JP2937707B2 - Steel continuous casting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for continuously casting steel.

[0002]

2. Description of the Related Art As one of quality defects of steel sheets and the like, uniform properties cannot be maintained due to segregation of metal elements other than Fe in steel. In order to reduce such segregation in steel, S, P, etc. in steel are reduced and casting is performed. During casting, the composition is homogenized by electromagnetically stirring the slab unsolidified layer in a strand to reduce segregation. There are known methods of reducing the number of slabs and performing a light reduction treatment on the slab to reduce segregation.

[0003]

However, in the above-described method, a steel type which cannot reduce S, P, etc., or
In some cases, the cost load becomes too large to reduce P, S, etc., and in such a case, it cannot be applied, resulting in quality defects due to segregation. When the solidified layer becomes low temperature and becomes viscous, it becomes electromagnetically stirred, and it is difficult to prevent sufficient segregation.According to the further method, the position of the slab crater end varies depending on the casting conditions and becomes stable. It is difficult to satisfy the light reduction condition, and there is a disadvantage that segregation cannot be avoided reliably.

[0004] In addition to these difficulties, a constant amount of equiaxed crystals is generally generated in a slab during continuous casting, but various characteristics of a steel sheet are improved by forming only a columnar crystal in the slab. Therefore, it is required to produce columnar crystals reliably industrially.

[0005]

The continuous casting method for steel according to the present invention which has solved the above-mentioned problems is characterized in that the molten steel in the tundish is kept at 20 to 40 ° C. higher than the solidification temperature, The molten steel is continuously injected from the symmetrical position of the immersion nozzle disposed at the center of the continuous casting mold in the short side direction in the mold, and 200 to 60 from the injection position .
Casting is performed while applying a static magnetic field over the entire width in the long side direction within the mold below 0 mm to reduce segregation of metal elements in steel .

[0006]

Next, the method of the present invention will be described in detail with reference to the drawings. 1 and 2, an immersion nozzle 5 connected to a tundish 4 is arranged in a continuous casting mold 3 composed of a long side mold 1 and a short side mold 2, and supplied from the tundish 4 to the immersion nozzle 5. The molten steel 7 is continuously injected from the discharge ports 6, 6 a opened at symmetrical positions below the immersion nozzle 5 in the long side direction in the mold 3 and extracted as a slab 8.

[0007] Equiaxed crystals formed in the slab 8 are reduced,
In order to generate columnar crystals, it is necessary to maintain the temperature of the molten steel 7 injected into the mold 3 at a high temperature. In particular, when the injection of molten steel from the ladle (not shown) into the tangible 4 is at the end. The temperature of the molten steel in the TD 4 has dropped, and the molten steel 7 in the TD 4 is poured into the mold 3 and cast as a slab 8 to produce a solidified structure containing a certain amount of equiaxed crystals. become.

As described above, as a method for maintaining the molten steel 7 in the tan dash 4 at a high temperature, for example, the lid 10 is hung on the tan dash 4 in addition to being actively heated by a heating device 9 such as plasma heating or electric induction heating. By performing casting while preventing the temperature from decreasing due to heat radiation, for example, it is possible to reduce the equiaxed crystals and generate a solidified structure mainly composed of columnar crystals.

It is natural that the molten steel in the tundish 4 injected into the mold 3 is higher than the solidification temperature of the molten steel 7.
The temperature range must be maintained at 20 to 40 ° C. higher than the solidification temperature of the molten steel 7. The reason is that the temperature difference is 20
When the temperature is lower than 0 ° C, a solidified structure mainly composed of equiaxed crystals is not preferable, and even when the temperature difference is higher than 40 ° C, there is no particular problem in the formation of a columnar crystal solidified structure, but it takes a long time to cool. It takes time and the casting speed (slab slab pulling speed) must be reduced accordingly, which undesirably lowers productivity.

Further, molten steel 7 is fed from discharge ports 6, 6a provided at symmetrical positions of immersion nozzle 5 from the center of mold 3 to the inside of mold 3.
, The molten steel 7 injected into the casting mold 3 from the discharge ports 6 and 6a of the immersion nozzle 5 is divided into reverse flows 12 and 12a and descending flows 13 and 13a. Reference numerals 13 and 13a denote a portion which flows down to the unsolidified layer 14 in the width direction of the long side of the cast slab 8 to be drawn and reverses to an ascending flow. It becomes closer and generates equiaxed nuclei, which is not preferable for segregation .

By casting while applying a magnetic field with the static magnetic fields 11 and 11a over the entire width in the long side direction of the mold 3 below the injection position of the molten steel 7, the molten steel 7 is formed in an unsolidified portion above the magnetic body. It can be maintained in a high temperature state, and the generation of equiaxed crystals can be suppressed. On the other hand, a braking action acts on the descending flows 13 and 13a, and the descending speed of the descending flows 13 and 13a is rapidly reduced at the portion where the static magnetic field is applied. At the same time, in the unsolidified portion below this, the downflows 13 and 13a are almost uniformly rectified and flow down over the entire width of the slab 8 from which the downflows 13 and 13a are drawn, so that columnar crystals are generated in one direction.

The position at which the static magnetic field is applied is preferably 200 to 600 mm below the injection position of the molten steel 7 in the mold 3 (discharge nozzle discharge ports 6, 6a). That is, when the molten steel 7 is brought closer than 200 mm from the injection position, the falling speed of the descending flows 13 and 13a is rapid, so that it is difficult to reduce the effective speed due to the static magnetic field and to make uniform rectification in the long side width direction. And 6
When a static magnetic field is applied below the molten steel injection position exceeding 00 mm, it becomes difficult to maintain the molten steel at a high temperature in an unsolidified portion above the magnetic field zone. Further, the magnetic flux density of the static magnetic field is generally in the case of a slab thickness of 220 to 250 mm.
0.1 to 0.5T is sufficient.

The slab continuously cast as described above can be subjected to light reduction in the strand to prevent the solidification shrinkage flow at the end of solidification.

[0014]

【Example】

1) Molten steel composition C: 0.16%, Mn: 1.00%, Si: 0.25
%, P: 0.02%, S: 0.01%, Al: 0.05
% Residual impurities and Fe. 2) Casting conditions (1) Cast size: 1200 mm long side, 245 mm short side. (2) Immersion nozzle shape: inner diameter 90 mm, discharge port diameter 70 m
m, discharge angle downward 45 ° (2-hole type). (3) Immersion nozzle depth: 200 mm (meniscus to upper end of discharge port). (4) Static magnetic field position: 450 mm (distance between meniscus and coil center).

[Table 1] Note 1 The molten steel heating temperature is the temperature of the molten steel in the tundish minus the solidification temperature. Note 2 polarized析評point, polarized析最large particle size which occurs billet C cross-section. Note 3 All equiaxed crystal ratios are evaluated in terms of L-plane equiaxed crystal ratio. Note 4 In all of the examples, the molten steel was injected into the mold by a tundish plasma heating device while maintaining the degree of heating of the molten steel at a high temperature. As shown in Table 1, in Examples of the present invention, a columnar crystal-based structure was achieved, and a good material could be achieved. In contrast, the comparative example has assumed a high polarization析評point.

[0015]

According to the method of the present invention, F in steel (product)
Segregation of metal elements other than e can be reliably reduced,
Various properties such as tensile strength, bending workability, and stretch formability of the steel material can be improved. Further, the crystals in the steel are mainly composed of columnar crystals, and from this point, the above-mentioned various properties can be advantageously satisfied. Furthermore, many excellent effects can be obtained such as industrially stable casting. Therefore, the present invention has a large contribution to the development of the industry as a solution to the problems of the conventional continuous casting method for steel.

[Brief description of the drawings]

FIG. 1 is a side sectional view for explaining one embodiment of the method of the present invention.

FIG. 2 is a plan view illustrating an embodiment of the method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Long side mold 2 Short side mold 3 Mold 4 Tandish 5 Dip nozzle 6 Dip nozzle discharge port 6a Dip nozzle discharge port 7 Molten steel 8 Cast piece 9 Heating device 10 Lid 11 Static magnetic field 11a Static magnetic field

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-284750 (JP, A) JP-A-54-14334 (JP, A) JP-A-6-15420 (JP, A) JP-A-2-284 11252 (JP, A) JP-A-59-147756 (JP, A) JP-A-7-100607 (JP, A) JP-A-4-274849 (JP, A) JP-A-4-104251 (JP, U) (58) Field surveyed (Int. Cl. ⁶ , DB name) B22D 11/10 350 B22D 11/10 310 B22D 11/04 311

Claims (1)

(57) [Claims] 1. The molten steel in a tundish is set at a temperature of 20
Maintained at to 40 ° C. hot, then the molten steel continuously injected from symmetrical positions of the immersion nozzle disposed in the central portion of the continuous casting in a mold to the short side of the mold, 2 from the injection position
Casting while applying a static magnetic field over the entire width in the long side direction in the mold below 00 to 600 mm , segregation of metal elements in steel
A method for continuous casting of steel, characterized in that it is reduced .