JPS5938065B2 - Electromagnetic stirring method for slabs in continuous casting - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electromagnetic stirring method for improving the casting structure of a slab that is continuously cast by continuous casting equipment with a low height and curved from a mold with a single radius of curvature.

In general, continuous casting equipment that curves from the mold with a single radius of curvature has many advantages, such as low equipment costs due to the low equipment height, and the ability to increase the length of the secondary cooling zone and increase casting speed. Because of this, it has been widely adopted in recent years.

This curved continuous casting equipment, for example, has a short side of 130 to 3
When continuously casting a large slab with a length of 00 mvt and a length of 900 to 2,600,771 on the long side, the wide side surface of the long side is drawn out while drawing a curved surface of a single arc.

This wide curved surface is generally supported by rolls, but this is to suppress the solidified shell from expanding due to the static pressure of the molten steel in the final solidified part of the slab, and to prevent the slab from expanding. It functions as a guide device that allows smooth movement along curved surfaces.

When a wide slab is continuously cast in this manner, the slab expands in the portion not in contact with the rolls, and is compressed in the portions in contact with the rolls.

When expansion and compression are repeated in this way, carbon, sulfur, phosphorus, etc. are largely segregated in the center of the slab, which significantly reduces the commercial value of the finished product and also adversely affects the mechanical properties.

It is already known that this center segregation can be reduced by producing a large number of equiaxed crystals in the center of the slab. A method has been proposed in which the solidified portion is electromagnetically stirred.

However, in continuous casting machines for large slabs, especially in continuous casting machines that support and guide slabs from the mold to 1/4 of the circumference with a single radius of curvature, in order to perform electromagnetic stirring using electromagnets, the rolls must be removed and the electromagnets installed. Therefore, a supporting and guiding device is required to replace the roll, which increases the equipment cost, and it is also extremely difficult to incorporate the electromagnet while maintaining the curved surface.

In order to eliminate such drawbacks in the electromagnetic stirring of a curved continuous casting machine, this invention provides a method for stirring partially solidified molten metal, which is characterized by applying a static magnetic field to the unsolidified molten portion of a slab using a permanent magnet. This is what we propose.

Next, an embodiment of the present invention will be described with reference to the drawings.

Figure 1 shows the main parts of a curved continuous casting machine for continuous casting of slabs, where 1 is the mold, 2 is the slab, and 3 is the secondary cooling zone with a single curved radius up to 1/4 circumference. A group of rollers forming a roller apron that supports and guides the slab.

Permanent magnets 4, 4' are provided between the rollers 3□, 3□ at arbitrary locations in the roller group.

This permanent magnet is arranged so that one magnetic pole face faces the slab surface and is placed close to it, and the magnetic poles of permanent magnets 4 and 4', which face both sides with the slab 2 in between, are opposite to each other. It will be done.

Further, each permanent magnet may be connected with a yoke so as to form a magnetic circuit so that the N and S poles of the plurality of permanent magnets alternately face the surface of the slab so as to span the entire length in the width direction of the slab. .

The permanent magnet has a residual magnetic flux density Br of 5 to 10 KG, a coercive force Hc of 5 to 10 KOe, and a maximum energy product (BrHc
) max is suitable, YCo5CeCo
5tPrCo5. A rare earth cobalt magnet having components such as SmCo5tSmCo5tS is optimal.

Then, rollers 3 and 3□ are each equipped with energizing brushes 5.
.

In order to prevent current from leaking from other rollers in this DC circuit, each roller is insulated from the continuous casting machine body at the bearing portion.

If continuous casting is performed using this device, 2
As shown in Fig. 2, a stationary magnetic field 6 whose main direction is perpendicular to the drawing direction is applied to the slab 2, which is in the middle of solidification in the next cooling zone, by opposed permanent magnets 4 and 4'. The case where two permanent magnets are fixed to the yoke on each side is shown).

On the other hand, by energizing the DC circuit, a DC current 7 flows inside the slab in the same direction as the direction in which the slab is pulled out.

Then, due to the interaction with the static magnetic field 5, an electromagnetic force F in the width direction of the slab acts on the unsolidified molten metal of the slab 2, the unsolidified molten metal is stirred, and the segregation at the center of the slab is eliminated.

In the above, permanent magnets 4, 4 are placed at one location on each side of the slab.
′ was explained, but as shown in FIG. 3, a plurality of permanent magnets 41, 4
' ? 42' t 43' 544/ are arranged oppositely, and the upper roller 3□ faces the uppermost permanent magnets 4□, 4□'.
.

3,' and the lower rollers 3□, 32' facing the lowermost permanent magnet 44t44' are respectively provided with energizing brushes 5,
5, each brush is connected to a DC power supply circuit, and electromagnetic force F is applied in the width direction of the slab at multiple locations above and below the solidified molten metal of the slab to simultaneously stir the metal at multiple locations.

In addition, in this invention, the stirring position in the secondary cooling zone is limited to the curved part where the slab surface temperature is 800°C or higher, so that sufficient electromagnetic stirring of the final solidified molten metal can be achieved and an excellent segregation elimination effect can be obtained. It is necessary for

3-charge low carbon aluminum-silicon killed steel manufactured by continuously melting Example 160 in a converter (components: 0.16% carbon, 0.3% silicon, 1.45% manganese, ribs, 018 %, sulfur 0.013%, remaining iron), the radius of curvature of 2 strands is 1
Each strand 240 was manufactured into a slab having a cross-sectional dimension of 190 mi x 1600 mm by continuously casting in a 0 m curved slab continuous casting machine at a casting temperature of 1540° C. and a drawing speed of 0.8 m /min.

At this time, by implementing the present invention, the first strand slab has a magnetic flux density of IK at a position corresponding to the center in the thickness direction of the slab.
G permanent magnets were placed at four locations 450 cm, 475 cm, 530 cm, and 560 CrrL away from the top of the mold as shown in Figure 3, and the 10th and 15th rollers from the top of the roller apron were energized. A brush was installed, and a DC current of 20 V and 5500 A was applied in the drawing direction to solidify the unsolidified portion while stirring.

The other second strand slab was solidified in the usual manner without electromagnetic stirring.

Then, a test piece was cut out from a point 10 m after the start of casting, and the sulfur print on the cross section and the component distribution in the thickness direction of the slab were examined, and the segregation situation at the center of the slab was investigated.

The results are shown in FIG. This Figure 4 shows the distribution of phosphorus in the thickness direction of the slab, where line A is a sample of the first strand slab according to the present invention, and line B is a sample of the second strand slab without electromagnetic stirring. This is the phosphorus distribution.

As is clear from this figure, in the case where electromagnetic stirring was not performed, there was a thick phosphorus segregation in the center.
It can be seen that there is almost no segregation overall in the electromagnetically stirred product according to the present invention.

[Brief Description of the Drawings] Fig. 1 is a perspective view showing the main parts of a curved continuous casting machine according to the present invention, Fig. 2 is a cross-sectional view of the permanent magnet installation part of the same, and Fig. 3 is a perspective view showing the main parts of a curved continuous casting machine according to the present invention. FIG. 4 is a perspective view showing the main parts of a curved continuous casting machine according to another embodiment, and a chart showing the phosphorus segregation situation in the slab. In the diagram, 1...Mold, 2...Slab, 3
...Roller, 4...Permanent magnet, 5...
...Electrifying brush, 6...Static magnetic field, 7.
...DC current, F...electromagnetic force, line A...
...Sample according to the implementation of this invention, line B...
Comparative sample.

Claims (1)

[Claims] 1. When pouring molten steel into a curved mold and pulling it out from the mold with a solidified shell formed on its outer surface for continuous casting with a single radius of curvature, the surface of the slab pulled out of the mold is at a high temperature of 800°C or higher. Permanent magnets are placed close to the slab surface between the slab guiding and supporting rollers on the upper and lower surfaces of the curved part, and have magnetic pole faces of opposite polarity facing each other, so that the main direction is the thickness of the slab. A static magnetic field is applied in the direction, a direct current is passed between the rollers located upstream and downstream of the permanent magnet, and the static magnetic field and the direct current cause an electromagnetic force to act in the width direction of the slab, and the inside of the slab is A method for electromagnetically stirring a slab in continuous casting, characterized by electromagnetically stirring the final solidified portion of the slab.