JPH0790339B2 - Method and apparatus for continuous casting of steel using static magnetic field - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method and an apparatus for producing steel, and more particularly to a continuous casting method and apparatus for obtaining a clean steel containing a small amount of oxide-based non-metallic inclusions by using a static magnetic field. It is a thing.

(Prior Art) Conventionally, during continuous casting of steel, it has been a problem that oxide-based non-metallic inclusions contained in the molten steel to be cast are deeply wound inside the slab by the molten steel flow to be cast. In a curved continuous casting machine, non-metallic inclusions that are once deeply caught do not float up to the meniscus portion, but are caught on the lower surface of the solidified shell, and defects such as slivers and blisters appear on the surface of the rolled steel sheet. There is a problem that occurs.

As a method for solving the above-mentioned problem, Japanese Patent Laid-Open No. 17356/1982
The publication describes that at least one static magnetic field is disposed in a mold, and the molten steel flow is injected into the static magnetic field to reduce the velocity of the molten steel flow and to control the flow direction.

(Problems to be Solved by the Invention) However, as disclosed in the above publication, when the injected molten steel is flowed from the outside of the static magnetic field to the static magnetic field, the injected molten steel has an equal density of the velocity distribution of the static magnetic field. Since it tends to flow along the line, it is difficult to control the flow direction of the molten steel in the direction of slowing down the velocity of the molten steel flow, it is necessary to perform extremely delicate control, and the control is completely performed. If not present, there is a problem that the oxide-based non-metallic inclusions are deeply involved in the slab, and there is a problem that it is difficult to stably obtain a good quality slab.

The main object of the present invention is to immediately control the flow of molten steel injected by discharging molten steel from the immersion nozzle to the center of the static magnetic field by means of the static magnetic field, thereby ensuring the inclusion phenomenon of non-metallic inclusions. It is intended to provide a continuous casting method capable of preventing the above problems.

Another object of the present invention is to discharge molten steel from the dipping nozzle to the center of the first static magnetic field and immediately decelerate it by the first static magnetic field, and reduce the decelerating downward flow from the first static magnetic field to the second static magnetic field. A continuous casting method capable of reliably preventing the entrainment phenomenon of non-metallic inclusions even if the initial speed or the injection speed of the molten steel discharged from the immersion nozzle into the first static magnetic field is high by this Is what you are trying to do.

Another object of the present invention is to provide a continuous casting apparatus for carrying out the above method.

(Means for Solving Problems) According to the present invention, as shown in FIG. 1, the mold 1 of the continuous casting machine is used.
In the continuous casting method of steel in which the flow of the molten steel injected into the inside is controlled by a static magnetic field, the molten steel is directly injected into the central portion of the first static magnetic field 4 to generate a dispersed molten steel flow 12 that reduces the flow velocity of the injected molten steel 5. It is characterized by tightening.

Further, according to the present invention, as shown in FIG.
The flow velocity of the injected molten steel 5 is reduced by directly injecting it into the center of the static magnetic field 4, and the direction of the decelerating downward flow A ₁ of the molten steel from the first static magnetic field 4 is changed to a predetermined direction by at least one second static magnetic field 14. It is characterized in that the velocity of the decelerating downward flow A ₁ of the molten steel is further reduced by controlling to generate the dispersed molten steel flow 16.

According to the present invention, as a continuous casting apparatus for carrying out the above-described method, as shown in FIG. 1, a set of a set of the upper portion of the mold 1 of the continuous casting machine, for example, at a substantially central position of the wide side surface 2 is provided. A pair of first static magnetic poles 3 is installed, and a center line 6 (see FIG. 2) connecting the magnetic pole centers C of the first static magnetic pole set 3 is substantially aligned with the discharge hole 8 of the molten steel pouring immersion nozzle 7. Is characterized by.

Further, as another feature of the apparatus according to the present invention, as shown in FIG. 3, a pair of first static magnetic poles 3 is provided at an upper portion of the mold 1 of the continuous casting machine, for example, at a substantially central position of the wide side surface 2. Is installed, the center line 6 connecting the magnetic pole centers C of the first static magnetic pole set 3 is almost aligned with the discharge hole 8 of the immersion nozzle 7 for injecting molten steel, and is located below the first static magnetic pole 3, for example, the wide side surface of the mold. At least 1 in contact with each of the short side surfaces 15 at both ends of the lower end of 2.
It is characterized in that a pair of second static magnetic poles 13 is provided.

In carrying out the present invention, it is preferable to install the first static magnetic pole 3 at the upper center of the wide side surface of the mold and the second static magnetic poles 13 at both lower end portions.

Further, in practicing the present invention, the maximum magnetic flux density of the first static magnetic field 4 is 1000 gausses or more, particularly preferably 1700 gausses or more when the practical injection speed of molten steel is 1 to 4 ton / min. good. In particular, using the first static magnetic field 4 and the second static magnetic field 14, the magnetic flux density of the first static magnetic field 4 is 2500 gauss, the second static magnetic field
It is preferable that the magnetic flux density of 14 is 1000 Gauss or more. The initial velocity of the molten steel injected is 1 m / sec or less, preferably 0.5 m / sec.
The following is good.

(Operation) As shown by 5 in FIG. 1, the molten steel injected into the mold 1 in the vicinity of the center line 6 connecting the centers C of the first static magnetic poles 3 from the discharge hole 8 of the immersion nozzle 7 is the first static Under the influence of the high magnetic flux density portion 9 of the magnetic field 4, turbulence is hardly generated, and the magnetic field 4 is immediately decelerated and smoothly flows. When this smooth flow tries to proceed across the isopycnic line 11, the force that blocks this flow works,
There is a tendency to flow along the isopycnic line 11, which results in the flow being slowed down and evenly distributed as shown by the dispersed molten steel flow 12.

As a result, the high-speed injected molten steel flow as shown by the broken line arrow in FIG. 1 is not generated, and the entrainment phenomenon of the non-metallic inclusions generated by such a high-speed injected molten steel flow is eliminated, and the non-metallic inclusions are It is held above the meniscus in the mold.

The strength of the magnetic field is preferably 1000 gauss or more, preferably about 1700 gauss, and the stronger the better.
If it is lower than 1000 gauss, sufficient flow dispersion action cannot be expected at a practical injection rate of 1 to 4 t / min.

The effect is small even when the flow is too fast because it is an interaction between the magnetic field and the flow. This is because the range of the magnetic field is passed in a short time. Therefore, from the effect of impulse, it is preferable that the initial velocity is lower than 0.5 m / s at 1000 gauss and the initial velocity is lower than 1.0 m / s at 1700 gauss.

As described above, when the molten steel is injected into the central portion of the first static magnetic field 4 between the first static magnetic poles 3 and 3 by being discharged from the discharge port 8 of the immersion nozzle 7, the strength of the first static magnetic field 4 is reduced. When the initial velocity or the injection speed of the molten steel discharge flow 5 discharged from the discharge hole 8 is sufficiently low, the molten steel discharge flow is immediately dispersed and decelerated by the first static magnetic field 4, and the high-speed descending as shown by the broken line arrow. No flow occurs.

However, the initial velocity or the injection velocity of the discharge flow 5 is the first static magnetic field 4
If the discharge flow is not sufficiently low, the deceleration flow is not sufficiently decelerated, and a deceleration down flow A ₁ (see FIG. 3) that descends from the first static magnetic field 4 along the short side surface of the mold is generated. .

Therefore, according to the present invention, for example, when continuous casting is performed at a high molten steel injection rate, as shown in FIG. 3, the continuous casting is performed at a position lower than the first static magnetic field 4 installed in the upper center of the mold 1. The second static magnetic field 14 is installed at both ends of the wide mold surface, that is, at positions adjacent to the short side surfaces of the mold. This second static magnetic field 14 acts as a non-contact weir for the decelerated downward flow A ₁ . Therefore, the decelerating downward flow A ₁ is decelerated and dispersed by the second static magnetic field 14 as indicated by an arrow 16 without entering deep inside the second static magnetic field 14. In this way
Even if the initial velocity or the injection velocity of the discharge flow is not sufficiently low with respect to the strength of the first static magnetic field 4, it is possible to prevent the non-metallic inclusions from being deeply brought into the slab.

When the first static magnetic field 4 and the second static magnetic field 14 are used according to the present invention, the strength of the first static magnetic field 4 is set to 2500 gauss and the second static magnetic field is set to 2500 gauss.
By setting the strength of 14 to 1000 Gauss or more, it is possible to prevent the entry of non-metallic inclusions at a practical injection rate of 1 to 4 ton / min.

Further, in order to prevent the entrainment of mold flux, it is preferable to arrange a small static magnetic pole near the meniscus.

(Example) Example (1) In a curved slab continuous casting machine for continuously casting a slab having a thickness of 220 mm and a width of 1350 to 1500 mm, a magnetic pole having a length of 325 mm and a width of 500 mm was used as a dipping nozzle with the magnetic pole center on the wide surface of the mold. The magnetic field strength at the center of the magnetic field is 17
I made it to 00 gauss. Molten steel was injected at an injection speed of 3.2 t / min with an immersion nozzle having a total discharge hole cross-sectional area of 150 cm ² (initial speed of molten steel 50 cm / sec). Cold-rolled Al killed steel 5 heat total
After casting 1400t, the cold rolled product maintained good surface quality with almost no sliver and blister until the end.

Example (2) An experiment was conducted under the same conditions as in Example (1) except that the flow rate at the discharge hole was set to 70 cm / sec. The cold-rolled product had slight blisters.

Example (3) An experiment was conducted by setting the strength of the magnetic field at the center of the magnetic field to 1000 gauss and the other conditions being the same as in Example (1). The product after cold rolling had slight blister and sliver.

Example (4) In a curved slab continuous casting machine that continuously casts a slab having a thickness of 220 mm and a width of 1350 to 1500 mm, a magnetic pole of 325 mm in length and width was used as a wide surface of the mold and the center of the magnetic pole was used as the center of the discharge hole of the immersion nozzle. The magnetic poles having a length of 160 mm and a width of 325 mm were set so as to substantially coincide with each other, and magnetic poles having a length of 160 mm and a width of 325 mm were installed at the ends of the wide surface so that the bottom surface was aligned with the bottom of the mold. The strength of the first static magnetic field at the center of the wide surface is 2500 gauss, the second
The strength of the static magnetic field was set to 1000 gauss. Molten steel was injected at an injection speed of 3.5 t / min with an immersion nozzle having a total discharge hole cross-sectional area of 150 cm ² .

A total of 1400 tons of 5 heats of Al-killed steel for cold rolling were cast, but the cold rolled product maintained good surface quality with almost no sliver or blister until the end.

Example (5) An experiment was conducted under the same conditions as in Example (4) except that the injection rate was 4.5 t / min. The cold-rolled product had slight blisters.

Example (6) The strength of the first static magnetic field in the central portion was 2500 gauss and the strength of the second static magnetic field in the end portion was 500 gauss. The cold-rolled product had little blister and sliver. It happened to.

(Effect of the invention) In order to confirm the effect of the present invention, the comparative examples (1) and (2) and the conventional example were tested, and the examples (1), (2) of the present invention,
The results are shown in Table 1 in comparison with (3), (4), (5) and (6).

Comparative Example (1) Under the conditions in the above-mentioned Example (1) of the present invention, the magnetic field strength was set to 800 gauss or less and the initial velocity was set to 75 cm / sec. As a result, the occurrence of three bars in the cold-rolled product was slightly increased and blisters frequently occurred.

Comparative Example (2) The strength of the first static magnetic field at the central portion was 1000 gauss, the strength of the second static magnetic field at the end portion was 500 gauss, and the injection rate was 4.0 t / min. As a result, the occurrence of three bars in the cold-rolled product was slightly increased and blisters frequently occurred.

Conventional Example As a conventional example, molten steel was injected using two static magnetic fields by the conventional method described in JP-A-57-17356. As a result, the cold-rolled product contained a little more blisters and three bars.

According to the present invention, stable casting can be performed even if the molten steel discharge position from the immersion nozzle fluctuates a little, the molten steel discharge flow from the immersion nozzle is immediately decelerated and averaged, and there is no strong local flow. As a result, non-metallic inclusions and air bubbles are not brought deep into the mold, and the amount of non-metal inclusions and air bubbles entrained in the slab continuous cast slab is significantly reduced to obtain a steel material of excellent quality. The effect that it can be obtained is obtained.

[Brief description of drawings]

FIG. 1 is a diagrammatic longitudinal sectional view of a mold part showing an embodiment according to the present invention, FIG. 2 is a diagrammatic sectional view showing a part as a section along the line II-II in FIG. 1, and FIG. It is a schematic longitudinal cross-sectional view of a mold part showing another embodiment of the invention. 1 ... Mold, 2 ... Wide side surface of mold 3 ... First static magnetic pole, 4 ... First static magnetic field 5 ... Injection molten steel, 6 ... Center line 7 ... Immersion nozzle, 8 ... Bottom discharge hole 9 …… High magnetic flux density part 10 …… Low magnetic flux density part 11 …… Constant density lines, 12 …… Dispersed molten steel flow 13 …… Second static magnetic pole, 14 …… Second static magnetic field 15 …… Dispersed molten steel flow, 16… … Short side of mold

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kenji Saito 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Technical Research Division (72) Inventor Satoshi Nakato 1 Kawasaki-cho, Chiba-shi Kawasaki Steel Co., Ltd. (72) Inventor Kenichi Sorimachi, 1-chome, Mizushima Kawasaki-dori, Kurashiki-shi, Okayama Prefecture (no address) Inside the Mizushima Steel Works, Kawasaki Steel Co., Ltd. Stock Company Technical Research Division (72) Inventor Katsuo Kinoshita 2-3-2 Uchisaiwaicho, Chiyoda-ku, Tokyo Kawasaki Steel Co., Ltd. Tokyo Head Office (56) Reference JP-A-61-199557 (JP, A) Sho 59-85653 (JP, U)

Claims (4)

[Claims] 1. A continuous casting method of steel in which the flow of molten steel injected into a mold of a continuous casting machine is controlled by a static magnetic field, the molten steel is directly injected into the center of the first static magnetic field to reduce the flow velocity of the molten steel. A method for continuously casting steel using a static magnetic field, which comprises: 2. In a continuous casting method for steel in which the flow of molten steel injected into the mold of a continuous casting machine is controlled by a static magnetic field, the molten steel is directly injected into the center of the first static magnetic field to reduce the flow velocity of the molten steel. The decelerating downward flow of molten steel from the first static magnetic field to the first
A continuous casting method for steel using a static magnetic field, characterized in that the steel is controlled and decelerated by at least one second static magnetic field installed below the static magnetic field. 3. A pair of first parts on the upper side of the wide side surface of the mold of the continuous casting machine.
A continuous casting machine for steel using a static magnetic field, wherein a static magnetic pole is provided, and a center line connecting the magnetic pole centers of the first static magnetic pole is made substantially coincident with a discharge hole of a molten steel injecting immersion nozzle. 4. A pair of first parts on the upper side of the wide side surface of the mold of the continuous casting machine.
A static magnetic pole is provided, and a center line connecting the magnetic pole centers of the first static magnetic pole is substantially aligned with the discharge hole of the immersion nozzle for injecting molten steel,
At least one pair of second static magnetic poles is disposed below the first static magnetic pole below the wide side surface of the mold, and is used for continuous casting of steel using a static magnetic field.