KR20100005235A - Continuous casting method of steel - Google Patents

Abstract

[PROBLEMS] To materialize an applying mode of current to a shared coil. [MEANS FOR SOLVING PROBLEMS] An electromagnetic coil having two exciting coils (5b) wound to peripheral parts of two magnetic pole cores (5a) and one exciting coil (5c) wound to a peripheral part obtained by combining the two magnetic pole cores (5a) is arranged by the same number on peripheries of respective long sides (3b) of a cast (3), namely, (2n+2)-pieces ((n) is natural number) in a periphery total of the long sides (3b) In the case of electromagnetic stirring, polyphase AC current whose current phase difference is 90 degrees to 120 degrees and which has three phases or above is conducted to the exciting coils (5b and 5c) of all the electromagnetic coils. In the case of an electromagnetic brake, DC current is conducted to the exciting coil (5c) or the three exciting coils (5b and 5c) per electromagnetic coil so as to continuously cast steel. The electromagnetic brake or electromagnetic stirring is selectively operated in accordance with a component composition and an amount of molten steel (2) supplied to the cast (3). [Effects] A cast piece with sufficient surface quality can stably be obtained irrespective of a steel type and a cast condition, occurrence of brake-out can be suppressed and a stable operation is realized.

Description

Continuous casting method of steel {CONTINUOUS CASTING METHOD OF STEEL}

TECHNICAL FIELD This invention relates to the method of continuously casting steel, controlling the flow of molten steel in a mold using the electromagnetic coil apparatus which can selectively operate an electromagnetic brake and electromagnetic stirring.

In continuous casting of general steel, molten steel is hot-watered in a mold using the immersion nozzle which has two discharge holes. FIG. 2: is a longitudinal cross-sectional view which shows typically the flow state of molten steel in the mold in this general continuous casting method. FIG. The molten steel 2 emerging from the discharge hole 1a of the immersion nozzle 1 collides with the solidification shell 2c on the short side 3a of the mold 3, and then the upstream 2a and the downflow 2b. Branch to The upward flow 2a among these becomes a horizontal flow toward the immersion nozzle 1 under meniscus. In addition, 4 in FIG. 2 shows mold powder.

Flow control of molten steel in this casting mold is very important in terms of operation and quality control of casting pieces. As a method of realizing the flow control of this molten steel, there exist a method of devising the shape of an immersion nozzle, the method of applying an electromagnetic force to the molten steel in a mold, etc. In recent years, among these methods, the method which makes an electromagnetic force act on molten steel became widely used. There are two methods of applying the electromagnetic force to the molten steel: an electromagnetic brake for applying a braking force to the molten steel discharged from the immersion nozzle, and an electromagnetic stirring for stirring the molten steel by the electromagnetic force.

The electromagnetic brake and the electromagnetic stirring have advantages and disadvantages, respectively, but in general, the electromagnetic brake is used at the time of high speed casting, and the electronic stirring is used at the time of low speed casting. Both of these electromagnetic brake apparatuses and electromagnetic stirring apparatuses are provided with the electromagnetic coil which wound the coil in the iron core in the back surface of the copper plate of a mold. The apparatus which has these electromagnetic coils normally has only the independent function which is either an electromagnetic brake function or an electromagnetic stirring function.

Therefore, in the past, the development of the electromagnetic coil apparatus (henceforth a dual coil) which can selectively operate an electromagnetic brake and electromagnetic stirring is performed, and the applicant has proposed patent documents 1 and 2. As shown in FIG.

[Patent Document 1: Japanese Patent Laid-Open No. 2005-349454]

[Patent Document 2: Japanese Patent Application Laid-Open No. 2007-007719]

The dual purpose coils of Patent Documents 1 and 2 selectively operate an electromagnetic brake or electromagnetic stirring on molten steel in the mold by supplying a direct current or alternating current to the electromagnetic coil disposed on the outer circumference of the mold.

The combined coil proposed in these patent documents 1 and 2 enables the combined use of an electromagnetic brake and electromagnetic stirring, which has not been possible in the past.

Problems to be Solved by the Invention

The problem to be solved by the present invention is that it is not clear how the current should be applied when continuously casting steel in the case of the combined coil which enables the application of both functions of the electromagnetic brake and the electronic stirring proposed by the applicant. Is that.

Means for solving the problem

The continuous casting method of the steel of the present invention,

To specify the state of application of the current to the combined coil,

An electronic coil having two magnetic pole cores, two excitation coils wound around each outer peripheral portion of the magnetic pole cores, and one excitation coil wound around the outer peripheral portion where the two magnetic pole cores are combined, the same on each long side on the outer periphery of the mold long side In number, we arrange (2n + 2) number (n is natural number) in the outer circumference total of the mold long side,

In the case of electromagnetic stirring of the molten steel in the mold, a current of the phase difference is applied to each of the excitation coils in all the electromagnetic coils.

In the case of applying the electromagnetic brake to the molten steel in the mold, a DC current is applied to one of the excitation coils wound around the outer periphery of the two magnetic pole cores for each electromagnetic coil, or a DC current is applied to these three excitation coils. Is a method of continuously casting steel by energizing

The main feature is to selectively actuate the electromagnetic brake or the electromagnetic agitation in response to the component composition of the molten steel and the amount of the hot water supplied to the mold.

More specifically,

When the component carbon concentration of the molten steel supplied to the mold is in mass%, 0.07% or more and 0.16% or less,

When the hot water supply amount is less than 3 ton / min, the three-phase or more multi-phase alternating current is applied to the electromagnetic coil in order to apply electromagnetic stirring to the molten steel in the mold.

When the hot water supply amount is 3 ton / min or more, the direct current is applied to the electromagnetic coil in order to apply the electromagnetic brake to the molten steel in the mold.

Moreover, when the component carbon concentration of the said molten steel supplied to a mold exceeds 0.0050% by mass%, and is less than 0.07%,

When the hot water supply amount is less than 4 ton / min, the three-phase or more multi-phase alternating current is applied to the electromagnetic coil in order to apply electromagnetic stirring to the molten steel in the mold.

When the hot water supply amount is 4 ton / min or more, the direct current is applied to the electromagnetic coil in order to apply the electromagnetic brake to the molten steel in the mold.

Moreover, when the component carbon concentration of the said molten steel supplied to a mold is 0.0050% or less in mass%,

When the hot water supply amount is less than 5 ton / min, the three-phase or more multi-phase alternating current is applied to the electromagnetic coil so as to cause electromagnetic stirring to the molten steel in the mold.

When the hot water supply amount is 5 ton / min or more, the direct current is applied to the electromagnetic coil in order to apply the electromagnetic brake to the molten steel in the mold.

Effect of the Invention

According to the continuous casting method of steel of this invention, even if steel grade and casting conditions change, the casting piece with favorable surface quality can be obtained stably. In addition, the occurrence of breakout can be suppressed, thereby enabling stable operation.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure explaining the shape of the combined coil used for the method of this invention, (a) is a horizontal cross section, (b) is a vertical cross section.

FIG. 2: is a longitudinal cross-sectional view which shows typically the flow state of the molten steel in casting in the general continuous casting method. FIG.

<Explanation of symbols for the main parts of the drawings>

1: immersion nozzle 2: molten steel

3: mold 3a: short side

3b: long side 5: combined coil

5a: Teeth part 5b: Inner winding

5c: outer winding 5d: core

According to the present invention, the component composition and the amount of hot water supply of molten steel for hot water supplying the mold with the current applied to the dual purpose coil in the continuous casting of the steel using the dual purpose coil which enables the dual function of the electromagnetic brake and the electronic stirring. In response.

Example

EMBODIMENT OF THE INVENTION Hereinafter, the best form for implementing this invention with the process from the idea of this invention to the solution of a subject is demonstrated using FIG.

The inventors examined how to apply electromagnetic brake or electromagnetic stirring selectively to casting conditions in the continuous casting of steel using the dual-use coil of patent document 2.

The electromagnetic brake has the effect of suppressing longitudinal cleavage due to non-uniform solidification, suppressing re-dissolution of the solidification shell, and suppressing occurrence of breakout. This is because the molten steel flow rate discharged from the immersion nozzle is lowered and the molten steel flow rate colliding with the solidification shell is lowered.

On the other hand, electromagnetic stirring increases the molten steel flow rate under the meniscus by imparting molten steel parallel to the solidification shell, and prevents bubbles and inclusions from being trapped by the solidification shell, and thus is effective in preventing surface defects of the cast pieces. have.

The inventors investigated by varying the carbon concentration, which is the basic component of steel, and the amount of hot water supply to the mold determined by the casting speed and the mold cross-sectional area when selectively acting on the electromagnetic brake or the electronic stirring according to the casting conditions. The reason why the rate of hot water supply is defined without the casting speed as a parameter is that the discharge flow rate from the immersion nozzle is a main parameter of the molten steel flow in the mold, and is more suitable as a parameter for determining the method of flow control of the molten steel than the drawing speed. Because.

Hereinafter, the investigation result which the inventors performed is demonstrated.

The molten steel which has a chemical composition shown in following Table 1 was cast by the vertical bending continuous casting machine which can manufacture the casting piece of width 1500mm and thickness 270mm.

Table 1

The combined coil used for casting in FIG. 1 and its typical dimension are shown together. 5 in FIG. 1 is the two combined coils which were arrange | positioned continuously in the long side 3b side of the mold 3, respectively, the winding 5b is performed to each of the two tooth parts 5a, and the two tooth parts 5a Winding 5c is performed outside and is combined into one. In addition, 5d shows the core which made the upper end the same height as the meniscus, and 6 shows the backup plate provided in the outer side of the mold 3.

Moreover, the specification of the combined coil which has both the functions of an electromagnetic brake and electromagnetic stirring is shown below. In addition, casting conditions are shown in Table 2 below, and the casting results are shown in Table 3 below.

(Specification of combined coil)

Electromagnetic force in thickness direction center part of mold: 3000Gauss

Frequency: 4.0Hz

Current applied to each excitation coil: 45000 ampere turn

Phase of AC current: Three phase AC of 120 degrees phase

Table 2

Table 3

The steel grade A group is a low carbon aluminum killed steel having a carbon concentration of more than 0.0050% and less than 0.07% by mass%, so that non-uniform solidification hardly occurs, and the inspection reference level of the surface defects of the cast pieces is not high. Therefore, casting was possible even at a high speed with a hot water supply amount of 5.7 ton / min without applying electromagnetic brake or electromagnetic stirring (Comparative Example 23).

However, when the electromagnetic brake was not operated, the breakout occurrence rate increased when the amount of hot water became 4 ton / min or more (Comparative Examples 22 and 23). On the other hand, when the amount of hot water supply was less than 4 ton / min, when the electronic stirring was not effected, surface defects of the cast pieces were frequent (Comparative Example 21).

On the other hand, when the amount of hot water supply was 4 ton / min or more, stable casting could be realized by applying an electromagnetic brake (Examples 2 to 4 and 14). Moreover, when the amount of hot water supply was less than 4 ton / min, the rate of occurrence of surface defects of the cast pieces decreased by applying electronic stirring (Examples 1 and 13).

The steel grade B group is a very low carbon steel whose carbon concentration is 0.0050% or less in mass%, and it is hard to produce nonuniform solidification, but the inspection reference level of the surface defect of the casting piece is very high. When the magnetic stirring and the electromagnetic brake were not applied, even when the hot water supply amount was less than 5 ton / min, a surface defect occurred on the casting piece (Comparative Example 24), and when the hot water supply amount was 5 ton / min or more, the surface defects of the casting piece were frequent. (Comparative Example 25).

In this steel grade B group, when hot water supply amount is less than 5 ton / min, it is effective to make electromagnetic stirring effective, and the effect was especially large (Examples 5-7 and 15). Moreover, it was also effective to apply an electromagnetic brake when the hot water supply amount is 5 ton / min or more (Examples 8 and 16).

The steel grade C group is an apocrystal steel whose carbon concentration is 0.07% or more and 0.16% or less in mass%, and it is easy to produce nonuniform solidification, and the inspection reference level of surface defects is low. In this steel grade C group, when electromagnetic stirring and electromagnetic brake were not applied, when the hot water supply amount was 4 ton / min or more, splitting and re-dissolution occurred, and the occurrence rate of breakout was very high (Comparative Examples 27 and 28).

In this steel grade C group, when the hot water supply amount is less than 3 ton / min, electromagnetic stirring is applied (Example 17), and when the hot water supply amount is 3 ton / min or more, the electromagnetic brake is applied (Examples 9 to 12 and 18). The breakout incidence rate can be reduced.

As a result, in the case of low carbon steel, when the hot water supply amount is 4 ton / min or more, in the case of ultra low carbon steel, when the hot water supply amount is 5 ton / min or more, and in the case of apojeong steel, when the hot water supply amount is more than 3 ton / min, the electromagnetic brake is large. It worked. In particular, in the apocrystal steel where nonuniform solidification and re-dissolution of a solidification shell are easy to generate | occur | produce, the electromagnetic brake exhibited the very big effect.

On the other hand, when hot water supply amount was less than the said value in the said steel grade, electronic stirring showed the big effect. Especially in the ultra low carbon steel, although the inspection reference level is high, the incidence rate of the surface defects of the cast pieces is high, and a large effect is obtained by applying electron agitation.

It goes without saying that the present invention is not limited to the above-described examples, and may change the embodiment as appropriate as long as it is a scope of the technical idea described in each claim.

For example, the alternating current may not be three-phase, or may be higher if the current phase difference is 90 degrees to 120 degrees.

As long as the present invention is continuous casting, any type of continuous casting such as a curved type and a vertical type can be applied. In addition, the present invention can be applied not only to continuous casting of slabs but also to continuous casting of frames.

Claims (4)

An electronic coil having two magnetic pole cores, two excitation coils wound around each outer peripheral portion of the magnetic pole cores, and one excitation coil wound around the outer peripheral portion where the two magnetic pole cores are combined, the same on each long side on the outer periphery of the mold long side In number, we arrange (2n + 2) number (n is natural number) in the outer circumference total of the mold long side, In the case of electromagnetic stirring of the molten steel in the mold, each exciting coil in all the electromagnetic coils is energized with a three-phase or more polyphase alternating current having a current phase difference of 90 degrees to 120 degrees, In the case of applying the electromagnetic brake to the molten steel in the mold, a DC current is applied to one of the excitation coils wound around the outer periphery of the two magnetic pole cores for each electromagnetic coil, or a DC current is applied to these three excitation coils. Is a method of continuously casting steel by energizing A method of continuously casting steel, characterized by selectively acting on electromagnetic brake or electromagnetic stirring in response to the component composition of the molten steel and the amount of hot water supplied to the mold. The method according to claim 1, When the component carbon concentration of the molten steel supplied to the mold is in mass%, 0.07% or more and 0.16% or less, When the hot water supply amount is less than 3 ton / min, the three-phase or more multi-phase alternating current is applied to the electromagnetic coil in order to apply electromagnetic stirring to the molten steel in the mold. When the hot water supply amount is 3 ton / min or more, the direct current is applied to the electromagnetic coil in order to apply the electromagnetic brake to the molten steel in the mold. The method according to claim 1, When the component carbon concentration of the molten steel supplied to the mold is, in mass%, more than 0.0050% and less than 0.07%, When the hot water supply amount is less than 4 ton / min, the three-phase or more multi-phase alternating current is applied to the electromagnetic coil in order to apply electromagnetic stirring to the molten steel in the mold. When the hot water supply amount is 4 ton / min or more, the direct current is applied to the electromagnetic coil in order to apply the electromagnetic brake to the molten steel in the mold. The method according to claim 1, When the component carbon concentration of the molten steel supplied to the mold is 0.00% by mass or less, When the hot water supply amount is less than 5 ton / min, the three-phase or more multi-phase alternating current is applied to the electromagnetic coil so as to cause electromagnetic stirring to the molten steel in the mold. When the hot water supply amount is 5ton / min or more, the direct current is applied to the electromagnetic coil in order to apply the electromagnetic brake to the molten steel in the mold.

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