JPS63230258A - Method and apparatus for continuously casting steel by using static magnetic field - Google Patents

Abstract

PURPOSE:To surely prevent entrapping phenomenon of non-metallic inclusion and to stably and continuously cast a cast slab having good quality by pouring molten steel in center part of static magnetic field in a mold of continuous casting machine and immediately controlling flow of the molten steel by the static magnetic field, to reduce the flowing speed. CONSTITUTION:In the continuous casting apparatus, one pair of first static magnetic poles 3 are arranged almost at the center part of wide width side face of upper part of the mold 1 for the continuous casting machine. The center line linking the centers C of the magnetic poles almost coincides with the discharging hole 8 of a submerged nozzle 7 for pouring the molten steel. The max. magnetic flux density of the above static magnetic pole 3 is to be >=about 1000G and desirably >=1700G under condition of about 1-4 ton/min practically pouring speed of the molten steel. By this method, the molten steel 5 poured in the mold 1 is smoothly flowed immediately by reducing flow speed without development of turbulent flow at the high magnetic flux density part 9. Speed of this flow is further reduced at the equal density line 11 to become uniform dispersing molten steel flow 12. By this method, the entrapment of generated non-metallic inclusion is prevented by the high speed molten steel flow as showing by the broken line arrow, and held to the top part of the meniscus part in the mold 1.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method and apparatus for casting steel, particularly a continuous casting method and apparatus for obtaining clean steel with few oxide-based nonmetallic inclusions using a static magnetic field. It is something.

(Prior Art) Conventionally, during continuous casting of steel, it has been a problem that oxide-based nonmetallic inclusions contained in the injected molten steel are deeply engulfed inside the slab by the injected molten steel flow. In a curved continuous casting machine, non-metallic inclusions that have been deeply rolled up do not float up to the meniscus area and are caught on the lower surface of the solidified shell, causing defects such as slivers and blisters on the surface of the rolled steel sheet. The problem is that the problem occurs.

As a method to solve the above-mentioned problem,
Publication No. 356 describes that at least one static magnetic field is provided in the mold, and by causing the injected molten steel to flow through the static magnetic field, the speed of the injected molten steel flow is reduced and the flow direction is controlled. .

(Problems to be Solved by the Invention) However, as disclosed in the above publication, when the injected molten steel is caused to flow in the direction of the static magnetic field from outside the static magnetic field, the injected molten steel has a uniform magnetic flux distribution of the static magnetic field. Since the molten steel tends to flow along the density line, it is necessary to control the flow direction of the molten steel in a direction that slows down the velocity of the molten steel. If the control is not carried out completely, there is a problem that oxide-based nonmetallic inclusions will be deeply involved in the slab, making it difficult to stably obtain high quality slabs. There is.

The main purpose of the present invention is to discharge molten steel from a submerged nozzle into the center of a static magnetic field, so that the flow of the injected molten steel is immediately controlled and decelerated by the static magnetic field, thereby ensuring the entrainment of non-metallic inclusions. The purpose of the present invention is to provide a continuous casting method that can prevent such problems.

Another object of the present invention is to discharge molten steel from a submerged nozzle into the center of a first static magnetic field, to immediately decelerate the molten steel by the first static magnetic field, and to direct the decelerated downward flow from the first static magnetic field to the second static magnetic field. Provided is a continuous casting method that can reliably prevent entrainment of nonmetallic inclusions even if the initial velocity or injection velocity of molten steel discharged from a submerged nozzle into a first static magnetic field is high. This is what I am trying to do.

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

(Means for Solving the Problems) According to the present invention, as shown in FIG.
In a continuous steel casting method in which the flow of molten steel injected into the first static magnetic field is controlled by a static magnetic field, the molten steel is injected into the center of the first static magnetic field 4 to reduce the flow velocity of the injected molten steel 5.
It is characterized by causing 2.

Further, according to the present invention, as shown in FIG.
The flow rate of the injected molten steel 5 is decelerated by injecting it into the center of the static magnetic field 4, and the direction of the decelerated downward flow A1 of the molten steel from the first static magnetic field 4 is controlled in a predetermined direction by at least one second static magnetic field 14. The method is characterized in that the speed of the decelerated downward flow A of molten steel is further reduced to produce a dispersed molten steel flow 16.

According to the present invention, as a continuous casting apparatus for carrying out the above-mentioned method, as shown in FIG. A pair of first static magnetic poles 3 are installed, and a center line 6 (see FIG. 2) connecting the magnetic pole centers C of the first static magnetic pole set 3 is made to almost coincide with the discharge hole 8 of the immersion nozzle 7 for injecting molten steel. It is characterized by

Further, as another feature of the apparatus according to the present invention, as shown in FIG. 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 molten steel injection immersion nozzle 7, and the first
At a position below the static magnetic pole 3, for example, at least one
It is characterized by providing a pair of second magnetostatic poles 13.

In carrying out the present invention, it is preferable to install the first magnetostatic pole 3 at the upper center of the wide side surface of the mold, and to install the second magnetostatic pole 13 at both ends of the lower part.

Further, in carrying out the present invention, when the practical injection rate of molten steel is 1 to 4 tons min, the maximum magnetic flux density of the first static magnetic field 4 is set to 1000 Gauss or more, particularly preferably 17
It is preferable to set it to 00 Gauss or more. In particular, by 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 reduced to 2.
It is preferable that the magnetic flux density of the second static magnetic field 14 be 500 Gauss or more, and the magnetic flux density of the second static magnetic field 14 be 1000 Gauss or more. Further, the initial velocity of the injected molten steel is preferably 1 m/sec or less, preferably 0.5 m/sec or less.

(Function) As shown by 5 in FIG. 1, the molten steel injected into the mold 1 near the center line 6 connecting the discharge hole 8 of the submerged nozzle 7 and the center C of the first static magnetic pole 3.3 is Under the action of the high magnetic flux density portion 9 of the magnetic field 4, the flow is directly decelerated and flows smoothly, with almost no turbulence.

When this smooth flow proceeds across the isopycnal line 11, a force acts to block this flow, causing a tendency to flow along the isopycnal line 11, and as a result, the flow is decelerated.
As shown in the dispersed molten steel flow 12, the molten steel is uniformly dispersed.

As a result, the high-speed injection molten steel flow shown by the broken line arrow in Fig. 1 does not occur, and the entrainment phenomenon of non-metallic inclusions that conventionally occurred due to such high-speed injection molten steel flow is eliminated, and the non-metallic inclusions are removed. 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. Practical injection rate below 1000 Gauss1
-4 t/min, sufficient flow dispersion effect cannot be expected.

Since it is an interaction between the magnetic field and the flow, the effect is small if the flow is too fast. This is because it passes through the range of the magnetic field in a short time. Therefore, from the effect of impulse, 100
When it is 0 Gauss, the initial velocity is lower than 0.5 m/s, and 1
When the velocity is 700 Gauss, the initial velocity is 1. It is preferable to make it lower than Om/s.

As mentioned above, when molten steel is discharged from the discharge port 8 of the submerged nozzle 7 into the center of the first static magnetic field 4 between the first static magnetic poles 3.3, the strength of the first static magnetic field 4 is If the initial velocity or 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 descends at a high speed as shown by the dashed arrow. No flow occurs.

However, if the initial velocity or injection velocity of the discharge flow 5 is the first static magnetic field 4
If the strength is not sufficiently low compared to the strength of , the discharge flow is not decelerated sufficiently, and a decelerated downward flow AI (see FIG. 3) is generated that descends from the first static magnetic field 4 along the short sides of the mold.

Therefore, according to the present invention, when performing continuous casting at a high molten steel injection rate, for example, as shown in FIG. The second static magnetic field 14 is installed at both ends of the wide side of the mold, that is, at positions adjacent to the short sides of the mold. This second static magnetic field 14 acts as a non-contact weir on the decelerated descending person. Therefore, the decelerated downdraft person 1 is decelerated and dispersed by the second static magnetic field [4, as shown by arrows 16, without deeply entering the second static magnetic field 14. In this way, even if the initial velocity or 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 nonmetallic inclusions from being brought deep into the slab.

When using the first static magnetic field 4 and the second static magnetic field 14 according to the present invention, the strength of the first static magnetic field 4 is set to 2500 Gauss, and the strength of the second static magnetic field 4 is
By setting the strength of the static magnetic field 14 to 100 Gauss or more, it is possible to prevent nonmetallic inclusions from entering at a practical injection rate of 1 to 4 Lon/min.

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

(Example) Example (1) In a curved slab continuous casting machine that continuously casts slabs with a thickness of 220 mm and a width of 1350 to 1500 mm,
A magnetic pole with a width of 500 mm and a width of 500 mm was placed on the wide side of the mold so that the center of the magnetic pole almost coincided with the center of the discharge hole of the immersion nozzle, and the strength of the magnetic field at the center of the magnetic field was set to 1700 Gauss.

Molten steel was injected at an injection rate of 3.2 t/min using a submerged nozzle with a total discharge hole cross-sectional area of 150 cm2 (initial velocity of molten steel alone was 50 cm/sec). Layer killed steel for cold rolling 5
A total of 14oot was cast, but most of the cold-rolled products were slivers and blisters! ! 1 (maintained good surface quality.

Example (2) An experiment was conducted under the same conditions as Example (1) except that the flow rate at the discharge hole was 70 cm/sec. Slight blistering occurred in the cold rolled product.

Example (3) An experiment was conducted with the magnetic field strength at the center of the magnetic field set to 1000 Gauss, and other conditions being the same as in Example (1). Slight blisters and slivers were generated in the product after cold rolling.

Example (4) In a curved slab continuous casting machine that continuously casts slabs with a thickness of 220 mm and a width of 1350 to 1500 mm, vertical, l:jl
! , a 325 mm magnetic pole was installed on the wide side of the mold with the center of the magnetic pole almost matching the center of the discharge hole of the immersion nozzle, and a magnetic pole of 160 mm long and 4325 mm was placed on the end of the wide side with the bottom surface at the bottom of the mold. Installed to match; The strength of the first quiet magnetic field at the center of the wide surface is 2500 Gauss,
The strength of the second static magnetic field was set to 1000 Gauss. Molten steel was injected at an injection rate of 3.5 L/+nin using a submerged nozzle with a total discharge hole cross-sectional area of 150 cm2.

A total of 1,400 tons of 5 heats of 1-killed steel were cast for cold rolling, and the cold-rolled products maintained good surface quality with almost no sleepers or blisters until the end.

Example (5) An experiment was conducted under the same conditions as Example (4) except that the injection rate was 4.5 t/min. Slight blistering occurred in the cold rolled product.

Example (6) The strength of the first static magnetic field at the center was set to 2500 Gauss, and the strength of the second static magnetic field at the ends was set to 500 Gauss, so there were only a few blisters and sleepers in the product after cold rolling. It occurred in

(Effects of the invention) In order to confirm the effects of the invention, comparative examples (1) and (2)
Examples (1) and (2) of the present invention were obtained by experimenting with the conventional example and the conventional example.
, (3).

Table 1 shows a comparison with (4), (5), and CG).

Comparative Example (1) Among the conditions in Example (1) of the present invention described above, the strength of the magnetic field was 800 Gauss or less, and the initial velocity was 75 cm / s.
I changed it to ec. As a result, the steel IJ in cold rolled products
- The occurrence of bars increased slightly and blisters occurred frequently.

Comparative Example (2) The strength of the first static magnetic field at the center is 1000 Gauss, the strength of the second static magnetic field at the end is 500 Gauss, the injection rate is 4, and Qt.
/min. As a result, the occurrence of sleepers in cold-rolled products increased slightly, and blisters occurred frequently.

Conventional Example As a conventional example, molten steel was injected using two static magnetic fields according to the conventional method described in JP-A-57-17356 f-. As a result, the cold-rolled product had slightly more blisters and sleepers.

According to the present invention, stable casting is possible even if the discharge position of the molten steel from the immersion nozzle changes slightly, and the flow of molten steel discharged from the immersion nozzle is quickly decelerated and averaged, eliminating strong local flows. As a result, non-metallic inclusions and air bubbles are not brought deep into the mold, and the amount of non-metallic inclusions and air bubbles trapped inside the continuously cast slab is significantly reduced, resulting in improved quality. 1) The advantage is that steel materials can be used sparingly.

[Brief explanation 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 of the mold section along the line It is a diagrammatic longitudinal sectional view of a mold part showing an embodiment of the invention (It). 1... Mold 2... Mold wide side surface 3...
- First static magnetic pole 4... First static magnetic field 5... Injected molten steel 6... Center line 7... Immersed nozzle Bottom... Lower end discharge hole 9... High magnetic flux store portion 10... Low magnetic flux density part

Claims (1)

[Claims] 1. In a continuous steel casting method 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
A continuous casting method for steel using a static magnetic field, characterized by injecting the molten steel into the center of the static magnetic field to slow down the flow velocity of the molten steel. 2. In a continuous steel casting method 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
the molten steel is injected into the center of the static magnetic field to decelerate the flow velocity of the molten steel, and the decelerated downward flow of the molten steel from the first static magnetic field is controlled by at least one second static magnetic field installed below the first static magnetic field. A continuous casting method for steel using a static magnetic field characterized by deceleration. 3. A pair of first static magnetic poles were arranged at the top of the wide side of the mold of the continuous casting machine, and the center line connecting the magnetic pole centers of the first static magnetic poles was made to almost match the discharge hole of the immersion nozzle for injecting molten steel. A continuous steel casting device using a static magnetic field, characterized by: 4. A pair of first static magnetic poles are arranged at the upper part of the wide side of the mold of the continuous casting machine, and the center line connecting the magnetic pole centers of the first static magnetic poles is made to almost coincide with the discharge hole of the immersion nozzle for pouring molten steel, Said first
1. A continuous casting apparatus for steel using a static magnetic field, characterized in that at least one pair of second static magnetic poles is installed below the wide side surface of the mold at a position below the static magnetic poles.