JPH11239851A - Method for controlling flow in mold for wide width and thin and middle thickness cast slab - Google Patents

Abstract

PROBLEM TO BE SOLVED: To carry out the stable casting while controlling the flow in a mold, particularly at the time of casting at a low speed by changing impressing direction of electromagnetic force acted to molten steel in the mold according to the level of the casting speed. SOLUTION: Based on a reference value of the casting speed, the impressing direction of the electromagnetic force is changed so that the molten steel flow from an immersion nozzle 1 is decelerated in the case of being the reference value or higher, and the molten steel flow is accelerated in the case of being less than the reference value, and the casting is executed. The molten steel poured into the mold 2 from the immersion nozzle 1 forms a spouting flow 4 toward the short wall 3 side and this spouting flow 4 collides against the short wall 3 surface and divides into the ascending flow 5 and the descending flow 6. The ascending flow 5 becomes the ascending flow 8 toward the immersion 1 direction near the molten steel surface 7. The spouting flow 4 toward the short wall 3 side is decelerated with the action of the electromagnetic force impressed with an electromagnetic coil 9 arranged so as to circulate the back surface of the mold 2. Therefore, the ascending flow 5 toward the molten steel surface 7 direction is also decelerated, and the variation of the molten steel surface in the mold is restrained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the flow of a wide, thin, and medium-thick slab in a continuous casting of a wide, thin, and medium-thick slab.

[0002]

2. Description of the Related Art In recent years, the remarkable progress in refining and casting techniques has facilitated the production of cast slabs having good quality properties, and has increased the concept of energy saving and energy saving. Attempts to directly and continuously produce thin slabs from molten metal without significant omission or hot rolling have been made not only for nonmetals with relatively low melting points but also for iron-based metals .

[0003] As means for continuously casting this thin slab, the following methods have been proposed. (1) A continuous casting method using a belt-type moving wall mold. (2) A continuous casting method using a modified cross-section mold (SMS method). (3) Twin roll continuous casting method.

[0004] However, the above method has the following problems. In other words, the continuous casting method (1) has the problem of high maintenance cost and running cost due to the difficulty of cooling the belt, and also has the problem that the immersion nozzle, which tends to be very difficult to dispose in this type of mold, There is a problem that it is very difficult to maintain surface quality unless casting is performed. In the continuous casting method of the above (2), a large frictional force is generated between the inner surface of the mold and the surface of the slab because the cross-sectional area in the mold decreases gradually but in the casting direction. It has been pointed out that the inner surface is severely worn and the life of the mold is shortened. the above
The continuous casting method (3) has a problem that the flow of the molten metal is severe when the roll is rolled down in the unsolidified portion, so that the floating separation of inclusions is difficult, and segregation is liable to occur.

[0005] As described above, the conventional continuous casting method for thin slabs has many unsolved problems from the viewpoint of stably producing thin slabs of satisfactory quality under good workability. In particular, it has not reached the level where it can be replaced with the conventional method involving hot rolling in the industrial production of iron-based sheet metal materials.

The present inventors have proposed, as an alternative,
A high-speed casting method of medium-thick slab having a mold thickness of about 90 to 120 mm has been proposed. Further, in Japanese Patent Application Laid-Open No. 8-90187, a so-called non-solid A continuous casting method with solidification pressure was proposed.

[0007]

In the continuous casting method for wide and thin / medium-thick cast slabs, high-speed casting is essential from the viewpoint of securing the production amount, and the casting speed is usually 3 m / min or more. For stable operation of high-speed casting, it is particularly important to control the level of the molten metal. An electromagnetic brake (EMBr) is provided on the back of the mold, and the discharge flow from the immersion nozzle (SEN) is decelerated by electromagnetic force to reduce the molten metal in the mold. Reduction of surface fluctuation has been performed.

However, it has been found that the following problems occur when the casting speed is reduced due to operational problems in the upper and lower steps. (1) Since the thickness of the mold is as thin as 90 to 120 mm, the distance between the SEN and the inner wall of the mold is small, and the flow of molten steel in this part is reduced. Is easy to occur.

(2) In particular, when the SEN has a flat shape, there is a wide range of portions where the distance between the inner wall of the mold and the SEN is small, and the above-mentioned problem (1) becomes remarkable. (3) When the unsolidification reduction is performed, even if the casting speed is the same, the molten steel injection amount is reduced, so that the flow in the mold is reduced, and the tendency of the above (1) is strengthened. (4) When the surface of the molten metal becomes skinned, there is a possibility that poor slagging of the powder is caused to cause vertical cracks and breakout.

[0010] An object of the present invention is to respond to a change in casting speed,
In particular, it is an object of the present invention to provide a method for controlling the flow in a mold of a wide, thin and medium-thick cast slab which enables stable casting by controlling the flow in the mold during low-speed casting.

[0011]

Means for Solving the Problems The inventors of the present invention have proposed a wide and thin film.
The knowledge that stable casting is possible by promoting technology development for stable casting of medium thickness slabs and changing the direction of application of electromagnetic force acting on molten steel in the mold according to the casting speed level I got That is, as described above, in the casting of wide, thin and medium-thick cast slabs, when the casting speed is reduced due to an operation trouble or the like, the surface of the molten metal surface is generated and the operation becomes unstable. This instability of the operation occurs when the casting speed falls below a reference value set by the slab size.
It is improved by applying an electromagnetic force to accelerate the molten steel flow from N.

The gist of the present invention is based on the above-mentioned findings. The gist of the present invention is that “in continuous casting of wide, thin and medium-thick cast slabs, the casting speed is based on a reference value of casting speed. The method of controlling flow in a mold of a wide, thin, and medium-thick cast slab is characterized in that casting is performed by changing the direction of application of electromagnetic force so as to accelerate the molten steel flow if the flow rate is less than a reference value. .

In the above, the term "wide and thin / medium thick slab" refers to an outlet of a continuous casting machine having a width of about 800 to 1800 mm and a thickness of about 50 to 120 mm. The reference value of the casting speed is, for example, the thickness × width of the slab is 12000.
If less than about 0 mm ^2, about 2.5 to 3.0 m / min, 12
The value is set in the range of about 2.0 to 2.5 m / min for about 0000 mm ² or more. The method of the present invention is particularly suitable for continuous casting in which a slab having an unsolidified layer is rolled down with a roller apron band.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The method of the present invention is based on the reference value of the casting speed in continuous casting of wide, thin and medium-thick cast slabs. If the value is less than the above range, the casting is performed by changing the application direction of the electromagnetic force so as to accelerate the molten steel flow.

The high-speed casting and the low-speed casting used in the following description refer to the case where the casting speed is equal to or higher than the reference value and lower than the reference value, respectively. FIG. 1 is a longitudinal sectional view of the upper part of a mold schematically showing a flow pattern in the mold at the time of high-speed casting of the present invention.

As shown in FIG. 1, the molten steel injected from the SEN 1 into the casting mold 2 forms a discharge flow 4 toward the short side 3, which collides with the short side surface and forms an upward flow 5. And a downward flow 6. The upward flow 5 becomes an upper layer flow 8 in the direction of SEN1 near the molten metal surface 7. Discharge flow 4 toward short side 3
Is decelerated by the action of the electromagnetic force applied by the electromagnetic coil 9 provided so as to go around the back surface of the mold 2. Therefore, the upward flow 5 in the direction of the molten metal surface 7 is also decelerated, and the fluctuation of the molten metal surface in the mold is suppressed.

FIG. 2 is a vertical sectional view of the upper part of the mold schematically showing the flow pattern in the mold at the time of low-speed casting of the present invention in comparison with the conventional method. FIG. 2 (a) shows the present invention to which an electromagnetic force is applied. FIG. 3B shows the case of the conventional method in which no electromagnetic force is applied. The same elements as those in FIG. 1 are denoted by the same reference numerals. When the casting speed decreases due to an operation trouble or the like, the amount of molten steel discharged from the SEN decreases.

As shown in FIG. 2B, in the conventional method in which no electromagnetic force is applied, the rising flow 5 decreases with the decrease in the molten steel discharge amount. Therefore, SEN near the molten metal surface 7
The upper layer flow 8 in one direction is reduced, and a dead zone 10 in which the flow of molten steel is extremely reduced near SEN1 is generated, and the surface of the molten metal is covered.

In the method of the present invention shown in FIG. 2 (a), an electromagnetic coil 9 is provided so as to go around the back of the mold.
An electromagnetic force is applied in the direction opposite to the case of the high-speed casting described with reference to FIG. As shown in the figure, the application of the electromagnetic force accelerates the discharge flow 4 from the SEN 1, promotes the upward flow 5, and increases the upper layer flow 8 in the SEN 1 direction near the molten metal surface 7.

Here, the reference value of the casting speed for changing the application direction of the electromagnetic force is, for example, the thickness of the slab × the width of 120,000.
If it is less than about ² mm ^2, it is about 2.5 to 3.0 m / min, 120
The value is set in a range of about 2.0 to 2.5 m / min for about 000 mm ² or more. However, the thickness and width of the slab are the dimensions of the outlet of the continuous casting machine, and the casting speed is the drawing speed.

That is, the slab cross-sectional area is 120,000 mm
In less than ² degrees, the reference value set in the range of about 2.5～3.0M / min, and in 120000Mm ² about or more,
The reference value is set in a range of about 2.0 to 2.5 m / min. When the casting speed is higher than the reference value, an electromagnetic force is applied so as to reduce the discharge flow from the SEN. When it was less than the above, an electromagnetic force was applied so as to accelerate the discharge flow.

[0022]

EXAMPLES (Example of the present invention) A medium-carbon aluminum killed steel having the components shown in Table 2 was cast using a vertical bending type continuous casting machine having the main specifications shown in Table 1. An electromagnetic coil was provided around the back of the mold, and a reference value of the casting speed was set at 2.5 m / min, and the application direction of the electromagnetic force was changed based on the reference value. That is, when the casting speed is equal to or higher than the reference value, S
Electromagnetic force was applied in the direction of decelerating the discharge flow from the EN (hereinafter, referred to as deceleration application), and when less than the reference value, electromagnetic force was applied in the direction of accelerating the discharge flow (hereinafter, referred to as acceleration application). The applied strength of the electromagnetic force was 4000 Gauss at the center of the mold.

[0023]

[Table 1]

[0024]

[Table 2]

Table 3 shows the casting conditions. As shown in the table, the casting speed was changed from 5 m / min to 1.5 m / min during the casting.

[0026]

[Table 3]

Fluctuations in the level of the molten metal during high-speed casting, the state of skinning of the molten metal in the mold during the low-speed casting, and the occurrence of vertical cracks in the slab were investigated.

(Comparative Example 1) Casting was performed under the same conditions as in the above-mentioned present invention except that the application of electromagnetic force, that is, the application of deceleration was stopped during casting at a casting speed of 5 m / min.

(Comparative Example 2) Casting was carried out under the same conditions as in the above-mentioned present invention example, except that the application of electromagnetic force, that is, the application of acceleration was stopped during casting at a casting speed of 1.5 m / min.

In the example of the present invention, at a casting speed of 5 m / min, the fluctuation of the molten metal level is as small as ± 3 mm or less.
At m / min, the flow between the mold and the SEN was good, and the state of powder slagging was not significantly different from that at a casting speed of 5 m / min, and stable casting was possible.

In Comparative Example 1, the variation in the level of the molten metal became extremely large at ± 20 mm or more at a casting speed of 5 m / min, and a breakout occurred about 4 minutes after the application of the electromagnetic force (deceleration application) was stopped. The subsequent casting was stopped.

In Comparative Example 2, application of electromagnetic force (application of acceleration)
After the stoppage, skinning of the surface of the water occurred between the mold and SEN,
The slag rim also grew significantly and became an unstable casting. Table 4 shows the occurrence of longitudinal cracks in the slabs of the present invention and Comparative Example 2.
It is shown by the vertical crack index (the ratio of the total vertical crack length to the slab length).

[0033]

[Table 4]

In the example of the present invention, the occurrence of vertical cracks is remarkably reduced, and it is judged that favorable slag formation of powder is realized by acceleration of the discharge flow under low-speed casting. On the other hand, in Comparative Example 2, it is considered that powder formation was poor and many vertical cracks occurred due to uneven inflow of powder.

Further, the present invention example and comparative example 2 during long-term operation
Table 4 also shows the incidence of breakout. As shown in the table, there is a large difference between the two in the breakout occurrence rate, and it has been found that stable casting can be performed even at low speed casting by applying appropriate molten steel flow to the meniscus part. did.

[0036]

According to the method of the present invention, in continuous casting of wide, thin and medium-thick cast pieces, stable casting can be performed even at low speed casting.

[Brief description of the drawings]

FIG. 1 is a vertical sectional view of an upper portion of a mold schematically showing a flow pattern in the mold during high-speed casting according to the present invention.

FIG. 2 is a vertical cross-sectional view of the upper part of the mold schematically showing the flow pattern in the mold at the time of low-speed casting of the present invention in comparison with the conventional method, and FIG. 2 (a) shows the case of the method of the present invention in which an electromagnetic force is applied. FIG. 3B shows the case of the conventional method in which no electromagnetic force is applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Immersion nozzle (SEN) 2 Mold 3 Short side 4 Discharge flow 5 Upflow 6 Downflow 7 Hot surface 8 Upper flow 9 Electromagnetic coil 10 Dead zone

Claims (1)

[Claims] In a continuous casting of wide and thin, medium and thick cast slabs,
Based on the reference value of the casting speed, casting is performed by changing the application direction of the electromagnetic force so as to reduce the discharge flow from the immersion nozzle if the reference value is equal to or more than the reference value, and to accelerate the discharge flow if the reference value is less than the reference value. A method for controlling the flow of a wide, thin and medium-thick cast slab in a mold.