and the specific discharge flow becomes strong, and the flow of the molten steel in the mold is likely to be a single flow. When the one-sided flow occurs, the mold powder added to the surface of the molten steel in the mold is caught in the molten steel, and the Al oxide or the like adhering to the inner surface of the immersion nozzle is peeled off, so that the molten steel is easily caught in the molten steel.

The mold powder and Al oxides caught in the molten steel in the mold are trapped by the solidified shell in the mold, which causes the powdery defects and the slag defects on the surface of the slab. And the like are likely to occur. These defects on the surface of the slab cause surface defects on the product hot-rolled from the slab.

Furthermore, when the amount of Al oxide deposited on the inner surface of the immersion nozzle becomes remarkable, so-called nozzle clogging occurs,
It becomes difficult to continue casting thereafter. At that time, although the nozzle clogging can be eliminated by cleaning the inner surface of the immersion nozzle with oxygen gas, the cleanliness of the cast piece is significantly deteriorated.

A method is known in which an inert gas is blown into the molten steel passing through the inside of the immersion nozzle in order to prevent the oxide of Al in the molten steel from adhering to the inner surface of the immersion nozzle (iron and steel, vol.66, S868), recently, various methods have been proposed as preventive methods applicable to operation. For example,
Japanese Patent Laid-Open No. 4-319055 discloses a method of blowing an inert gas into the molten steel passing through the immersion nozzle, and the method of blowing the inert gas into the molten steel according to the molten steel flow rate (t / min) passing through the immersion nozzle. A method of adjusting the amount of active gas (liter (Nl) / min) has been proposed.

Further, in JP-A-6-182513, while passing an alternating current or a direct current between the porous refractory for blowing gas provided on the inner wall of the immersion nozzle and the molten steel passing through the immersion nozzle, A method of blowing an inert gas into molten steel has been proposed. In this method, by blowing an inert gas into the molten steel, Al oxides and the like are prevented from adhering to the inner surface of the immersion nozzle, and by energizing between the inner wall of the immersion nozzle and the molten steel, the molten steel is electromagnetized. Force acts,
The bubbles of the inert gas blown in are promoted to separate from the blowing refractory, and the bubbles generated are made small. Therefore, the bubbles trapped in the solidified shell in the mold become small, and defects caused by the bubbles of the slab are unlikely to occur on the surface of the product hot-rolled from the slab.

However, in the methods proposed in these publications, the bubbles of the inert gas are hard to be trapped in the solidified shell in the mold. Therefore, if the amount of the inert gas blown is reduced, the molten steel inside the immersion nozzle is Al oxide cannot be prevented from adhering, and conversely, if it is attempted to prevent Al oxide in molten steel from adhering to the inner surface of the immersion nozzle, the amount of inert gas blown in will increase and A large number of bubbles of active gas are trapped in the solidified shell in the mold, and surface defects may occur in the product made of the cast pieces.

As described above, according to the conventional method, it is impossible to stably prevent the adhesion of the oxide of Al in the molten steel to the inner surface of the immersion nozzle. In addition, even if it is possible to prevent the oxide of Al in molten steel from adhering to the inner surface of the immersion nozzle, a bubble defect occurs in the surface layer of the slab and the surface of the product made from this slab is the surface. Defects may occur. Therefore, there is a demand for a method capable of stably and effectively preventing adhesion of oxides of Al in molten steel to the inner surface of the immersion nozzle without generating bubble defects on the surface of the slab.

[0010]

DISCLOSURE OF THE INVENTION The present invention prevents the oxide of Al in molten steel from adhering to the inner surface of the dipping nozzle, and the surface defects of the slab caused by the mold powder and the oxide of Al. It is an object of the present invention to provide a molten steel supply device for continuous casting capable of effectively preventing the occurrence of the above-mentioned phenomenon and the generation of surface defects of a product made of this slab, and a continuous casting method using this molten steel supply device.

[0011]

In order to solve the above problems, the present inventors have focused on the electrocapillary phenomenon as a method for preventing the adhesion of Al oxides in molten steel to the inner surface of the immersion nozzle. And repeated examination. That is, the electrocapillary phenomenon is a phenomenon in which the interfacial tension between an electrode and a solution present in an ionic solution changes depending on the potential of the electrode, and as a result of diligent examination of these phenomena, the following findings are obtained: I was able to.

The upper nozzle, the flow rate control mechanism and the dipping nozzle of the continuous casting apparatus are made of refractory materials, and some of these refractory materials have electron conductivity or ion conductivity at high temperatures. Therefore, in continuous casting, if a potential difference is applied between the refractory having electronic conductivity or ionic conductivity and molten steel at high temperature, electrocapillary phenomenon occurs at the contact interface between the two, and the tension at the interface decreases, The force of Al oxide in molten steel adhering to the surface of the refractory is suppressed, and it becomes difficult to adhere to the surface of the refractory.

Based on the above estimation, using a crucible of an experimental scale, a refractory rod having electrical conductivity and an electrode are immersed in molten steel, and the two are energized to provide a space between the rod and the electrode having refractory properties. An experiment was conducted to apply a potential difference to the. As a result, the amount of oxide such as Al oxide in the molten steel that adheres to the surface of the refractory decreases even if the potential difference is small.Also, regardless of whether the potential is positive or negative, the larger the absolute value of the potential difference, the surface of the refractory It was confirmed that the amount of Al oxides etc. adhering to the molten steel in the molten steel decreased.

Based on the above test results, a study on a method capable of preventing the adhesion of Al oxides in molten steel to the inner surface of the immersion nozzle is promoted, and a method for electrically conductive refractory material and molten steel passing through the immersion nozzle is provided. As a method of effectively energizing the device, attention was paid to electrically insulating a pair of electrodes. Generally, if the refractory used for insulation has an electrical resistivity (specific resistance) of 1 × 10 ⁵ Ω · m or more at room temperature, sufficient insulation can be secured, but at temperatures like molten steel. When the temperature becomes high, ionic conduction occurs, the electrical resistivity remarkably decreases, and the insulation performance decreases.

From the above phenomenon, when the electrical insulation performance between the pair of electrodes deteriorates, the current does not sufficiently flow in the molten steel passing through the immersion nozzle, and the current flows in the short circuit other than the molten steel. Therefore, it is not possible to obtain a sufficient effect of preventing adhesion of oxides of Al in molten steel to the inner surface of the immersion nozzle. Also, not only is the applied power wasted,
There is a danger that a minute discharge will occur due to an electric leakage to the outside, and an electric shock or a malfunction of peripheral devices may be caused.

When preheating a tundish, etc.,
Alternatively, in the case of hot reuse without preheating, in both cases, the casting was started by setting the initial electric resistance between one electrode and the other electrode to 500 Ω or more immediately before starting to supply molten steel to the tundish. During the period from the end of casting to the end of casting, sufficient current does not flow in the molten steel passing through the immersion nozzle, and it is possible to prevent the current from flowing to the short circuit other than the molten steel. In addition, the above "from the start of casting to the end of casting"
Is about 60 to 500 minutes, although it varies depending on the continuous casting machine, the size of the slab, the casting speed, the number of heats for continuous casting, and the like.

The electric resistance during casting, which is calculated from the current and voltage between the pair of electrodes, between the start and the end of casting, is the end of preheating of the tundish before supplying molten steel into the tundish. At the time, or when the tundish once used for casting is used for re-casting as it is without preheating, between the one electrode and the other electrode in the tundish before supplying molten steel into the tundish. It is desirable to set the electric resistance to less than 1/10 of the original electric resistance.

In other words, as the casting time elapses, the electrical resistance calculated from the current and the voltage between the pair of electrodes that pass through the immersion nozzle and have the molten steel as an electric circuit gradually increases. If the electrical resistance during casting becomes large after the gradual increase, current does not sufficiently flow in the molten steel passing through the immersion nozzle, and current begins to flow in a short circuit other than the molten steel. Therefore, by controlling the electric resistance during casting until the end of casting by less than 1/10 of the original electric resistance between one electrode immediately before supplying molten steel into the tundish and the other electrode,
More effectively, it is possible to sufficiently flow the electric current in the molten steel passing through the immersion nozzle and prevent the electric current from flowing in the short circuit other than the molten steel.

The present invention has been completed based on the above findings, and has as its gist the following molten steel supply devices (1) and (2) and the continuous casting methods (3) to (7).

(1) A tundish containing molten steel, an upper nozzle provided at the bottom of the tundish, a flow rate control mechanism for controlling the flow rate of the stored molten steel supplied to the mold, and a distribution of the supplied molten steel. A molten steel supply device comprising a dipping nozzle for making a pair of electrodes and a power source section connected to these electrodes, and an inner surface of the upper nozzle, a flow rate control mechanism or an immersion nozzle which is in contact with the molten steel is equal to or higher than the melting point of steel. And is made of a refractory material having electrical conductivity, and one electrode of the pair of electrodes reaches the internal space of any one of the tundish, the upper nozzle, the flow rate control mechanism and the immersion nozzle and contacts the molten steel. And the other electrode is provided in a portion made of the refractory material having electrical conductivity, which is used for continuous casting.

(2) In the molten steel feeding apparatus of (1) above, the electric conductivity of the refractory material having electric conductivity is 1 × 10 ³ at the melting point of steel.
It is preferably S / m or more and / or alumina graphite. Furthermore, in the molten steel supply device of the above (1), an insulator is provided between one electrode and the other electrode, and / or an upper nozzle without an electrode, a flow rate control mechanism, and It is desirable to equip any of the immersion nozzles with a gas blowing section.

(3) The molten steel contained in the tundish is supplied to the mold using the molten steel supply device described in (1) and (2) above, and the upper nozzle provided with the other electrode of the pair of electrodes, A continuous casting method characterized in that an electric current is applied between an inner surface of a flow rate control mechanism and an immersion nozzle and molten steel passing through the inside.

(4) When the molten steel contained in the tundish is supplied to the mold using the molten steel supply device described in (1) and (2) above, preheating of the tundish before supplying the molten steel into the tundish At the end, or if the tundish once used for casting is used for casting again without preheating, before supplying molten steel into the tundish,
The electric resistance between the one electrode and the other electrode is 500Ω.
The above is a continuous casting method characterized by the above.

(5) In the continuous casting method described in (4) above,
After starting casting, the electric resistance obtained from the current and voltage applied to the one electrode and the other electrode until the end, the preheating of the tundish before supplying molten steel into the tundish At the end, or
When the tundish once used for casting is used again for casting without being preheated, 1/10 of the electric resistance between the one electrode and the other electrode is supplied before the molten steel is supplied into the tundish. It is desirable to be less than.

(6) By the continuous casting method described in (3) to (5) above
The applied current density is 0.001A / cm ^TwoAbove 0.3A / cm^Two
Current and / or applied to be less than
It is desirable that the applied voltage be 0.5 V or more and 100 V or less.
Yes.

(7) When the molten steel contained in the tundish is supplied to the mold using the molten steel supply apparatus described in (1) and (2) above, at least the immersion nozzle has electrical conductivity above the melting point of the steel. It is made of a refractory and is provided with another electrode, and the immersion nozzle side is set to a negative potential, and a direct current is passed between the immersion nozzle and the molten steel passing through the immersion nozzle to prevent the immersion nozzle from blocking. A continuous casting method characterized by the above.

In the present invention, the material forming the dipping nozzle or the like is made of a refractory material having electrical conductivity above the melting point of the steel in order to make electricity flow between the refractory material and the molten steel. In the following description, "a refractory material having electrical conductivity at a melting point of steel or more" may be simply referred to as "a refractory material having electrical conductivity".

"At the end of preheating of the tundish before supplying molten steel into the tundish" defined in the above (4) and (5) of the present invention means the following.

That is, before the molten steel is supplied into the tundish and the continuous casting is started, the refractory provided inside the tundish, the upper nozzle, the gate for controlling the amount of molten steel supplied to the mold, and the immersion. Preheat refractories such as nozzles using combustion gas. This is to prevent damage to the refractories due to thermal shock during molten steel injection and to prevent the molten steel initially supplied from becoming metal and adhering to these refractories. At that time, the surface temperature of these refractories at the end of preheating is usually 800 to 1300 ° C.
Is. However, the target surface temperature after the preheating of these refractory materials depends on the casting work conditions such as the capacity of the tundish and the time from the start of supplying molten steel into the tundish until the start of supplying molten steel into the mold. Be different.

By the way, as an electric circuit between the pair of electrodes at the end of preheating in a state where molten steel is not supplied into the tundish, the refractory provided in the tundish, the upper nozzle, the gate, the immersion nozzle, etc. Objects and steel structures that support these refractories. The electrical resistance of these refractories and steel structures usually decreases with increasing temperature.

From these facts, "electrical resistance between one electrode and the other electrode at the end of preheating" means a refractory, an upper nozzle, a gate provided inside a tundish preheated to a target surface temperature. , It refers to the electrical resistance between one electrode and the other electrode in an electric circuit composed of refractory materials such as immersion nozzles and steel structures that support these refractory materials, and supplies molten steel into the tundish. It means the lowest electric resistance immediately before starting. In the following description, this electric resistance may be referred to as an “initial electric resistance”.

Similarly, "when the tundish once used for casting is used again for casting without being preheated, the molten steel is supplied into the tundish before being defined in the above (4) and (5) of the present invention. "Electrical resistance between one electrode and the other electrode in" means the following.

That is, in recent years, from the viewpoint of reducing the energy saving cost, so-called hot reuse of tundish has been carried out, in which the tundish is reused without cooling, in which case the tundish is preheated. In some cases, new molten steel may be directly supplied into the tundish without preheating. Even if it is not preheated, the surface temperature of the refractory inside the tundish is 1000-1400 ℃
Is the state of. It means the electric resistance between one electrode and the other electrode in the electric circuit composed of the refractory and the steel structure mentioned above in the high temperature state, and the electricity just before the start of supplying molten steel into the tundish. Resistance, that is, the original electrical resistance.

The "electrical resistance obtained from the current and voltage between one electrode and the other electrode between the start and the end of casting" defined in the above (5) of the present invention is It means the electrical resistance between one electrode and the other electrode that makes the molten steel supplied into the tundish into an electric circuit.
The electric resistance of the molten steel as an electric circuit increases with the elapse of casting time. Hereinafter, this electric resistance may be referred to as "electric resistance during casting".

[0035]

BEST MODE FOR CARRYING OUT THE INVENTION The contents of the molten steel supply apparatus and continuous casting method of the present invention are as follows: apparatus configuration, refractory material having electrical conductivity, insulation work, gas injection, current, voltage application, and negative potential of immersion nozzle. The items will be explained separately. 1. Apparatus Configuration The configuration of the molten steel supply apparatus of the present invention will be described based on FIGS. 1 to 4. FIG. 1 is a vertical sectional view schematically showing an example of the molten steel supply apparatus of the present invention. In the figure, a three-layer sliding gate is shown as a molten steel flow rate control mechanism, but the present invention is not limited to this type, and even if it is a two-layer type, a stopper is further used. It may be in a form of control.

In FIG. 1, the molten steel supply apparatus comprises a tundish 1 having an upper nozzle 2 at the bottom and an upper nozzle 2
A sliding gate 3 provided below the sliding gate 3, an immersion nozzle 4 provided subsequent to the sliding gate 3,
One electrode 5 provided on the sidewall of the tundish 1, and
The other electrode 6 provided in the immersion nozzle 4 and the power supply unit 7 connected to the one electrode 5 and the other electrode 6 are provided.
The shape of the tundish 1 for containing the molten steel 8 and the refractory lining may be those normally used.

The upper nozzle 2 provided at the bottom of the tundish 1 has a supply hole 2a for supplying the molten steel 8 in the tundish 1 to the lower part, and is made of a refractory material. The sliding gate 3 has a three-layer structure including an upper plate 31, a lower plate 32, and a movable plate 33 provided therebetween. The upper plate 31, the lower plate 32, and the movable plate 33 are made of a refractory material provided with flow holes 31a, 32a, 33a, respectively. Then, the movable plate 33 is horizontally moved by a drive mechanism (not shown) to control the supply amount of the molten steel 8 supplied to the lower portion.

The submerged nozzle 4 has two discharge holes 4a at the bottom, and the portion including these discharge holes 4a is inserted into the mold 9. The shape of the immersion nozzle 4 is not limited to that shown in the drawing. For example, the number of discharge holes 4a exceeds two, the inside of which has a step having a different diameter in the longitudinal direction, the inside of which is provided with a straightening vane in the longitudinal direction, the inside of which is provided with a spiral projection, and the interior is provided at the top. A double structure including a nozzle may be used.

One electrode 5 is provided so as to penetrate the side wall of the tundish 1, and when the tip reaches the internal space of the tundish 1 and the molten steel 8 is supplied into the tundish 1, the tip thereof is the molten steel. 8 is immersed. The surface area of one of the electrodes 5 in the portion which is immersed in the molten steel 8 and comes into contact with the molten steel 8 is
It should be 10 cm ² or more.

The material constituting the one electrode 5 is required to withstand a molten steel 8 in the tundish 1 for a long time and to have electric conductivity. Refractory metals such as tungsten,
Alternatively, these composite materials can be used.

As shown in FIG. 1, one of the electrodes 5 is attached to the tundish side wall by forming holes for attaching electrodes on the iron skin and the refractory, and penetrating the iron skin and the refractory to attach the electrode. It may be arranged, or may be immersed in the molten steel from above the surface of the molten steel 8 in the tundish. When a stopper is used as a mechanism for controlling the flow rate of molten steel into the mold, the stopper can be a refractory material having electrical conductivity, and this stopper can be one of the electrodes 5.

Further, the upper nozzle or the sliding gate may be made of a refractory material having electric conductivity, and they may be used as one of the electrodes 5. Since the same effect can be obtained in any case, it may be selected from the viewpoint of cost and ease of construction. However, when one electrode 5 is placed in the mold, current easily flows through the outer surface of the immersion nozzle, and it is not possible to effectively prevent Al in molten steel from adhering to the inner surface of the immersion nozzle. The method of arranging in can not be adopted.

Since the other electrode 6 does not come into direct contact with molten steel,
Metal electrodes or TiB with heat resistance up to about 1200 ℃
Refractory materials such as ₂ , ZrB ₂ , SiC and graphite may be used. Metals such as carbon steel, stainless steel, and Ni have better electric conductivity than these refractory materials, but have a problem that they react with carbon contained in the immersion nozzle to lower the melting point and melt. Therefore, when the heat load on the electrode is large, it is desirable to use an electrode made of a refractory material.

The other electrode 6 needs to be connected to a portion composed of an electrically conductive refractory material. The other electrode 6 shown in FIG. 1 has a cylindrical shape arranged from the vicinity of the upper end of the immersion nozzle 4 to slightly above the level of the molten steel in the mold 9, and is embedded in the refractory forming the immersion nozzle 4. There is. It is desirable that the other electrode 6 is provided so as to face the entire inner surface of the immersion nozzle 4, but if it is provided in a portion of the immersion nozzle 4 that is immersed in the molten steel, it may melt depending on the material. Therefore, the arrangement as shown in FIG. 1 is adopted.

If the other electrode 6 is cylindrical and arranged as described above, during continuous casting, the other electrode 6 and molten steel passing through the inner surface of the immersion nozzle 4 are in most of the immersion nozzle 4. As they approach each other, their distances become almost equal. Therefore, when the electric current passes through the refractory material forming the immersion nozzle 4, it is possible to prevent the voltage from partially dropping.

The other electrode 6 is not limited to the arrangement and shape shown in FIG. 1, but may be the one shown in FIGS. The same refractory material as the one electrode 5 can be used as the material forming the other electrode 6.

FIG. 2 is a longitudinal sectional view showing another example in which the other electrode 6 is embedded in the immersion nozzle 4. In the figure, the other electrode 6a is a rod-shaped body made of a metal or a conductive refractory, and is embedded in a part of the immersion nozzle 4 from the outer surface thereof. This embedding may be performed when the immersion nozzle 4 is manufactured by press sintering, or by providing a hole in the press sintered immersion nozzle 4.

If a material having a high electric conductivity is used as the refractory material that comes into contact with the molten steel, even if an electrode having such a simple structure is used, a local current is not generated and the effect is exhibited in a wide range. can do. The electrode 6a may have a shape that is embedded in the immersion nozzle 4 and has a tip provided with a portion parallel to the axis of the immersion nozzle 4.

FIG. 3 is a front view showing an example in which the other electrode 6 is attached to the outer surface of the immersion nozzle. In the figure, the other electrode 6b is a metal linear body or rod-shaped body,
It is wound around the outer surface of the immersion nozzle 4. The outer surface of the immersion nozzle 4 is usually coated with an antioxidant. Since this antioxidant has an insulating property, when the other electrode 6b is wound around the immersion nozzle 4, the coated antioxidant is removed.

FIG. 4 is a front view showing another example in which the other electrode 6 is attached to the outer surface of the immersion nozzle. In the figure, the other electrode 6c is a metal ring-shaped body which is partially open and has a tightening portion at the open portion.
After being fitted to the outer surface of the, it is tightened with bolts and nuts. Also in this case, the antioxidant coated on the outer surface of the immersion nozzle 4 is removed.

The power supply section 7 is connected to one electrode 5 and the other electrode 6 which are a pair of electrodes by an electric wiring 7a, and the electrodes 5 and 6 are energized when necessary.

In the apparatus for supplying molten steel shown in FIG. 1, the immersion nozzle 4 is made of a refractory material having electrical conductivity, but the inner surface of the upper nozzle 2 and the sliding gate 3 in contact with the molten steel is electrically conductive. It may be constituted by a refractory having. However, in the member provided with the other electrode 6, that is, in the immersion nozzle 4 in FIG. 1, the inner surface with which the molten steel contacts must be made of a refractory material having electrical conductivity.

In the apparatus for supplying molten steel shown in FIG. 1, the other electrode 6 is provided in the dipping nozzle 4 because the oxide of Al or the like is most likely to adhere to the inner surface of the dipping nozzle 4 during continuous casting. This is because electric current is supplied to the molten steel passing through the inner surface of the immersion nozzle 4.

When the immersion nozzle 4 is made of a refractory material having electrical conductivity, the entire immersion nozzle 4 can be made of the above refractory material having electrical conductivity. Further, the refractory of the immersion nozzle 4 may have a structure of two or more layers in the radial direction, strength and the like are secured in the outer layer portion, and the inner layer in contact with the molten steel may be the refractory material having the above-mentioned electrical conductivity. Further, a part of the inner layer or the outer layer may be made of a material having low electric conductivity such as high-purity alumina.

On the other hand, when Al oxide or the like tends to adhere to the sliding gate 3, the sliding gate 3 may be made of a refractory having electrical conductivity, and the other electrode 6 may be provided on the sliding gate 3. In addition, the upper nozzle 2, the sliding gate 3 and the immersion nozzle 4
2 or more of them may be made of a refractory material having electrical conductivity, and the other electrode 6 may be provided on these.

When the sliding gate 3 is made of a refractory material having electrical conductivity, the movable plate 33 having the narrowest passage and to which Al oxide or the like easily adheres is made of the refractory material having electrical conductivity described above. It is desirable to do. Also in this case, similarly to the upper nozzle 2, a structure having two or more layers in the radial direction can be used, and the refractory material having the electrical conductivity can be used as the refractory material on the inner surface in contact with the molten steel.

When one of the upper nozzle 2, the sliding gate 3 and the immersion nozzle 4 is made of a refractory having electric conductivity and the other electrode 6 is provided, the other electrode 6 is provided in the immersion nozzle 4. Is desirable. This is because, during the continuous casting, since the oxide of Al or the like adhered to the inner surface of the immersion nozzle 4 affects the stability of the continuous casting operation and the quality of the product, This is because electricity is supplied between the molten steel and the molten steel.

When the other electrode 6 is provided on a plurality of members, it is necessary to prevent a large difference in the resistance value of each circuit. This is because if the difference in resistance value is large, the current flows only in a specific path and hardly flows in the other paths, and the adhesion prevention effect cannot be obtained in the other paths. 2. Refractory Material Having Electrical Conductivity As the refractory material having electrical conductivity, the molten steel to be contained 8
It is preferable that the electric conductivity is 1 × 10 ² S / m or more at the melting point or higher, and it is more preferable that the electric conductivity is 1 × 10 ⁴ to 1 × 10 ⁶ S / m. Generally, as a refractory having electric conductivity, a refractory containing graphite as one of the main components such as alumina graphite, zirconia graphite and magnesia graphite, solid electrolyte, TiB ₂
And boride-based materials such as ZrB ₂ and the like. The characteristics of each material will be described below.

Alumina-graphite refractory material Alumina-graphite refractory material, which is often used for dipping nozzles and the like, preferably contains 5 to 35% by mass of graphite. When the content of graphite is 5% by mass or more, it can have electrical conductivity in the temperature range from room temperature to the molten state of steel. Further, if it is about 12% by mass or more, the electric conductivity is more than 1 × 10 ⁴ S / m, which is more preferable.

However, the content of graphite exceeds 35% by mass.
And the strength deteriorates. Corrosion resistance deteriorates against molten steel
However, the problem of melting loss occurs. This alumina graphite
Quality refractory is SiO_TwoUp to about 20% by mass
However, there is no problem when energizing. SiO _TwoIs mainly aluminum
Reduces the coefficient of thermal expansion of the nagraphite refractory material and reduces thermal shock
It is effective in preventing breakage due to In addition, SiO_Twoof
Alternatively, SiC may be contained.

Zirconia Graphite Refractory Material If the zirconia graphite refractory material is 5
It is desirable that the content is up to 20% by mass. When the content of graphite is 5% by mass or more, it has electrical conductivity in the temperature range from room temperature to the molten state of steel. Further, if it is about 10% by mass or more, the electric conductivity becomes 1 × 10 ⁴ S / m or more, which is more preferable. However, if the content of graphite exceeds 20% by mass, there is a problem that the strength decreases. Here, the upper limit of the graphite content is smaller than that of the alumina graphite refractory because the density of zirconia is higher than that of alumina, and the density change of the refractory itself when the graphite of low density is contained. Because it becomes larger.

Refractory of solid electrolyte For example, refractory of solid electrolyte such as zirconia solid electrolyte containing no graphite. This solid electrolyte refractory has electrical conductivity at the temperature of the molten state of steel.
However, the electric conductivity is about 1 × 10 ² S / at the melting temperature of molten steel.
It is about m, which is not a sufficient value. When such a material is used, the current flows in a short-circuited manner, and the current locally flows. Therefore, it becomes difficult to obtain the effect of preventing the adhesion of alumina or the like over a wide area.

In order to solve such a problem, FIG.
It is necessary to provide an immersion nozzle 4 having the other cylindrical electrode 6 embedded therein, as shown in, so that an equal current flows in a wide range. Based on such knowledge, in the molten steel supply apparatus of the present invention, the electric conductivity is 1 × 10 ³ S / at the melting point of molten steel.
It was specified that refractory materials of m or more should be used. Further, since the solid electrolyte has poor thermal shock resistance, it is difficult to apply it to a process of flowing molten steel after preheating such as continuous casting of molten steel. Further, there is a problem that the manufacturing cost of the refractory becomes high when such a material is used.

Boride refractory materials such as TiB ₂ and ZrB ₂ have an electric conductivity of 1 ×.
Since it is 10 ⁵ S / m or more, it can be used as a refractory for energizing steel.

As described above, a refractory material containing graphite as a main component or a boride refractory material can be used.
However, a boride-based refractory material has a high manufacturing cost, and it is difficult to form a large structure. Therefore, the boride-based refractory material can be used only in part when the molten steel flow path is used.

Therefore, a refractory containing graphite as a main component is suitable for the refractory targeted by the present invention.
Alumina-graphite refractory is desirable in view of thermal shock resistance, strength, erosion resistance and manufacturing cost. 3. Insulation Construction In the molten steel supply device of the present invention, among the upper nozzle 2, the sliding gate 3 and the dipping nozzle 4, which are made of a refractory material having electrical conductivity, a member provided with the other electrode 6 and one electrode 5 It is desirable to provide an insulator between and.

In the apparatus for supplying molten steel shown in FIG. 1, one electrode 5 is provided on the tundish 1 and the other electrode is provided on the immersion nozzle 4. In this case, the tundish 1 and one electrode are provided. 5, it is desirable to provide an insulator either between the tundish 1 and the upper nozzle 2, between the upper nozzle 2 and the sliding gate 3, or between the sliding gate 3 and the dipping nozzle 4.

As a result, when electricity is applied, one electrode 5
It is possible to prevent a short circuit from being formed between the immersion nozzle 4 provided with the other electrode 6 and the other. In this case, if an insulator is provided between the immersion nozzle 4 provided with the other electrode 6 and the sliding gate 3 adjacent thereto, it is possible to prevent a current from flowing through the sliding gate 3 when energized. , It can energize molten steel efficiently.

The level of insulation at this time is set at the end of preheating of the tundish before supplying molten steel into the tundish, or when the tundish once used for casting is used for recasting as it is without reheating. In the tundish before supplying the molten steel into the tundish, the initial electric resistance between the one electrode 5 and the other electrode 6 is set to 500Ω or more. If the initial electrical resistance is less than 500Ω, sufficient current does not flow in the molten steel passing through the immersion nozzle 4 during casting, and current flows in a short circuit other than the molten steel, causing oxidation of Al in the molten steel on the inner surface of the immersion nozzle. It is not possible to effectively prevent the adherence of objects.

As the form of insulation, the tundish 1 and one electrode 5, the upper nozzle 2 and the refractory of the tundish 1 and the tundish iron skin, the sliding gate 3 and the tundish 1 are connected. A structure in which a refractory having low electric conductivity is sandwiched between the iron skin and the like may be used. Further, an insulating sheet made of glass fiber or the like can be inserted between them. Between the upper nozzle 2, the sliding gate 3 and the immersion nozzle 4, between these and the supporting member, between the layers in the case of a two-layer structure, etc.,
It is preferable to provide an insulating sheet.

More specifically, when the other electrode 6 is arranged by using the immersion nozzle 4 as a refractory having electric conductivity, and when electricity is applied between this immersion nozzle and the molten steel passing through the immersion nozzle, Either the tundish 1 and the one electrode 5, between the immersion nozzle and the gate 3 in contact with the immersion nozzle, or between the immersion nozzle and the holder for holding the immersion nozzle on the sliding gate, or both are electrically connected. It is desirable to electrically insulate. This allows
The immersion nozzle 4 and the tundish 1 main body composed of the tundish lining refractory and the iron skin are also electrically insulated.

Further, the immersion nozzle 4 and the gate 3 are made of refractory material having electric conductivity, and the other electrode is arranged on each of them, and the immersion nozzle 4 and the upper nozzle 2 and the molten steel passing through the inside of the immersion nozzle are formed. When energizing between
Between the tundish 1 and the one electrode 5, between the gate 3 and the tundish body, between the gate 3 and the upper nozzle, and between the gate 3 and a cassette holder that holds the gate on a tundish iron skin or the like. It is desirable to electrically insulate either or both of them.

Further, the immersion nozzle 4, the gate 3 and the upper nozzle 2 are made of a refractory material having electric conductivity, and one electrode is arranged on each of them, so that the immersion nozzle 4 and the gate 3 are provided.
In addition, when electricity is applied between the upper nozzle 2 and the molten steel passing through the immersion nozzle, between the tundish 1 and the one electrode 5, between the tundish body and the immersion nozzle, the gate and the upper nozzle. It is desirable to electrically insulate either or both of them.

Mineral materials used for insulation generally have an electrical resistivity of 1 × 10 ⁵ Ω · m or more at room temperature,
Although it exhibits a sufficient insulating property, when many materials are exposed to a high temperature such as molten steel temperature, ionic conduction occurs, so that the electrical resistivity decreases. Therefore, even at a high temperature such as the molten steel temperature, a refractory with a small decrease in electrical resistivity, for example,
Al ₂ O _3, the insulating sheet made of fibrous insulating refractories, such as SiO _2, or the like can be used coating materials such as these Al ₂ O _3, SiO _2.

As a concrete construction method of these insulating sheets, coating materials, etc., for example, for a gate portion in contact with the immersion nozzle, and a holder portion in contact with the immersion nozzle for holding the immersion nozzle on the slide gate, The insulating sheet may be inserted and sandwiched. that time,
The sandwiching thickness is preferably 1 to 4 mm. Further, it is more desirable to combine the method of applying the coating material with the adhesive to the portion to be insulated. At that time, the thickness of the coating material is 0.2 ~
1.0mm is desirable. Further, as the adhesive, an alumina-based or silica-based adhesive can be used.

The upper limit of the electric resistance at the beginning is ideally infinite, but when considering an apparatus for supplying molten steel from the tundish of an actual continuous casting machine into the mold, it is realistically
The upper limit is 1 × 10 ⁸ Ω.

In the continuous casting method of the present invention, the electric resistance during casting, which is calculated from the current and voltage between the one electrode 5 and the other electrode 6 between the start and the end of casting, is Before supplying the molten steel into the tundish at the end of preheating the tundish before supplying the molten steel into the tundish, or when the tundish once used for casting is used again for casting without preheating. It is desirable to be less than 1/10 of the original electric resistance between one electrode and the other electrode in the tundish of. The reason will be described below.

FIG. 5 is a diagram illustrating changes in electric resistance during casting between one electrode and the other electrode during casting.
The figure shows an example where the initial electrical resistance is 0.7Ω. Although the resistance may change little even after the casting time, that is, the energization time, the resistance of the electric circuit of the current flowing through the molten steel passing through the immersion nozzle is usually large. It is presumed that this is because the surface of the refractory material having electrical conductivity, which is placed in the immersion nozzle, in contact with the molten steel deteriorates with time or a non-conductive substance such as alumina adheres.

The electric resistance during casting is 1/1 of the original electric resistance.
When it becomes 0 or more, current does not flow properly in the molten steel passing through the immersion nozzle, some current flows in the short circuit other than molten steel, and oxides of Al in molten steel adhere to the inner surface of the immersion nozzle. Cannot be prevented. In addition, if the electric resistance during casting becomes significantly higher than the initial electric resistance by more than 1/10, not only will the applied power be wasted, but a lot of current will flow in the short circuit other than molten steel, There is a danger that a minute discharge will occur due to the electric leakage. At that time, there is a case where an electric shock may be caused or a peripheral device may malfunction.

FIG. 6 is a diagram showing the influence of the electric resistance between one electrode and the other electrode on the surface properties of the cold rolled product. The horizontal axis represents the value of the initial electric resistance between one electrode and the other electrode immediately before the start of casting. The vertical axis is the value of the electrical resistance during casting calculated from the current and voltage between one electrode and the other electrode at the end of casting after the start of casting divided by the value of the initial electrical resistance. is there.

The slab was hot-rolled into a steel strip having a thickness of 5 mm, then pickled and cold-rolled to give a steel strip having a thickness of 0.8 mm. Investigate the occurrence of product surface flaws and their occurrence status, and determine the total length of the cut-off length of the portion where product surface flaws are caused by defects in the mold powder, cast iron such as Al oxide, etc. The product defect occurrence rate was calculated by dividing by and displaying in%. The circles in the figure mean that no defects on the product surface due to defects on the surface of the slab such as mold powder on the surface of the slab and oxides of Al in molten steel are generated.

The Δ mark in FIG. 6 indicates that the product defect occurrence rate is 0.
Within 5%, it means that a slight defect on the product surface occurred. The ▲ mark in the figure indicates that the product defect occurrence rate is 1
Within%, it means that defects on the product surface have occurred.
However, if the defect occurrence rate of the product is within 1%, there is no particular problematic defect occurrence situation. In addition, the mark x in the figure means that the product defect occurrence rate exceeds 5%, and the defects on the product surface are remarkably large. By changing the construction method of the insulating part, the initial electric resistance value is changed and the results of the test are shown.

From the result of FIG. 6, the initial electric resistance is 500Ω.
By the above, it can be understood that the occurrence of defects on the product surface can be prevented. Furthermore, if the electrical resistance during casting, which is calculated from the current and voltage between one electrode and the other electrode at the end of casting, is less than 1/10 of the original electrical resistance, a better product surface is obtained. You can see that you can get it. Further, the lower limit of the ratio of the electric resistance during casting to the initial electric resistance is ideally zero, but when considering a device for supplying molten steel from the tundish of an actual continuous casting machine into the mold, In particular, 0.00001 / 10 is the lower limit. 4. A gas blowing portion (not shown) made of a porous refractory may be provided in any of the gas blowing upper nozzle 2, the sliding gate 3, and the immersion nozzle 4. This gas blowing part is used as follows.

In order to prevent Al oxides and the like from adhering to the inner surface of the dipping nozzle 1 when processing molten steel, Al oxides and the like increase in the molten steel depending on the operating conditions such as the converter and RH. Blow with inert gas. Further, in order to prevent the opening failure of the immersion nozzle due to the solidification of the molten steel at the start of casting and to improve the flow of the molten steel in the mold,
Blow with an inert gas.

In this case, any one or two of the upper nozzle 2, the sliding gate 3 and the dipping nozzle 4, and preferably the dipping nozzle 4 is provided with the other electrode 6 and the other electrode 6. It is advisable to provide the gas blowing section in one or two of the missing members. In this way, since the other electrode 6 and the gas blowing portion do not exist in one member, it is possible to prevent the strength of the refractory from lowering.

In the molten steel supply apparatus shown in FIG. 1, the one electrode 5 is provided so as to penetrate the side wall of the tundish 1 so that the tip thereof reaches the internal space of the tundish 1. It may be provided so as to reach the internal space from the upper part of the tundish 1 without penetrating the side wall. Alternatively, a part of the side wall of the tundish 1 may be made of a refractory material having electrical conductivity, and this part may be the one electrode 5.

The upper nozzle 2 or the sliding gate 3 may be made of a refractory material having electrical conductivity, and the upper nozzle 2 or the sliding gate 3 may be provided with one electrode 5. When the upper nozzle 2 is provided with one electrode 5, one or both of the sliding gate 3 and the immersion nozzle 4 are made of a refractory material having electrical conductivity, and the other electrode 6 is provided on one or both of them. To provide.
When one electrode 5 is provided on the sliding gate 3, one or both of the upper nozzle 2 and the dipping nozzle 4 are made of a refractory material having electrical conductivity, and the other electrode 6 is provided on one or both of them. Set up. In either case, an insulator is provided between the member provided with one electrode 5 and the member provided with the other electrode 6. Further, an insulator may be provided between the upper nozzle 2 and the tundish 1 so that the electric current does not flow in the tundish 1. 5. Application of Current and Voltage In the continuous casting method using the molten steel supply device shown in FIG. 1, the molten steel supply device is placed on the mold 9 and the molten steel 8 in the tundish 1 is moved to the upper nozzle 2, the sliding gate 3 and the immersion gate. It is supplied into the mold 9 by the nozzle 4.

At this time, the power supply section 7 is turned on.
The power supply unit 7 is connected to the one electrode 5 and the other electrode 6 by an electric wiring 7a. And one electrode 5 is
The other electrode 6 immersed in the molten steel in the tundish 1
Is provided on the immersion nozzle 4 made of a refractory material having electrical conductivity. Therefore, electricity is supplied between the inner surface of the immersion nozzle 4 and the molten steel passing through the inside of the immersion nozzle 4.

The applied current may be direct current or alternating current. In the case of direct current, the immersion nozzle side may have any positive or negative potential. Further, it may be a pulse wave or a rectangular wave. This energization may be intermittent rather than continuous.

As described above, when an electric current is applied between the inner surface of the immersion nozzle 4 and the molten steel passing through the immersion nozzle 4, the interfacial tension between the inner surface of the immersion nozzle 4 and the molten steel decreases due to the electrocapillary phenomenon described above. Therefore, the force of adhesion of Al oxides in molten steel to the surface of the refractory is reduced, and the immersion nozzle 4
It becomes difficult for Al oxides and the like to adhere to the inner surface of the.

When energized, the current density per surface area of the electrically conductive portion of the refractory material having electrical conductivity is 0.00
It is desirable to set it to 1 to 0.3 amps / cm ² (A / cm ² ).
If it exceeds 0.3 A / cm ² , the effect will be saturated and the refractory will generate heat due to its electrical resistance. Further, when a large current density is applied over a wide area, the power supply unit 7 and the devices such as wiring become large in size, and a large amount of electric power is required. Also
If it is less than 0.001 A / cm ² , the effect of preventing adhesion cannot be obtained. More preferably, it is 0.01 to 0.1 A / cm ² .

The applied voltage between the other electrode 6 and the one electrode 5 is a value determined by the current density, the electric resistance of the refractory, and the electric resistance due to the deposits adhering to the inner surface of the refractory. It is preferable that the voltage is V (V). When the applied voltage is less than 0.5 V, an effective current does not flow from the resistance of the energizing path, and it becomes difficult to detect the applied current and voltage. If the upper limit of the applied voltage is 100V, the required current can be flown by appropriately setting the resistance of the energizing path, but if it exceeds 100V, the risk of electric shock suddenly increases.
Therefore, the more desirable range of the applied voltage is 1 to 60V.

FIG. 7 shows that when the immersion nozzle 4 is made of a refractory material having electrical conductivity, the other electrode 6 is embedded in the immersion nozzle 4 and continuously cast under the same conditions as in Example 1 described later. FIG. 6 is a diagram showing a relationship between the thickness of a deposit such as an Al oxide deposited on the inner surface of the immersion nozzle 4 and the applied voltage between the other electrode 6 and one electrode 5. In FIG. 7, the current paths and the current densities are increased by the positive correlation with the voltage by making the energization paths the same and making the contact areas of the molten steel and the refractory material having conductivity the same.

As is clear from the figure, when the argon gas is not flown (marked with ● in the figure), the thickness of the deposit is about 13 mm when the potential is 0 (zero), but the potential is +1 V or -1.
Assuming V, the thickness of the deposit is reduced to about 8 mm. When the potential is +5 V or -5 V, the thickness of the adhered amount is reduced to about 4 mm. The thickness of this deposit is 0
Thus, it is thinner than 5 mm when the flow rate of the argon gas is set to 20 liters (Nl) / min (marked with a circle in the figure). In addition, the potential is +
If the voltage is 20V or -20V, the thickness of the deposit is 1
It is reduced to about mm. In addition, in the figure, although there is no clear difference, when the immersion nozzle 4 is set to a negative (-) potential, it is attached to the inner surface of the immersion nozzle 4 compared to when it is set to a positive (+) potential. The thickness of the deposited substance tends to be thin. 6. Making the immersion nozzle side a negative potential If the immersion nozzle 4 is made to have a negative potential and a current is applied to the molten steel as a negative potential, the thickness of the deposit attached to the inner surface of the immersion nozzle 4 becomes thinner. Tend. This is for the following reason.

When a current is applied, for example, in a refractory material containing carbon such as alumina graphite, electron conduction in carbon is the main component, but polarization occurs in the oxide. This polarization is the cause of the above-mentioned change in surface tension, but in the oxide forming the refractory, the reactions shown by the following formulas (a) to (c) occur.

Si ⁴⁺ + 4e ⁻ = Si (a) Al ³⁺ + 3e ⁻ = Al (b) O ² − = O + 2e ⁻ (c) At this time, a refractory having electrical conductivity is negative. At the potential of, the reactions of (a) and (b) proceed to the right, but the reaction of (c) does not proceed. For this reason, oxygen, which is a source of alumina, is not generated, and adhesion to the inner surface of the nozzle can be prevented.

When a refractory having electrical conductivity is set to a negative potential and a direct current is passed between the refractory and molten steel, the interfacial tension is lowered, and as a result,
The reaction of the equation (c) is suppressed, and it is possible to prevent the oxides of Al in molten steel from adhering to the surface of the refractory.

When a direct current is applied with this refractory as a positive potential, the reaction of the above formula (c) is promoted even if the interfacial tension is lowered, so that Al oxides or the like are contained in the refractory. The effect of preventing adhesion to the surface is small. Further, when an alternating current is passed between the electrically conductive refractory and the molten steel, promotion and suppression of the reaction of the above formula (c) will occur alternately, such as oxides of Al in molten steel. Has a small effect of preventing adherence to the surface of the refractory. Therefore, it is desirable to energize the direct current with the immersion nozzle 4 having a negative (-) potential.

As described above, the molten steel 8 in the tundish 1 is supplied into the mold 9 while energizing the molten steel 8 passing through the inner surface of the immersion nozzle 2 and the inside thereof. On the upper surface of the molten steel in the mold 9, heat retention and oxidation prevention of the molten steel in the mold 9,
A mold powder 11 is added to lubricate the mold 9 and the solidified shell 10. The molten steel 8 supplied into the mold 9 forms a solidified shell 10 from the surface in contact with the mold 9, and then is drawn into a cast piece by a drawing device (not shown).

When the molten steel 8 passes through the immersion nozzle 4,
Since electric current is applied to the inner surface of the immersion nozzle 4 to provide a potential difference, Al oxide or the like does not adhere to the inner surface of the immersion nozzle 4. Further, since an inert gas such as argon gas is not blown into the molten steel, the cast piece does not have a bubble defect.

In the continuous casting method of the present invention, the upper nozzle 2 is provided with a molten steel supply section provided with a gas blowing section, and the upper nozzle 2 passes through the upper nozzle 2 to the extent that no bubble defects are generated in the surface layer of the slab. It is desirable to blow an inert gas into the molten steel. When the bubbles of the inert gas float in the molten steel in the mold, the oxides in the molten steel float in the molten steel together with the bubbles,
It is removed to the outside of the molten steel system by being trapped by the molten mold powder on the surface of the molten steel. Therefore, the cleanliness of the slab is improved, and a product with good cleanliness can be obtained. that time,
The flow rate of the inert gas blown depends on the slab size,
It is desirable to set 2 to 10 liters (Nl) / min.

As described above, the molten steel feeding apparatus of the present invention is
It is most suitable for continuous casting of deoxidized molten steel. However, the molten steel supply device of the present invention is not limited to this, further, elements that cause the blockage of the immersion nozzle and the like, for example, zirconium, calcium, even in the continuous casting of a metal containing a rare earth metal, It is possible to prevent oxides of these elements from adhering to the inner surface of the immersion nozzle.

[0103]

[Example 1] Using a vertical bending type continuous casting machine
270 mm thick, 160 width wide from A and B molten steel deoxidized with Al
A 0 mm slab was produced. Table 1 shows the chemical composition of the molten steel.

[0104]

[Table 1]

In the vertical bending type continuous casting machine, one or more of the upper nozzle, the sliding gate, and the dipping nozzle are made of a refractory material having electrical conductivity, and the other electrode is attached to the member made of the refractory material having electrical conductivity. What was equipped with the molten steel supply device in which was embedded was used. In the test, a gas injection part was installed on the upper plate or the upper nozzle part of the sliding gate, and 3 to 5 Nl / min required for opening holes at the beginning of casting.
Blow a small amount of gas. With this level of blowing, no pinholes were generated on the surface of the slab, and almost no gas gushes out in the mold, so almost all the gas floated to the tundish side without being introduced into the mold. The upper plate of the sliding gate was a conventional one without electrodes, but in some tests, it was made of a refractory material having electrical conductivity and connected to the other electrode. The tundish used has a normal box shape with a capacity of about 85t.
Met.

The dipping nozzle has an inner diameter of 90 mm and a downward angle of 35 °.
Which has two discharge holes. Further, the member in which the other electrode was embedded was made up of 22% by mass of graphite, SiO ₂
Is a refractory material having an electric conductivity of alumina graphite which contains 12% of Al, and the balance is alumina and impurities.

A sheet made of fibers of alumina and silica or a refractory material of alumina was interposed between the member in which the other electrode was buried and the adjacent member for insulation.
One electrode was dipped from the surface of molten steel contained in a tundish as alumina graphite. The other electrode was made of graphite or steel, and the installation position was variously changed.

At the time of continuous casting, molten steel of about 270 t per heat was cast continuously for 6 heats. At this time, the superheat degree of the molten steel in the tundish is 20 to 30 ° C, and the casting speed is 1.5 to 1.8.
m / min. Further, alternating current or direct current was applied between one electrode and the other electrode to give a potential difference of 0 to 20V. The current at this time is in the range of 0 to 120A. At that time, the current value a and the surface area b of the conductive portion of the refractory inner surface facing the molten steel which is joined to the other electrode are changed variously to obtain the current density (A / c
A change test of m ² ) was performed.

Current density (A / cm ² ) = a / b (d) Here, a: current value (A) b: a refractory that is joined to the other electrode and faces the molten steel, and has conductivity Surface area (cm ² ) of the inner surface of the portion When a direct current was applied, the other electrode side was set to a positive or negative potential. In some tests, no current was applied between one electrode and the other electrode. Table 2 shows these test conditions.

[0110]

[Table 2]

After the above continuous casting is completed, the upper nozzle,
The sliding gate and the immersion nozzle were collected, and these were longitudinally cut to measure the thickness of the adhered amount on the inner surface. The thickness of the adhered amount on the inner surface is the average value of the inner diameters measured at two positions in the circumferential direction at three positions in the length direction of the upper nozzle, the sliding gate, and the immersion nozzle where the other electrode is provided. 1/2 of the value obtained by subtracting from the inner diameter before use
It is represented by.

Next, using the obtained slab as a material, 4 to 6
After hot rolling into steel strip with a thickness of mm, then pickling, 0.8
Cold rolling was performed on steel strips with a thickness of ~ 1.2 mm, and the surface flaw occurrence rate of the steel strips was investigated. The surface flaw occurrence rate of a steel strip is visually checked for the occurrence of surface flaws on the steel strip, and the portion where surface flaws occur is cut by that length, and the total length of the cuts is the cold rolling length. It was removed and expressed as the rate of surface defects. These results are shown in Table 2, and the following can be seen from the results in Table 2.

In Test No. 1, since no electric potential was applied and Ar gas was blown in at a small amount of 5 Nl / min for opening holes at the initial stage of casting, the deposit thickness on the inner surface of the immersion nozzle was as thick as 13.4 mm. The occurrence rate of surface flaws is as high as 9.6%. next,
In Test No. 2, no potential was applied, but Ar gas was 20 Nl / mi
Since a large amount of n was blown in, the thickness of the deposit on the inner surface of the immersion nozzle was 5.4 mm, which was thinner than in Test No. 1, and the occurrence rate of surface defects was as low as 3.8%.

In Test Nos. 3 to 8, + 2V, + 5V, + 20V, -2V,-were applied to the immersion nozzle in which the other electrode was embedded.
Since a direct current was applied by applying a potential of 5 V or -20 V, both the thickness of the deposit on the inner surface of the refractory (dipping nozzle) and the occurrence rate of surface flaws were lower than Test No. 1. Especially when the potential is + 5V, + 20V, -5V, or -20V,
Both the thickness of the deposit on the inner surface of the refractory (immersion nozzle) and the occurrence rate of surface flaws are superior to those of Test No.2.

In Test Nos. 9 and 10, a direct current was applied by applying a potential of +2 V or -2 V to the immersion nozzle in which the other electrode was embedded, and 5 Nl / min of Ar gas was blown directly into the immersion nozzle. Therefore, compared to Test No. 3 or 6 in which the electric potential was applied under the same conditions and Ar gas was not blown in, the thickness of the deposit on the inner surface of the refractory material (immersion nozzle) was smaller, but the occurrence rate of surface defects was It was equivalent. Further, the gas blowing portion is worn. By applying an electric current to the gas blowing part, the refractory of the nozzle was brought into the slab, and because Ar gas was blown directly into the immersion nozzle, the fact that Ar gas was introduced into the mold was a defect. Responsible.

In Test No. 11, since the alternating current was applied by applying a potential of 5 V to the immersion nozzle having the other electrode embedded, the thickness of the deposit on the inner surface of the refractory (immersion nozzle) and the occurrence rate of surface flaws were as follows. Test Nos. 4 and 7 in which direct current was applied at the same potential
Was equivalent to.

In test No. 12, since the other electrode was embedded in the sliding gate which was the Ar gas blowing part, and a potential of +2 V was applied to the sliding gate and a direct current was applied, the sliding gate was worn and casting was not possible. There wasn't. In Test Nos. 9 and 10 described above, embedding the other electrode in the immersion nozzle did not cause any problem, but wear of the sliding gate portion causes suspension of casting.

In Test Nos. 13 to 14, since the other electrode was embedded in a sliding gate having no Ar gas blowing part, and a potential of +2 V or -5 V was applied to the sliding gate to apply a direct current, refractory (sliding The thickness of the deposit on the inner surface of the gate is thin and good, but the occurrence rate of surface defects is inferior to that when the nozzle is energized.

In Test No. 15, since the other electrode was embedded in the upper nozzle and a DC voltage was applied by applying a potential of -5 V to the upper nozzle, the deposit on the inner surface of the refractory (upper nozzle) was thin and good. However, the occurrence rate of surface defects is inferior to that when the nozzle is energized.

In Test Nos. 16 to 17, the other electrode was embedded in the upper nozzle and the dipping nozzle, and +2 V or -5 V was applied to these electrodes.
Since a direct current was applied by applying the potential of No. 2, the thickness of the deposit on the inner surface of the refractory in which the other electrode was embedded and the rate of occurrence of surface defects were good.

Test Nos. 18 to 27 are the results of performing the same test with steel type B (extremely low carbon steel). The extra-low carbon steel has an increased amount of deposits, and on the other hand, the required level of surface properties of the product is high, so that the defect generation rate tends to deteriorate. Test No. 22 and N
o.26 reduces the current density to 0.0009 A / cm ² ,
Although the potential was set to V or -0.6 V, almost no anti-adhesion effect was observed, and a high surface flaw generation rate was obtained.

Test No. 21 with current density of 0.006 A / cm ²
And No. 25, the anti-adhesion effect is recognized. Further effects were obtained in Test Nos. 19, 20, 23 and 24 in which the current density was further increased. In addition, negatively applied test No. 23-26
Exhibited a relatively good anti-adhesion effect as compared with Nos. 19 to 22 which were positively applied.

Example 2 By the same method as in Example 1, a slab having a thickness of 270 mm and a width of 1200 to 1600 mm was cast at a speed of 1.4 to 1.7 m / min. However, the material of the immersion nozzle is mass%
And contains 31% graphite and 14% SiO ₂ and the balance is almost Al ₂ O.
Of _3, and an alumina graphite substance having electrical conductivity at a temperature of the molten steel. One electrode made of carbon steel was attached to the outer peripheral portion of this immersion nozzle. The other electrode made of alumina graphite was immersed in the molten steel from the surface of the molten steel in the tundish.

Between the immersion nozzle and the sliding gate in contact with the immersion nozzle, and between the immersion nozzle and the holder for holding the immersion nozzle on the sliding gate, a refractory material containing Al ₂ O ₃ and SiO ₂ as main components was used. The sheet made of the above fiber and / or an antioxidant containing SiO ₂ as a main component was applied to electrically insulate the sheet. At that time, the thickness of the sheet and the coating material was changed and tested.

Before the casting test, the tundish, the upper nozzle, the sliding gate, the dipping nozzle, etc. were preheated for about 3 hours using ordinary combustion gas, and the surface temperature of the tundish lined refractory material was 1000 to 1200 ° C. And Immediately before ending preheating, the initial electrical resistance between one electrode and the other was measured.

In the casting test, molten steel of about 270 tons of 1 heat was continuously cast for 6 heats, and from the start to the end of casting,
A current or a voltage was applied between one electrode and the other electrode. At that time, the current is 10 to 100 A and the voltage is 3 to 8 A.
The value was 0V. From these current and voltage, the electric resistance during casting between one electrode and the other electrode was determined.

In addition, from the porous refractory placed in the sliding gate during casting to the molten steel passing through the inside.
Ar gas was blown in at a flow rate of 2 to 5 liters (Nl) / minute. It was previously confirmed that this blowing flow rate was not an amount that would cause a bubble defect on the surface of the slab.

After the completion of casting, the immersion nozzle was recovered and cut longitudinally, and the presence or absence of deposits inside and the thickness of the deposits were examined. The slabs obtained in the 2nd and 6th heats were hot-rolled into a steel strip having a thickness of 4 to 6 mm, then pickled and then cold-rolled to obtain a steel strip having a thickness of 1.6 to 1.2 mm. And The occurrence rate of product defects was determined by investigating the occurrence of product surface defects and the occurrence status. The defect rate of this product is
It was determined by dividing the total cut-off length of the portion where the product surface flaw was caused by the defects of the slab, such as the oxide of Al, by the total length of the steel strip and expressing it as a percentage. Table 3 shows the test conditions and test results.

[0129]

[Table 3]

In the test No. 28, the thickness of the refractory fiber made of the refractory material was 2.5 m between the dipping nozzle and the sliding gate.
A sheet of m was inserted, and a SiO ₂ -based antioxidant was applied to a thickness of 0.2 mm between the immersion nozzle and its holder. Immediately before ending the tundish preheating, the initial electrical resistance between one electrode and the other is 600 Ω.
Met. This value is within the range defined by the present invention. The electric resistance during casting in the sixth heat immediately before the end of casting was 72Ω. The value obtained by dividing the electric resistance during casting by the initial electric resistance (hereinafter referred to as the electric resistance ratio) is 1.2 /
The value was 10, which was slightly outside the range of desirable conditions. In Test No. 28, the thickness of the deposit on the dipping nozzle after casting was as small as 5 mm, which was a good result. In addition, the product defect occurrence rates of the second heat and sixth heat cast slabs were 0.6% and 0.9%, respectively, which were reasonably good results.

In Test No. 29, a thickness of 2.5 m made of refractory fiber was provided between the dipping nozzle and the sliding gate.
A sheet of m was inserted, and a SiO ₂ -based antioxidant was applied to a thickness of 0.4 mm between the immersion nozzle and its holder. Immediately before ending the tundish preheating, the initial electrical resistance between one electrode and the other is 600 Ω.
Met. This value is within the range defined by the present invention. The electric resistance during casting in the sixth heat immediately before the end of casting was 58Ω. The ratio of electric resistance during this casting is 0.97
It was / 10, which was within the range of desirable conditions. Test No. 29
Then, the thickness of the deposit on the dipping nozzle after casting was as small as 4 mm, which was a good result. In addition, the product flaw occurrence rate using the slab of the second heat and the sixth heat is 0.3, respectively.
% And 0.5%, which is a small and good result.

In Test No. 30, a sheet having a thickness of 4.0 mm was inserted between the immersion nozzle and the sliding gate, and a thickness of 1.0 m was provided between the immersion nozzle and its holder.
Insert a sheet of m and add antioxidant with a thickness of 0.5 mm
Was applied. Immediately before ending the preheating of the tundish, the initial electric resistance between the one electrode and the other electrode was 1200Ω. This value is a value within the range defined by the present invention. Compared with test No. 29, the initial electric resistance doubled because the thickness of the sheet between the dipping nozzle and the sliding gate was thicker and between the dipping nozzle and its holder. In addition to the sheet, an antioxidant was applied. The electrical resistance during casting in the sixth heat immediately before the casting was 8Ω. Therefore, the electric resistance ratio was 0.07 / 10, which was within the range of desirable conditions. In Test No. 30, the thickness of the deposit on the dipping nozzle after casting was 4 mm, which was a good result. In addition, the product defect occurrence rates using the second heat and sixth heat slabs were 0.3% and 0.4%, respectively, which were favorable results.

In the test No. 31, the insulation construction method is the test No. 31.
Same as 30. Immediately before ending the preheating of the tundish, the initial electric resistance between the one electrode and the other electrode was 1050Ω. In the sixth heat, the electric resistance during casting immediately before the end of casting was 0.5Ω, and the increase in resistance during casting was small. Therefore, the electrical resistance ratio was 0.005 / 10, which was within the range of desirable conditions. In Test No. 31, the thickness of the deposit on the dipping nozzle after casting was 2 mm, which was a good result. In addition, the product defect occurrence rates in the case of using the slabs of the second heat and the sixth heat were as small as 0.3%, respectively, which were favorable results.

In Test No. 32, the thickness of the sheet between the immersion nozzle and the sliding gate was 2.0 mm, and an alumina plate having a thickness of 3 mm was sandwiched. The thickness of the sheet between the dipping nozzle and its holder was 1.8 mm, and the thickness of the antioxidant was 0.7 mm. The initial electrical resistance between the one electrode and the other electrode was 380 × 10 ³ Ω immediately before the end of the preheating of the tundish. This value is within the range defined by the present invention. Since the thickness of the sheet and the coating material was increased, the initial electric resistance became an extremely large value. The electrical resistance during casting in the sixth heat immediately before the casting was 13Ω. Therefore, the electrical resistance ratio was 0.0003 / 10, which was within the range of desirable conditions. In Test No. 32, the thickness of the deposit on the dipping nozzle after casting was 1 mm, which was extremely small, which was the best result. In addition, the product flaw occurrence rates of the second heat and sixth heat cast slabs were 0.1% and 0.2%, respectively, which were extremely small and good results.

In Test No. 33, the sheet thickness was 2.0 mm and the coating material thickness was 0.6 mm. Immediately before ending the preheating of the tundish, the initial electric resistance between the one electrode and the other electrode was 420Ω. This value was a small value outside the conditions specified in the present invention. Also,
The electrical resistance during casting in the sixth heat immediately before the end of casting was 64Ω. Therefore, the ratio of electrical resistance rises to 1.5 / 10,
Out of the desired conditions. In Test No. 33, the thickness of the deposit on the immersion nozzle after casting was 7 mm, which was slightly thick. Also, 2
Product flaw rates using the slabs of the 6th and 6th heats were 0.8% and 7.9%, respectively, and the results of the 6th heat were particularly bad.

In Test No. 34, without using the sheet made of the refractory fiber, both the immersion nozzle and the sliding gate, and between the immersion nozzle and the holder thereof, the SiO ₂ -based antioxidant was used. Was applied at a thickness of 0.7 mm and 0.5 mm. The initial electrical resistance between one electrode and the other immediately before ending the tundish preheating is
It was 30Ω. This value was a significantly small value outside the conditions specified in the present invention. The electrical resistance of the sixth heat immediately before casting was 32Ω. Therefore, the ratio of electric resistance increased to 10.6 / 10, which was a large value outside the desirable conditions. In Test No. 34, the thickness of the deposit on the immersion nozzle after casting was 11 mm, which was considerably large. In addition, the product flaw occurrence rates using the slabs of the second heat and the sixth heat were 8.4% and 12.3%, respectively, which were both bad results.

In test No. 35, no electrical insulation was performed and no electricity was supplied. The thickness of the deposit on the dipping nozzle after casting was 13 mm, which was the thickest and had a bad result. In addition, the product flaw occurrence rates using the second heat and sixth heat cast pieces as raw materials were 9.8% and 11.8%, respectively.

Example 3 By the same method as in Example 1, a slab having a thickness of 270 mm and a width of 1000 mm was produced. The vertical bending type continuous casting machine used was the molten steel supply device shown in FIG. 1, in which the upper plate of the sliding gate was provided with the molten steel supply device having a gas blowing part made of a porous refractory.

At the time of continuous casting, the potential difference between one electrode and the immersion nozzle was set to 1.5 to 25 V, and a direct current or an alternating current was applied between them. When applying a direct current, the potential on the immersion nozzle side was set to positive or negative. In some tests, no current was applied between one electrode and the dipping nozzle. Further, in some tests, Ar gas was blown into the molten steel at a flow rate of 20 liters (Nl) / minute from a gas blowing section provided in the sliding gate.

After the casting, the immersion nozzle was recovered and cut longitudinally, and the presence or absence of deposits in the vicinity of the discharge holes and the deposit thickness were examined. Further, the obtained slab was cold-rolled into a steel strip having a thickness of 0.8 to 1.2 mm by the same method as in Example 1, and the surface flaw occurrence rate was investigated by the same method as in Example 1. Table 4 shows the test conditions and test results.

[0141]

[Table 4]

In test No. 36, since the direct current was applied with the positive potential on the dipping nozzle side and the current density of 0.17 A / cm ² , the thickness of the deposit on the inner surface of the dipping nozzle was 3.0 mm and the surface defect rate was It was 1.8%.

In Test No. 37, the immersion nozzle side was set to a negative potential, and the other conditions were the same as in Test No. 36. As a result, the thickness of deposits on the inner surface of the immersion nozzle was 1.3 mm and the occurrence rate of surface defects was 0.2%, and both the thickness of deposits on the inner surface of the immersion nozzle and the occurrence rate of surface defects were superior to those of Test No. 36. ing.

In test No. 38, since a direct current was applied with a positive potential on the dipping nozzle side and a current density of 0.092 A / cm ² , the thickness of the deposit on the inner surface of the dipping nozzle was 3.5 mm, and the occurrence rate of surface defects was It was 2.1%.

In Test No. 39, the immersion nozzle side was set to a negative potential and the other conditions were the same as in Test No. 38. However, the thickness of the deposit on the inner surface of the immersion nozzle was 1.8 mm, and the surface flaw occurrence rate was 0.3. %, Which is superior to the test No. 38 in both the thickness of deposits on the inner surface of the immersion nozzle and the surface flaw occurrence rate.

In Test No. 40, the current density was 0.17 A / cm ² , alternating current was passed, and the other conditions were the same as those in Test No. 36. The surface flaw ratio was 3.0 mm and the surface flaw occurrence rate was 1.8%. Both the thickness of deposits on the inner surface of the immersion nozzle and the surface flaw occurrence rate were similar to those of Test No. 36.

In test No. 41, Ar gas was blown into the molten steel from the sliding gate at a flow rate of 20 liters (Nl) / min without energization. The thickness was 5.0 mm and the surface flaw generation rate was 2.3%. Both the thickness of the deposit on the inner surface of the immersion nozzle and the surface flaw generation rate were relatively poor results.

In Test No. 42, no current was passed and Ar gas was not blown into the molten steel from the sliding gate, so that the immersion nozzle was clogged during casting and casting was performed during the third heat. I had no choice but to cancel. A 13 mm-thick deposit adhered to the vicinity of the discharge hole of the immersion nozzle after casting, and the surface flaw generation rate was 5.1%.

[0149]

According to the molten steel supply apparatus of the present invention, Al in molten steel is formed on the inner surfaces of the upper nozzle, the flow rate control mechanism and the immersion nozzle.
It is possible to stably prevent the oxide and the like from adhering. Furthermore, by applying the continuous casting method using this molten steel supply device, the product using the obtained slab as a material, mold powder, Al oxide, the occurrence of defects due to defects in the slab such as bubbles Can be prevented. Moreover, it is possible to effectively prevent the immersion nozzle from being blocked during continuous casting.

[Brief description of drawings]

FIG. 1 is a vertical sectional view schematically showing an example of a molten steel supply unit of the present invention.

FIG. 2 is a vertical cross-sectional view showing another example in which the other electrode is embedded in the immersion nozzle.

FIG. 3 is a front view showing an example in which the other electrode is attached to the outer surface of the immersion nozzle.

FIG. 4 is a front view showing another example in which the other electrode is attached to the outer surface of the immersion nozzle.

FIG. 5 is a diagram illustrating a change in electric resistance during casting between one electrode and another electrode during casting.

FIG. 6 is a diagram showing the influence of the electric resistance between one electrode and the other electrode on the surface properties of a cold rolled product.

FIG. 7: Adhesion to inner surface of immersion nozzle in continuous casting
FIG. 3 is a diagram showing the relationship between the thickness of deposits such as Al oxides and the applied voltage between the other electrode and one electrode.

[Explanation of symbols]

1: Tundish, 2: Upper nozzle, 3: Sliding gate (flow rate control mechanism), 4: Immersion nozzle, 5: One electrode, 6: Other electrode 7: Power supply part, 8: Molten steel, 9: Mold, 10: Solidified shell, 1
1: Mold powder.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B22D 41/54 B22D 41/54 41/58 41/58 C04B 35/101 C04B 35/10 F (72) Invention Shoji Hara, 4-53-3 Kitahama, Chuo-ku, Osaka-shi, Osaka Prefecture Sumitomo Metal Industries, Ltd. (72) Inventor Masayuki Kawamoto 4-53, Kitahama, Chuo-ku, Osaka City, Osaka (72) ) Inventor Toshihiko Murakami 4-53-3 Kitahama, Chuo-ku, Osaka City, Osaka Prefecture F-term within Sumitomo Metal Industries, Ltd. (reference) 4E004 FA01 FB10 HA01 HA02 4E014 DA03 DB01 DB03 4G030 AA36 AA60 BA02 BA30

Claims (11)

[Claims] 1. A tundish for containing molten steel, an upper nozzle provided at the bottom of the tundish, a flow rate control mechanism for controlling a flow rate of supplying the stored molten steel to a mold, and a flow of the supplied molten steel. A molten steel supply device comprising an immersion nozzle, which is provided with a pair of electrodes and a power supply section connected to these electrodes, and the inner surface of any one of the upper nozzle, the flow rate control mechanism and the immersion nozzle, which is in contact with the molten steel, has a melting point of steel or more. It is made of a refractory material having electrical conductivity, and one electrode of the pair of electrodes reaches the internal space of any one of the tundish, the upper nozzle, the flow rate control mechanism and the immersion nozzle so as to come into contact with the molten steel. The apparatus for supplying molten steel used in continuous casting, characterized in that the other electrode is provided in a portion constituted by the refractory material having electrical conductivity. 2. The continuous casting according to claim 1, wherein the refractory material having electrical conductivity above the melting point of the steel has an electric conductivity of 1 × 10 ³ S / m or above at the melting point of the steel. Molten steel feeding device used. 3. A molten steel supply apparatus used for continuous casting according to claim 1 or 2, wherein the refractory material having electrical conductivity above the melting point of the steel is an alumina graphite material. 4. An insulator is provided between one electrode and the other electrode.
A molten steel supply device used for continuous casting according to any one of 1. 5. The continuous according to claim 1, wherein one or more of the upper nozzle not provided with an electrode, the flow rate control mechanism and the immersion nozzle is provided with a gas blowing section. Molten steel supply device used for casting. 6. A molten steel contained in a tundish is supplied to a mold by using the molten steel supply apparatus according to claim 1, and an upper nozzle provided with the other electrode of a pair of electrodes, A continuous casting method characterized in that an electric current is applied between an inner surface of a flow rate control mechanism and an immersion nozzle and molten steel passing through the inside. 7. Preheating of the tundish before supplying the molten steel into the tundish when the molten steel contained in the tundish is supplied to the mold by using the molten steel supply device according to any one of claims 1 to 5. At the end, or when the tundish once used for casting is used again for casting without preheating, before supplying molten steel into the tundish, the electrical resistance between the one electrode and the other electrode is Is 500 Ω or more, a continuous casting method. 8. An electric resistance obtained from the current and voltage applied to the one electrode and the other electrode between the start and the end of casting before the molten steel is supplied into the tundish. At the end of preheating of the tundish, or when the tundish once used for casting is used again for casting without being preheated, before supplying molten steel into the tundish, one electrode and the other of the above The continuous casting method according to claim 7, wherein the electrical resistance between the electrode and the electrode is less than 1/10. 9. The applied current density is 0.001 A / cm ² or more,
The continuous casting method according to claim 6, wherein an electric current is applied so that the electric current is less than 3 A / cm ² . 10. The continuous casting method according to claim 6, wherein the applied voltage is 0.5 V or more and 100 V or less. 11. When supplying molten steel stored in a tundish to a mold using the molten steel supply apparatus according to any one of claims 1 to 5, at least the immersion nozzle has electrical conductivity at a melting point of steel or higher. It is made of a refractory and is provided with another electrode, and the immersion nozzle side is set to a negative potential, and a direct current is passed between the immersion nozzle and the molten steel passing through the immersion nozzle to prevent the immersion nozzle from blocking. A continuous casting method characterized by the above.