JPH0852549A - Production of cast slab having excellent surface characteristic - Google Patents

Abstract

PURPOSE:To provide a method of producing cast slab having excellent surface characteristic by raising the temp. of molten metal at a meniscus part and also, rising this flowing speed. CONSTITUTION:In the method for continuously producing the cast slab by supplying the molten metal into a mold 10 having square cross section from an immersion nozzle 12 having spouting holes 11 at both sides of the right and the left parts, static magnetic field 13 having almost uniform magnetic flux density is generated so as to extend to the whole width direction in the mold 10 at little lower position from the immersion nozzle 12. Further, the spouting holes 11 of the immersion nozzle 12 is directed from the horizontal direction to 15 deg. angle upward. By this method, the molten steel spouted from the nozzle 12 is effectively braked.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a slab having excellent surface properties by increasing the molten steel temperature and the flow velocity of a meniscus in continuous casting of ordinary steel, stainless steel and the like.

[0002]

2. Description of the Related Art In continuous casting of ordinary steel and stainless steel, the molten metal stored in a tundish is guided to a continuous casting mold through an immersion nozzle connected to the bottom of the tundish, and the slab is continuously cast from the bottom. It is being manufactured. The molten metal injected from the immersion nozzle into the mold contains a large number of bubbles and inclusions, and if these inclusions or bubbles enter the slab, it becomes a defect. In the publication, a method for stirring molten metal in a continuous casting mold is proposed, in which the flow of molten metal injected from an immersion nozzle is braked to prevent the inclusions in the molten metal from penetrating deep into the mold. Has been done.
Further, in Japanese Patent Application Laid-Open No. 3-142049, a pair of magnetic poles is arranged above and below each back surface of the opposing side wall of the mold, and the lower magnetic pole suppresses the downward flow due to the discharge flow from the immersion nozzle. A continuous casting method of steel using a static magnetic field has been proposed in which the penetration of inclusions and the entrainment of powder from the meniscus portion are suppressed by reducing the molten metal flow rate in the meniscus portion due to the reversal flow at the magnetic poles. And, JP-A-4-
In Japanese Patent No. 41058, a device for controlling the flow of molten metal in a mold is provided which prevents the intrusion of inclusions due to the discharge flow by providing a static magnetic field in which the magnetic field is oriented in the casting direction at the discharge port position of the immersion nozzle in the mold. Proposed.

[0003]

However, the method described in the above publication is aimed mainly at suppressing the flow of the molten metal injected from the dipping nozzle into the mold to suppress the intrusion of inclusions and the reduction of powder entrainment. However, a sufficient effect cannot be obtained for increasing the flow velocity of the molten metal in the meniscus portion and increasing the temperature of the molten metal. Therefore, as shown in FIG. 4, the present inventor generates a static magnetic field 52 having a substantially uniform magnetic flux density that spreads in the entire width direction in a mold 51 at a position slightly lower than the immersion nozzle 50, thereby applying a brake to the descending molten metal. Effectively for increasing the flow velocity of the molten metal in the meniscus portion 53 and suppressing the lowering of the temperature of the molten metal from the tundish temperature to float and separate inclusions contained in the molten metal and prevent the inclusion of powder. A working casting method was developed. However, when the velocity of the molten metal ejected from the immersion nozzle 50 is high and the magnitude of the magnetic field is large, an MHD counterflow 55 is generated facing the molten metal flow 54 ejected from the immersion nozzle 50, and is included in the molten metal. The problem was that small bubbles of argon gas gathered on the center side and adhered to the side surface of the mold 51 and solidified as they were, and pinholes were likely to occur. Further, when the temperature of the molten metal in the meniscus portion 53 is low because the discharge angle of the molten metal of the immersion nozzle 50 is downward as shown in FIG. 5, the tip of the solidification shell 56 grows abnormally, Oscillation marks were disturbed on the slab, and rolling defects (heage) were sometimes generated. In the case of stainless steel, the above defects are prominently manifested as surface defects, but they are also problems that occur in the casting of ordinary steel. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing a cast slab having excellent surface properties by increasing the temperature of the molten metal in the meniscus portion and increasing the flow velocity thereof.

[0004]

A method according to the above-mentioned object.
The method for producing a slab having excellent surface properties described above is a method for continuously producing a slab by supplying molten metal from a dipping nozzle having discharge ports on the left and right sides of a square-shaped mold, and slightly below the dipping nozzle. A static magnetic field having a substantially uniform magnetic flux density that spreads in the entire width direction is generated in the mold at a position, and the discharge port of the immersion nozzle is directed upward from horizontal to 15 degrees. The method for producing a cast slab having excellent surface properties according to claim 2 is the method according to claim 1, wherein the static magnetic field has an upper end 200 to 80 below the meniscus portion.
It is configured to be at a position of 0 mm. In the method for producing a cast slab having excellent surface properties according to claim 1 or 2, it is preferable that the static magnetic field has a magnetic flux density of 0.1 to 1T.

[0005]

In the method for producing a slab having excellent surface properties according to claims 1 and 2, a static magnetic field having a substantially uniform magnetic flux density which spreads in the entire width direction is generated in the mold slightly below the discharge port of the immersion nozzle. As a result, a brake zone is provided slightly below the discharge port of the immersion nozzle, whereby the molten metal discharged from the immersion nozzle spreads from the horizontal direction to a slightly upper direction and rises along the side wall. At the meniscus portion, the flow velocity of the molten metal flowing inward from both sides increases. As a result, the main part of the molten metal discharged from the immersion nozzle flows only in the upper part of the brake zone, and it is difficult for it to flow into the cooling zone below, so the temperature of the molten metal is high, which makes it easier for the inclusions to float and separate, The thickness of the molten layer is enlarged, and the generation of slag bear is prevented. Moreover, since the flow velocity of the molten metal is high, the temperature of the molten metal becomes uniform and abnormal growth of the solidified shell is suppressed. Further, since the angle of the outlet of the immersion nozzle is in the range of 15 degrees upward from the horizontal, the downflow is reduced, which reduces the MHD counterflow generated by the static magnetic field in the lower part, resulting in the formation of bubbles in the molten metal. I lose my concentration. Then, as shown in FIG. 2, powder entrapment increases when the discharge port of the immersion nozzle exceeds 15 degrees upward. Particularly, in the method for manufacturing a cast slab having excellent surface properties according to claim 2, the meniscus portion has an upper end of the static magnetic field of 200 to 800 mm. This is because, as shown in FIG. 3, if the size is smaller than 200 mm, the volume confined by the static magnetic field decreases, so that powder entrapment easily occurs, and if it exceeds 800 mm, the volume confined by the static magnetic field is too large. This is because the deviation becomes large and the effectiveness of providing the static magnetic field cannot be enjoyed.

[0006]

Embodiments of the present invention will now be described with reference to the accompanying drawings to provide an understanding of the present invention. Here, FIG. 1 is a schematic explanatory view of a method for producing a cast product having excellent surface properties according to an embodiment of the present invention.

FIG. 1 shows a method for producing a stainless cast slab having excellent surface properties according to an embodiment of the present invention. As shown in the figure, a continuous casting mold having a thickness of 0.25 m and a width of 1.2 m. 10, the dipping nozzles 12 whose discharge ports 11 on both sides are oriented in the horizontal direction are arranged so that the position of the discharge ports 11 from the meniscus portion is 250 mm at the center of the continuous casting mold 10 and 100 mm below the position. The magnetic pole 13 having a width of about 50 mm, which is made of an electromagnet, is arranged to face each other, and a static magnetic field of about 0.3 T is generated in the mold to cast at a speed of 0.6 m / min.
Was cast in.

As a result, the temperature of the molten metal in the meniscus portion was increased and the flow velocity thereof was secured, so that powder flaws could be prevented and pinholes could be prevented, and stainless cast pieces with few surface defects during rolling could be manufactured. .

For a comparative experiment, a dipping nozzle having a molten metal discharge angle of 15 degrees was used, and the experiment was conducted under the same conditions as in the above-mentioned embodiment except that the molten metal temperature at the meniscus portion was the magnetic pole 13. Although it rose more than when it was not excited, many bubbles were generated in the center due to the counter flow of MHD, and many pinholes were generated. Further, the temperature deviation in the width direction in the continuous casting mold 10 became large, resulting in a slab with disturbed oscillation marks. When this slab was rolled, streak-like defects (heage) frequently occurred.

Next, the excitation of the magnetic poles 13 is weakened so that the magnetic flux density in the continuous casting mold 10 is 0.1T.
Although the pinholes decreased with the decrease of the D-opposed flow, the powder in the meniscus portion in the mold solidified to generate slag bear, and powder flaws occurred during rolling of the slab. This is because the discharge angle of the immersion nozzle is 15 degrees downward and the magnetic flux density forming the brake zone is also small, so that the molten metal also flows downward, and as a result, the molten metal speed and the molten metal temperature of the meniscus portion decrease. To be judged.

[0011]

As is apparent from the above description, the method for producing a cast slab having excellent surface properties according to claims 1 and 2 effectively damps the molten metal discharged from the dipping nozzle, resulting in extremely few defects. High cleanliness steel can be manufactured stably.

[Brief description of drawings]

FIG. 1 is a schematic explanatory diagram of a method for manufacturing a cast slab having excellent surface properties according to an embodiment of the present invention.

FIG. 2 is a graph showing the relationship between the powder entrainment index and the immersion nozzle upward angle.

FIG. 3 is a graph showing the relationship between the powder entrainment index, molten steel temperature deviation, and the distance from the meniscus portion to the magnetic pole upper end position.

FIG. 4 is an explanatory diagram of a casting situation when a static magnetic field is provided in a lower portion of the mold.

FIG. 5 is an explanatory view showing an abnormal growth state of a solidified shell.

[Explanation of symbols]

 10 Continuous casting mold 11 Discharge port 12 Immersion nozzle 13 Magnetic pole

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ryoichi Kutomi 1-1 Hibahata-cho, Tobata-ku, Kitakyushu-shi, Fukuoka New Nippon Steel Corporation Yawata Works

Claims (2)

[Claims] 1. A method of continuously producing molten slab by supplying molten metal from a dipping nozzle having discharge ports on both left and right sides to a mold having a rectangular cross section, wherein the casting is slightly lower than the dipping nozzle in the entire width direction. A method for producing a cast slab having excellent surface properties, characterized in that a static magnetic field having a substantially uniform magnetic flux density that spreads is generated, and the discharge port of the immersion nozzle is directed upward 15 degrees from the horizontal. 2. The method for producing a slab having excellent surface properties according to claim 1, wherein the static magnetic field has an upper end located 200 to 800 mm below the meniscus portion.