JPS5813263B2 - Continuous casting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is characterized by a stirring method for a continuous casting method in which the unsolidified portion of a slab is solidified while being stirred by the thrust generated by the interaction between the magnetic force of a permanent magnet and an electric current during continuous casting. Concerning continuous casting method.

Segregation areas enriched with carbon, sulfur, phosphorus, etc. are likely to occur in the center of slabs manufactured by continuous casting.

The macrostructure of this segregated area exhibits a color tone different from that of the normal area, and products made from this slab have the disadvantage that their mechanical properties and commercial value are significantly reduced.

It is known that the above-mentioned center segregation can be reduced by producing a large number of equiaxed crystals in the center of the slab, and one proposed method for this is to stir the unsolidified molten metal inside the slab during solidification of the slab. has been done.

The conventional method of stirring unsolidified molten metal is to apply a rotating or moving magnetic field to the continuously cast slab during solidification, and apply a thrust in the moving direction of the magnetic field to the unsolidified portion inside the slab. However, as schematically shown in Figure 1, electromagnetic stirring is basically based on a unidirectional flow in the width direction of the slab. When stirring is carried out in a circular flow above and below the slab (Fig. 1a), the unsolidified molten metal near the solidified shell of the transverse cross section of the slab is stirred in a circular shape by countercurrents that apply electromagnetic forces in opposite directions. In the case of flowing and stirring (Fig. 1b), and in the case where multiple stirring devices are arranged in the casting direction and the direction of electromagnetic force of each stirring device is opposite to each other, the stirring is performed by flowing in an S shape in the casting direction. (Fig. 1C).

However, when unsolidified molten metal is solidified while stirring,
In the region solidified under stirring, all solute components are negatively segregated and the sulfur print appears white, so this region is generally referred to as the white band.

The concentration of this white band varies depending on the flow rate of the molten metal, and as the flow rate increases, the whiteness becomes more noticeable.

Therefore, if the flow velocity is uneven, the appearance of the white band will vary from place to place, which is unfavorable in terms of the macro pattern.

Therefore, in order to make the white band uniform, it is necessary to keep the flow rate of the molten metal constant by electromagnetic stirring.

However, in the cases shown in FIGS. 1A and 1C, the flow caused by stirring forms a loop with a long path, so the flow velocity varies greatly depending on the location.

Therefore, the white band varies depending on the location and significantly impairs the macro pattern.

Further, in the case shown in FIG. 1b, the flow due to stirring has a circular shape, and the white band appears almost uniformly.

However, placing the stirring devices facing each other and applying forces in opposite directions is not preferred as a stirring method because the magnetic fields are partially canceled out in the thickness direction of the slab, resulting in poor electromagnetic efficiency.

In order to eliminate the above-mentioned drawbacks of the conventional method, the present invention proposes a continuous casting method in which a flow of unsolidified molten metal is formed through small loops by stirring to make the white band uniform and to reduce the degree of the white band. It is something.

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

FIG. 2 shows the main parts of a curved continuous casting machine, in which 1 is a mold, 2 is a slab, and 3 is a roller forming a roller apron.

Permanent magnets 4 are placed between the rollers at required locations in this roller group.
will be established.

Although the figure shows a case where four locations are installed in the casting direction, the number of locations can be changed arbitrarily.

As shown in FIG. 3, this permanent magnet 4 is designed to accommodate the width of the slab 2 so that a small loop with a loop width L of 400 mm or less is formed when the molten metal is stirred by thrust. A plurality of permanent magnets are arranged in series across the entire direction, with the N and S poles of each permanent magnet facing and close to the surface of the slab, and further placed on both sides with the slab 2 in between. The opposing permanent magnets 4 are provided so that their magnetic poles are opposite to each other.

The reason why the loop width L was limited to 400 strokes or less was based on the results of many experiments by the inventors.

In other words, as mentioned above, generally speaking, as the loop diameter increases, the white band becomes uneven, but we determined through experiments that the limit of non-uniformity in the width direction of the white band that is acceptable as a product is 400 mm. It turned out that the following.

On the other hand, the upper rollers 7, 7 facing the uppermost magnet of the permanent magnet group arranged as described above and the lower rollers 8, 8 facing the lowermost magnet have brushes 6, 6, 9, respectively.
, 9 are provided, each brush is connected to a DC power supply circuit 10, and as shown in FIG.
The molten metal is configured to flow from the unsolidified molten metal of the slab 2 to the reroller 8 and the brush 9.

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.

The permanent magnet has a residual magnetic flux density Br5~10KG, a coercive force Hc5~10KOe, and a maximum energy product [BrHc]
The one with larger max is suitable, YCo5, CeCo
5. Rare earth cobalt a-stone having components such as SmCo5 and SmPrCo5 is optimal.

When continuous casting is performed using this device, the slab 2 that has been pulled out of the mold 1 and is in the process of solidifying at the roller apron is exposed to a magnetic field 5 whose main direction is perpendicular to the drawing direction by the opposing permanent magnets 4, as shown in FIG. acts.

On the other hand, when the DC circuit is energized, a direct current acts inside the slab in the same direction as the direction in which the slab is pulled out, and a synergistic effect with the magnetic field 5, so-called Fleming's left-hand rule, causes a direct current to act inside the slab. An electromagnetic force F in the width direction of the slab acts on the unsolidified molten metal.

In this case, since the plurality of permanent magnets are arranged so that the directions of the magnetic fields 5 are alternately opposite, the electromagnetic force F acts alternately in opposite directions in the slab width direction.

The molten metal therefore moves in small flow loops.

This flow loop can be made smaller by increasing the number of magnetic poles of the permanent magnet installed.

In addition, when permanent magnets 4 are arranged at four locations in the drawing direction of the slab as shown in Fig. 4, as shown in Fig. 5, the electromagnetic force F1 of the two sets of permanent magnets arranged above and below is If F2 is configured to act in opposite directions, a thrust force f that partially rotates will be generated therebetween.

Since this thrust force f is generated in each part as shown by the solid arrow in Fig. 5, the unsolidified molten metal forms many small loops in the drawing direction, and the whole is stirred while partially convecting, causing segregation in the center of the slab. will be resolved.

Furthermore, the thrust f that causes the molten metal to flow can be changed by changing the strength of the direct current or magnetic field.

Therefore, in the embodiment shown in FIG. 4, if the strength of the permanent magnet 4 is changed in the order of weak → strong → weak → strong from above to change the arrangement and flow strength, the boundary of the white band will become unclear. At the same time, equiaxed crystals can be grown.

The reason is that the strength of the magnetic field is 0. When the temperature exceeds 6 KG, the number of equiaxed crystals increases rapidly, but at the same time, the degree of negative segregation gradually becomes significant, which is not preferable.

This is because the above-mentioned defects can be removed by alternately changing the strength of the magnetic field.

Example 1 3-charge low carbon aluminum silicon killed steel continuously melted in a 160t converter (components: 0.16% carbon, 0.3% silicon, 1.45% manganese, 0.018% phosphorus) , 0.013 iron remaining) was continuously cast in a two-strand curved slab continuous casting machine at a casting temperature of 1540°C and a drawing speed of 0.8 m/min, with cross-sectional dimensions of 190 mm x 1600 mm. Each strand is made of 240 pieces of slab.
t manufactured.

At this time, by implementing the present invention, the first strand slab has a magnetic flux density of 1.0 at the center in the thickness direction of the slab. 0KG
Then, permanent magnets (SmCo5) arranged so that two sets of N poles and two S poles were arranged alternately in the width direction of the slab were placed at 450 cm, 475 cm, 530 cm, and 560 cm from the top of the mold.
They were placed in four separate locations as shown in Figures 3 and 4, and energizing brushes were installed on the 10th and 15th rollers from the top of the roller apron, with a voltage of 20 V in the pulling direction.
A direct current of 5500 A was applied to solidify the unsolidified portion while stirring.

The slab of the other second strand is placed close to the slab surface as shown in Fig. 6a, using a stirring device with a north pole on one surface and a south pole on the other surface, as described above. It was cast under the same conditions.

After the start of casting, 20 m, 50 m,
A test piece was cut out from a 80 m point, and the cross section was sulfur printed, and the component distribution in the area solidified under stirring in the width direction of the slab (the so-called white band area) was investigated to investigate the uniformity of that area. .

The results are shown in FIG.

This Figure 7 shows the distribution of phosphorus. Curve A is a sample of the first strand slab according to the present invention, and curve B is a sample of the second strand slab stirred by one loop of flow. is the distribution curve of

As is clear from this figure, there is a large difference in phosphorus content between the samples stirred by one-loop flow, and a white band (conspicuous when the phosphorus content is around 0.011% or less) is present, clearly indicating negative segregation. On the other hand, in the case of implementing the present invention, the content is almost uniform throughout the width direction of the slab, and the white band is reduced to the extent that it is almost invisible on the sulfur print.

Example 2 In the same continuous casting machine as in Example 1, the strength of the permanent magnets was changed from top to bottom, and the magnetic flux density at the center in the thickness direction of the slab was 0.2.
KG, 0.6KG, 0.5KG, and 1.0KG were cast under the same conditions.

As a result, it was confirmed that the degree of negative segregation decreased and the white band on the sulfur print was almost invisible.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram schematically showing the flow of molten metal during electromagnetic stirring of unsolidified molten metal of a conventional continuously cast slab, and Fig. 2 shows the main parts of a curved continuous casting machine according to the present invention. Figure 3 is a cross-sectional view of the same magnet installation part, Figure 4 is a perspective view.
The figure is an explanatory diagram showing a DC circuit, Figure 5 is an explanatory diagram showing the convection situation of unsolidified molten metal inside a slab, and Figure 6 is a stirring method using the conventional method to create one loop of flow in the width direction of the slab. FIG. 7 is a chart showing the phosphorus segregation situation in the slab. In the figure, 1...Mold, 2...Slab, 3...Roller, 4...
Permanent magnet, 5...Magnetic field, 6,9...Brush, 7,8...
Roller, 10...DC power supply circuit, A...Distribution curve showing the phosphorus content of the slab stirred by implementing the present invention, B...
...Similarly, the distribution curve in the case of the conventional method, F...Electromagnetic force, f...Thrust force.

Claims (1)

[Claims] 1. In continuous casting, in the secondary cooling zone where an unsolidified portion exists inside the slab, a magnetic field is formed in the unsolidified portion by a permanent magnet, and an electric current is passed through the slab, thereby The continuous casting method uses the generated thrust to solidify the unsolidified portion while agitating the unsolidified portion. A continuous casting method that makes the component distribution uniform in the width direction and reduces white bands. 2. In continuous casting, in the secondary cooling zone where an unsolidified portion exists inside the slab, a permanent magnet forms a magnetic field in the unsolidified portion, and an electric current is passed through the slab, and the thrust generated thereby cools the unsolidified portion. In the continuous casting method, which solidifies while stirring, at multiple positions at different distances from the top of the mold,
The loop diameter L of the unsolidified part of the slab in the width direction of the slab is 400 m.
By forming a plurality of small flow loops of less than m in diameter and making them flow in opposite directions, and by making the flow directions in the upper and lower positions opposite to each other, the unsolidified slab is Continuous casting characterized by forming a plurality of small vertical loops in a part and solidifying it while stirring, making the component distribution uniform in the width direction of the slab in the white band part, and reducing the white band itself. Law.