JPH04344858A - Method for continuously casting steel utilizing static magnetic field - Google Patents

Abstract

PURPOSE:To obtain a cast slab excellent in quality without any product defect by controlling molten steel flowing speed in the transverse direction of a mold so as to always be uniform even in the case casting condition is changed. CONSTITUTION:At the time of executing the continuous casting while impressing the static magnetic field to a whole zone in the transverse direction of a mold 1 in order to control discharged spouting flow of a molten steel 5 supplied into the mold 1 for continuous casting from an immersion nozzle 2, magnetic flux density distribution in the transverse direction of the mold 1 allows to correspond with the flowing speed of the molten steel in the mold 1 and the magnetic flux density in the vicinity of the short side part of the mold is made larger than that at transverse central part and particularly, the molten steel is cast while impressing the magnetic field so as to become 1.2-3.0 of the strength ratio at both sides. By this method, the molten steel flowing speed in the transverse direction of the mold 1 is always made to uniform, and the cast slab excellent in quality without any defect can be stably manufactured.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is a method for continuous casting of steel using a static magnetic field, in particular, it is possible to obtain a uniform flow of molten steel in the width direction of the mold without considering casting conditions, and it is possible to avoid product defects. This paper proposes a method of casting while controlling the effect of a static magnetic field to prevent frequent occurrence of slivers, UT defects, blisters, and blisters.

0002

BACKGROUND OF THE INVENTION In continuous steel casting, controlling the flow of molten steel within a mold is extremely important in reducing internal defects and surface defects in the cast slab.

Conventionally, means for controlling the flow of molten steel in the mold have been disclosed in Japanese Patent Publication No. 2-20349 and Japanese Patent Application Laid-Open No.
As disclosed in Japanese Patent No. 284750, by applying a static magnetic field to the molten steel in the mold and dispersing or decelerating the strong flow in the mold by the effect of a so-called electromagnetic brake, the molten steel flow can be controlled, that is, the mold width A method has been proposed to equalize the directional flow of molten steel.

[0004] In particular, Japanese Patent Application Laid-Open No. 2-284750,
This is an improvement on the problem faced by the technique disclosed in Japanese Patent Publication No. 2-20349, that is, the flow of molten steel in the mold due to non-uniformity of the magnetic field. That is, this Japanese Patent Application Laid-Open No. 2-284
The disclosure of Japanese Patent No. 750 is that if a magnetic field is applied only to a part of the width of the mold, the molten steel flow will concentrate in the areas where the magnetic field is weak, resulting in an unexpected flow pattern. Therefore, in order to completely control the flow of molten steel, it is necessary to apply a magnetic field across the entire width of the mold. For this purpose, by applying a static magnetic field parallel to the thickness direction of the slab over the entire width of the mold, the surface flow velocity of the molten steel is suppressed and the strong downward flow of the mold is decelerated, resulting in high quality casting. Suggestions are made on how to cast pieces.

[0005]

[Problems to be Solved by the Invention] However, even with the conventional continuous casting method improved in this way, the present inventors investigated the flow pattern of molten steel in the mold through a model experiment using mercury. However, it was found that the desired flow control effect was not necessarily obtained. Moreover, even when applied to an actual continuous casting machine, although the surface and internal quality of the slab has been improved to some extent, it has not yet reached the point where satisfactory results are obtained under all casting conditions. The reality is that there is not.

Therefore, the present invention aims to advantageously solve the above-mentioned problems of the prior art.In particular, even if the casting conditions such as the molten steel supply rate change, the molten steel flow velocity in the mold width direction is always maintained. The objective is to establish a continuous casting technology that utilizes a static magnetic field that is effective in obtaining excellent quality slabs without product defects by controlling the casting to be uniform.

[0007]

[Means for Solving the Problems] As a result of intensive research to achieve the above-mentioned object, the present inventors have developed a method for producing molten steel that has a uniform flow velocity distribution in the width direction of the mold in continuous casting of steel using a static magnetic field. It was discovered that in order to obtain a flow, it is necessary to apply a static magnetic field to the entire width direction of the mold so that the magnetic flux density distribution corresponds to the flow velocity distribution of molten steel in the mold, and the present invention was conceived.

That is, the present invention provides continuous casting while applying a static magnetic field to the entire width direction of the mold in order to control the discharge jet of molten steel supplied from the immersion nozzle into the continuous casting mold. , using a static magnetic field characterized in that casting is performed while applying a magnetic field so that the magnetic flux density distribution of the magnetic field applied to the entire width direction of the mold corresponds to the flow velocity distribution of the molten steel in the mold. A continuous casting method for steel, wherein the present invention preferably makes the magnetic flux density of the magnetic field applied near the short side of the mold larger than the center of the width of the mold; Adjust the ratio of the magnetic flux density of the magnetic field applied near the sides and the center of the mold width to be within the range of 1.2 to 3.0, assuming that the magnetic flux density of the center of the mold width is 1. is preferred.

[0009]

[Operation] The continuous casting method of the present invention achieves uniform braking of the molten steel flow in the mold, which is essential for producing defect-free slabs, even when continuously casting low C-Al killed steel at high speed. It is something to do.

By the way, the present inventors have investigated in detail the flow pattern and electromagnetic force distribution within the mold through mercury model experiments and numerical simulations in which the mercury flow velocity is measured using a magnetic sensor.

First, in an example in which no static magnetic field is applied to the molten steel in the mold, the jet flow from the immersion nozzle collides with the short side of the mold, as shown in FIG. One part turns upward and becomes a molten steel surface flow, and the other part turns into a strong flow descending along the short side. These molten steel flows can cause slag to be entrained on the surface of the molten steel pool, or deoxidized products and air bubbles can be carried deep into the molten steel pool, ultimately resulting in surface defects or internal defects in product steel sheets. understood.

Next, in the prior art, as shown in FIG. 4(b) and FIG.
As shown in (c), although the above-mentioned upward reverse flow and strong downward flow of the molten steel flow are weakened, the damping is insufficient. That is, in the example shown in FIG. 4(b), since the magnetic field is not applied to the entire width of the mold, a strong flow occurs in the portion where the magnetic field is relatively weak, and the molten steel flow cannot be sufficiently damped. On the other hand, in the example shown in Fig. 4(c) in which a magnetic field is applied to the entire width of the mold, the molten steel flow ejected from the immersion nozzle once collides with the short side of the mold, and then the direction of the molten steel flow is divided into vertical and horizontal directions. Therefore, the flow near the short side of the mold becomes very complicated. This means that near the center of the mold in the width direction, there is little turbulence in the molten steel flow, and the effect of electromagnetic braking is sufficiently exerted even with the application of a relatively small magnetic field, whereas near the short sides of the mold, as mentioned above, It was found that the effect of electromagnetic braking becomes weaker as the molten steel flow becomes more complex.

Therefore, in the present invention, when a static magnetic field is applied to the entire width direction of a continuous casting mold in order to control the flow of molten steel in the mold, the magnetic field applied to the entire width direction of the mold is It was decided to provide a magnetic field distribution such that the magnetic flux density distribution corresponds to the flow velocity distribution of molten steel in the mold, that is, the magnetic field is strong near the short sides of the mold. In this case, the ratio of the magnetic flux density of the magnetic field applied near the short side of the mold to the center of the mold width is within the range of 1.2 to 3.0, where the magnetic flux density of the center of the mold width is 1. It is preferable that

The reason for performing such magnetic flux density distribution adjustment is to variously change the magnetic flux density near the short sides of the mold, assuming that the magnetic flux density at the center of the mold width is 1, so that the downward flow velocity at the center of the mold width can be adjusted. This is based on the results of investigating the magnitude of the downward flow velocity near the short side of the mold when the value is 1. That is, as shown in Figure 8, when a static magnetic field is applied only near the short side of the mold (point A in the figure), or when the ratio of the magnetic flux density near the short side and the center exceeds 3.0. (range B in the figure), the flow tends to concentrate in the center of the width, and the desired effect cannot be obtained. Also, if the ratio of magnetic flux densities is less than 1.2, the downward flow is not sufficiently damped. This is because it is not possible to prevent inclusions from being drawn into the slab.

As described above, according to the continuous casting method of the present invention, as shown in FIG. 5(a), the strong downward flow along the short side of the mold is weakened, and a substantially uniform downward flow is obtained in the width direction of the mold. be able to. Figure 5 shows a mercury model experiment in which the mercury flow velocity is measured using a magnetic sensor, and a conventional method that provides a uniform magnetic field distribution in the width direction of the mold is used (Figure 5 (b)).
), and in the case of the method of the present invention in which a magnetic field is applied so that the magnetic flux density near the short side of the mold becomes large (Fig. 5 (
a)). Here, the arrows in the figure indicate the magnitude and direction of the mercury flow velocity measured by the sensor.

[0016]

【Example】

(Example 1) An electromagnet for applying a magnetic field was made with a thickness of 260 mm,
Figures 1 (a) and (b) are placed in a continuous casting mold with a width of 1200 mm.
The low carbon steel was cast at a molten steel supply rate of 4.0 t/min while applying a static magnetic field parallel to the thickness direction of the slab, facing the molten steel surface in the mold and the lower area of the mold. .

In carrying out the embodiment of the present invention, FIG.
Using an electromagnet iron core with the shape shown in (a),
A magnetic field was applied so that the magnetic flux density distribution in the mold width direction was as shown in (a) (The magnetic flux density applied during casting was 1200 Gauss at the center of the width and 1800 Gauss near the short sides.) . On the other hand, in implementing the comparative example, an electromagnet iron core with a shape as shown in Fig. 2(b) was used, and a magnetic flux density was uniform across the entire mold width direction (range of 1200 mm) as shown in Fig. 3(b). A magnetic field was applied so as to have a distribution (the magnetic flux density applied during casting was 1200 Gauss over the entire width direction).

In this way, for the slabs cast in the above examples and comparative examples, the number of slags on the slab surface and the total oxygen analysis value in the slab (1/4 thickness part)
The results of the comparison are shown in FIGS. 6 and 7, respectively. As is clear from these figures, according to the method of the present invention,
It can be seen that the quality of the slab surface and interior can be significantly improved.

(Example 2) Using the same mold and casting conditions as in Example 1, the ratio of the magnetic flux density near the short side of the mold and the center of the width was changed by changing the shape of the iron core of the electromagnet for applying a magnetic field. Cast. FIG. 9 shows the results of comparing the amounts of inclusions in the slabs thus obtained. As is clear from this figure, the ratio of magnetic flux density near the short side of the mold to the center of the width is set to 1.
．． By setting it in the range of 2 to 3.0, the amount of inclusions in the slab can be significantly reduced.

[0020]

[Effects of the Invention] As explained above, according to the present invention,
The magnitude of the magnetic flux density in the width direction of the mold is made different, and the vicinity of the short side of the mold is made larger than the center of the width, and in particular, the strength ratio is set to 1.
By setting it in the range of 2 to 3.0, it is possible to dampen the strong downward flow along the short side of the mold and obtain a uniform flow of molten steel in the width direction of the mold, which in turn significantly improves the quality of slabs and final products. can be improved.

[Brief explanation of the drawing]

FIG. 1 is a front view (a) and a side view (b) showing the arrangement of electromagnets in a mold in the implementation of the method of the present invention.

[Figure 2] (a) Iron core for magnet according to the method of the present invention, (b)
It is a figure showing the structure of the iron core for magnets concerning the conventional method.

FIG. 3 is a diagram showing the magnetic flux density distribution in the mold width direction when the magnet iron core shown in FIGS. 2(a) and 2(b) is used.

[Fig. 4] Molten steel in the following cases: (a) when a magnetic field is applied to the entire width of the mold by the method of the present invention, (b) when a magnetic field is applied to the mold by the conventional method, (c) when no magnetic field is applied to the mold. It is a figure showing a flow pattern.

FIG. 5 is a diagram showing flow velocity measurement results from mercury model experiments (a) for the method of the present invention and (b) for the conventional method.

FIG. 6 is a diagram comparing the number of grooves on the slab surface obtained by the method of the present invention and the conventional method.

FIG. 7 is a diagram comparing the total oxygen analysis values in the slab obtained by the method of the present invention and the conventional method.

FIG. 8 is a diagram showing the relationship between the magnetic flux density ratio of the short side and the center of the mold and the downward flow velocity of the short side in a mercury model experiment.

FIG. 9 is a diagram showing the relationship between the magnetic flux density ratio of the short side part of the mold and the center part and the amount of inclusions in the slab.

[Explanation of symbols]

1 Continuous casting mold 2 Immersion nozzle 2a Discharge port 3 Iron core for electromagnet 4 Slab 5 Molten steel 6 Coil for magnetic field generation

Claims (3)

[Claims] 1. In order to control the discharge jet of molten steel supplied into the continuous casting mold from the immersion nozzle, when performing continuous casting while applying a static magnetic field to the entire width direction of the mold, Continuous casting of steel using a static magnetic field characterized by casting while applying a magnetic field so that the magnetic flux density distribution of the magnetic field applied throughout the width direction corresponds to the flow velocity distribution of molten steel in the mold. Method. 2. The method according to claim 1, wherein the magnetic flux density of the magnetic field applied near the short side of the mold is made larger than that at the center of the width of the mold. 3. The ratio of the magnetic flux density of the magnetic field applied near the short side of the mold to the center of the width of the mold is 1.2 to 3.0, assuming that the magnetic flux density of the center of the width of the mold is 1. A method according to claim 1, characterized in that the method is within the range of.