JPWO2018198181A1 - Continuous steel casting method - Google Patents

Abstract

In a continuous casting method where an alternating magnetic field is applied to the in-mold molten steel to generate a swirling stirring flow in the in-mold molten steel, appropriate according to the immersion depth of the immersion nozzle and the distance from the in-mold molten steel surface to the peak position of the alternating magnetic field High flux density to produce high quality slabs. The continuous casting method of steel according to the present invention applies the alternating magnetic field to the molten steel in the mold through the alternating magnetic field generator installed opposite to the back of the pair of long sides of the mold and turns horizontally in the molten steel in the mold A continuous casting method of steel causing a stirring flow, wherein the distance between the mold long sides facing each other is 200 to 300 mm, and the discharge angle of the discharge hole of the immersion nozzle having two discharge holes is directed downward 5 ° A range of 50 °, a frequency of the AC magnetic field of 0.5 Hz to 3.0 Hz, and an AC magnetic field generated by the AC magnetic field generator and the immersion depth of the immersion nozzle according to the peak position of the AC magnetic field. The magnetic flux density at the peak position of is controlled to a predetermined range.

Description

  The present invention relates to a method for continuously casting steel, which applies an alternating magnetic field to molten steel in a mold and continuously casts the molten steel while controlling the flow of molten steel in the mold by the alternating magnetic field.

  In recent years, the quality requirements of high-grade steel plate products such as steel plates for automobiles, steel plates for cans, and high-performance thick steel plates are strict, and high quality is demanded at the stage of slab cast manufactured by continuous casting. . Oxide-based nonmetallic inclusions (hereinafter simply referred to as "inclusions") on the surface layer and inside of the slab as one of the qualities required for slab slabs (hereinafter also simply referred to as "slabs") There are few things.

  As inclusions trapped on the surface and inside of the slab, (1) Deoxidized product generated in the deoxidation process of molten steel with aluminum etc. and suspended in the molten steel, (2) Tundish and immersion nozzle There are bubbles of argon gas blown into the molten steel at (3) mold powder sprayed on the molten steel surface in the mold is caught in the molten steel and suspended. Since all of these result in surface defects and internal defects at the product stage, it is important to reduce inclusions trapped on the surface and inside of the slab.

  Conventionally, in order to prevent product defects due to inclusions, a magnetic field is applied to the molten steel in the mold to prevent deoxidation products in the molten steel, mold powder and argon bubbles from being trapped in the solidified shell, and Force is used to control the flow of molten steel. A number of proposals have been made for this technology.

  For example, in Patent Document 1, an alternating current magnetic field is applied to the discharge flow from the immersion nozzle immersed in in-mold molten steel, and the molten steel flow rate of the in-mold molten steel surface is equal to or higher than the inclusion deposition critical flow rate, and the mold powder is wound. A technique is disclosed that applies a braking force or a horizontal rotational force to the discharge flow so as to be in the range below the inflow critical flow rate.

  In Patent Document 2, the upper end of the AC magnetic field generation device is positioned 20 to 60 mm below the molten steel surface in the mold, and the immersion nozzle downwards 1 to 30 °, and the discharge flow from the immersion nozzle is of the AC magnetic field generation device. There is disclosed a method of continuously casting molten steel under control of impacting on a solidified shell ranging from the center to 450 mm below.

  Further, according to Patent Document 3, when the swirl magnetic flow in the mold width direction is applied to the molten steel in the mold by the AC magnetic field generator, the magnetic flux density at the discharge port of the immersion nozzle is 50% of the maximum magnetic flux density of the AC magnetic field generator. The method of installing the said discharge port in the position used as the following, and casting a molten steel continuously is disclosed.

JP 2003-320440 A Unexamined-Japanese-Patent No. 2000-202603 Japanese Patent Application Publication No. 2001-047201

  However, the above prior art has the following problems.

  That is, Patent Document 1 is a method of performing flow control by applying a braking force or a horizontal stirring force to the discharge flow from the immersion nozzle according to the value of the molten steel flow velocity in the in-mold molten steel surface, and therefore the mold Some equipment is required to measure or monitor the flow rate of molten steel at the surface of the internal molten steel. In addition, there is a concern that the accuracy of the critical flow velocity prediction formula may deteriorate when the installation position of the AC magnetic field generator installed on the mold rear surface is changed, and the AC magnetic field generator installed at any position on the mold rear surface It is difficult to say that the technology corresponds to

  Although patent document 2 is the technique which paid its attention to the position where the discharge flow from an immersion nozzle collides, it is limited when an alternating current magnetic field generator is installed near the molten metal melt surface in a mold, and an alternating current magnetic field generator is a mold It can not cope with the case where it is installed relatively lower than the inner molten steel surface.

  Similarly to Patent Document 2, Patent Document 3 is also limited to the case where the AC magnetic field generator is installed in the vicinity of the molten steel surface in the mold. In addition, although the discharge port of the immersion nozzle is installed at a position of 50% or less of the maximum magnetic flux density, in this case, since the discharge flow from the immersion nozzle is directed downward from the AC magnetic field generator, inclusions etc. There is a concern that it may sink below the AC magnetic field generator and cause internal defects in the slab.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to apply an alternating current magnetic field to an in-mold molten steel from an alternating-current magnetic field generator installed across a long side of the mold to stir and stir the in-mold molten steel. In the continuous casting method for generating flow, the appropriate alternating current magnetic flux density is given according to the distance from the mold molten steel surface to the peak position of the alternating current magnetic field and the immersion depth of the immersion nozzle, thereby making high quality slabs It is an object of the present invention to provide a method of continuous casting of steel that can be manufactured.

The gist of the present invention for solving the above-mentioned subject is as follows.
[1] A solidified shell formed by solidifying the molten steel while pouring the molten steel into a continuous casting mold having a pair of mold long sides and a pair of mold short sides and forming a rectangular internal space A continuous casting method of steel which is drawn out from steel to produce a slab,
An alternating current magnetic field is applied to the molten steel in the mold via an alternating magnetic field generator disposed oppositely across the long side of the mold on the back of the pair of long sides of the mold, and the molten steel in the mold is horizontal by the alternating magnetic field To create a swirling flow in the direction of
The distance between the opposing mold long sides is 200 to 300 mm,
The discharge angle of the discharge hole of the immersion nozzle having two discharge holes for injecting the molten steel into the internal space is in the range of 5 ° downward to 50 ° downward,
The frequency of the alternating magnetic field is set to 0.5 Hz or more and 3.0 Hz or less,
The distance from the mold molten steel surface to the peak position of the AC magnetic field is 200 mm or more and less than 300 mm,
The immersion depth of the immersion nozzle (the distance from the in-mold molten steel surface to the upper end of the discharge hole of the immersion nozzle) is 100 mm or more and less than 200 mm,
The continuous casting method of steel which makes the magnetic flux density of the peak position of the said alternating current magnetic field 0.040T or more and less than 0.060T.
[2] A molten steel is poured into a continuous casting mold having a pair of mold long sides and a pair of mold short sides and forming a rectangular internal space, and a solidified shell formed by solidifying the molten steel is used as the mold A continuous casting method of steel which is drawn out from steel to produce a slab,
An alternating current magnetic field is applied to the molten steel in the mold via an alternating magnetic field generator disposed oppositely across the long side of the mold on the back of the pair of long sides of the mold, and the molten steel in the mold is horizontal by the alternating magnetic field To create a swirling flow in the direction of
The distance between the opposing mold long sides is 200 to 300 mm,
The discharge angle of the discharge hole of the immersion nozzle having two discharge holes for injecting the molten steel into the internal space is in the range of 5 ° downward to 50 ° downward,
The frequency of the alternating magnetic field is set to 0.5 Hz or more and 3.0 Hz or less,
The distance from the in-mold molten steel surface to the peak position of the AC magnetic field is 300 mm or more and less than 400 mm,
The immersion depth of the immersion nozzle (the distance from the in-mold molten steel surface to the upper end of the discharge hole of the immersion nozzle) is 100 mm or more and less than 300 mm,
The continuous casting method of steel which makes the magnetic flux density of the peak position of the said alternating current magnetic field more than 0.060T and less than 0.080T.
[3] A solidified shell formed by solidifying the molten steel while pouring the molten steel into a continuous casting mold having a pair of mold long sides and a pair of mold short sides and forming a rectangular internal space is the mold A continuous casting method of steel which is drawn out from steel to produce a slab,
An alternating current magnetic field is applied to the molten steel in the mold via an alternating magnetic field generator disposed oppositely across the long side of the mold on the back of the pair of long sides of the mold, and the molten steel in the mold is horizontal by the alternating magnetic field To create a swirling flow in the direction of
The distance between the opposing mold long sides is 200 to 300 mm,
The discharge angle of the discharge hole of the immersion nozzle having two discharge holes for injecting the molten steel into the internal space is in the range of 5 ° downward to 50 ° downward,
The frequency of the alternating magnetic field is set to 0.5 Hz or more and 3.0 Hz or less,
The distance from the in-mold molten steel surface to the peak position of the AC magnetic field is 400 mm or more and less than 500 mm,
The immersion depth of the immersion nozzle (the distance from the in-mold molten steel surface to the upper end of the discharge hole of the immersion nozzle) is 100 mm or more and less than 300 mm,
The continuous casting method of steel which makes the magnetic flux density of the peak position of the said alternating current magnetic field 0.080T or more and less than 0.100T.
[4] A solidified shell formed by solidifying the molten steel while pouring the molten steel into a continuous casting mold having a pair of mold long sides and a pair of mold short sides and forming a rectangular internal space is the mold A continuous casting method of steel which is drawn out from steel to produce a slab,
An alternating current magnetic field is applied to the molten steel in the mold via an alternating magnetic field generator disposed oppositely across the long side of the mold on the back of the pair of long sides of the mold, and the molten steel in the mold is horizontal by the alternating magnetic field To create a swirling flow in the direction of
The distance between the opposing mold long sides is 200 to 300 mm,
The discharge angle of the discharge hole of the immersion nozzle having two discharge holes for injecting the molten steel into the internal space is in the range of 5 ° downward to 50 ° downward,
The frequency of the alternating magnetic field is set to 0.5 Hz or more and 3.0 Hz or less,
Depending on the peak position of the AC magnetic field, the immersion depth of the immersion nozzle (the distance from the molten metal in the mold to the upper end of the discharge hole of the immersion nozzle) and the magnetic flux density of the AC magnetic field peak position by the AC magnetic field generator A continuous casting method of steel, wherein any one of the following three conditions (A), (B) and (C) is satisfied.
Condition (A); When the distance from the mold molten steel surface to the peak position of the alternating current magnetic field is 200 mm or more and less than 300 mm, the immersion depth of the immersion nozzle is 100 mm or more and less than 200 mm. The magnetic flux density is set to 0.040 T or more and less than 0.060 T.
Condition (B): When the distance from the in-mold molten steel surface to the peak position of the alternating current magnetic field is 300 mm or more and less than 400 mm, the immersion depth of the immersion nozzle is 100 mm or more and less than 300 mm. The magnetic flux density is set to not less than 0.060 T and less than 0.080 T.
Condition (C): When the distance from the mold molten steel surface to the peak position of the AC magnetic field is 400 mm or more and less than 500 mm, the immersion depth of the immersion nozzle is 100 mm or more and less than 300 mm, and the peak position of the AC magnetic field The magnetic flux density is set to at least 0.080 T and less than 0.100 T.

  According to the present invention, an alternating magnetic field of an appropriate magnetic flux density according to the distance from the in-mold molten steel surface to the peak position of the alternating magnetic field and the immersion depth of the immersion nozzle is applied to give a swirling stirring flow to the in-mold molten steel. Therefore, deoxidation products, argon gas bubbles and entrapment of mold powder in a solidified shell are suppressed, and it is realized that a high-quality cast piece is easily produced.

FIG. 1 is a view showing an example of an embodiment of the present invention, and is a schematic view of a mold portion of a slab continuous casting machine. FIG. 2 is an enlarged view of the immersion nozzle shown in FIG.

  Hereinafter, embodiments of the present invention will be described.

  The present inventors apply an alternating magnetic field to the molten steel in the mold and cause horizontal swirling flow in the molten steel in the mold by the alternating magnetic field, and the flow condition of molten steel in the mold in the continuous casting method of steel is low. Tests and investigations were performed using a melting point alloy device. In the test, using a mold having a pair of mold long sides and a pair of mold short sides and forming a rectangular internal space, an immersion nozzle having two discharge holes at the center of the internal space (hereinafter referred to as “2 (Also described as “hole type immersion nozzle”) to simulate the discharge flow of molten steel from the respective discharge holes toward the short side of the mold, in particular, the peak position of the AC magnetic field and the immersion depth of the immersion nozzle It tested about the molten steel flow condition in the mold at the time of changing.

  Here, the peak position of the AC magnetic field means the maximum root mean square value per time cycle of the component orthogonal to the inner wall surface of the magnetic flux density of the AC magnetic field on the inner wall surface of the mold surrounding the inner space of the mold. This position is the largest along the wall. Further, the immersion depth of the immersion nozzle is defined by the distance from the in-mold molten steel surface (also referred to as "meniscus") to the upper end of the discharge hole of the immersion nozzle.

  In the test, the installation position of the AC magnetic field generator installed opposite to the back of the long side of the mold and the installation position of the immersion nozzle, that is, the immersion depth is changed, and the flow condition of the low melting point alloy in the mold and the inside of the mold at that time. The flow velocity distribution etc. were investigated using numerical calculation and a low melting point alloy device of real machine 1/4 size. As a low melting point alloy, a Bi-Pb-Sn-Cd alloy (melting point: 70 ° C.) was used.

  As a result of investigation, it has been found that an appropriate application range of the magnetic flux density of the alternating magnetic field exists depending on the peak position of the alternating magnetic field and the immersion depth of the immersion nozzle. That is, it turned out that the application condition of an alternating current magnetic field can be divided roughly into three types of conditions (A)-(C) by the peak position of alternating current magnetic field, and the immersion depth of an immersion nozzle. The survey results are shown in Table 1. The peak position of the alternating magnetic field is defined by the distance from the molten metal in the mold to the peak position of the alternating magnetic field.

1; Condition (A)
When the peak position of the AC magnetic field is 200 mm or more and less than 300 mm from the in-mold molten steel surface, the magnetic flux density at the peak position of the AC magnetic field is 0 when the immersion depth of the two-hole immersion nozzle is 100 mm or more and less than 200 mm. .040 T or more and less than 0.060 T

  The magnetic flux density is a direction from the plane forming the inner space of the mold copper plate to the back of the mold copper plate on which the AC magnetic field generator is disposed, and the direction toward the inner space along the normal direction of the plane. Among the magnetic flux density in the normal direction at a position 15 mm away from the plane, the effective value (root mean square value; Root Mean Square) of the magnetic flux density at the peak position of the magnetic flux density along the slab drawing direction , It is defined by an arithmetic mean value of values measured at an arbitrary pitch in the mold width direction. The measurement pitch in the mold width direction is considered to be sufficient if it can sufficiently represent the representativeness of the space profile of the magnetic flux density.

  If the magnetic flux density is less than 0.040 T, it is difficult to exert a cleaning effect from the solidified shells of argon gas bubbles and deoxidized products because the swirling stirring force is weak. On the other hand, in the case where the magnetic flux density is 0.060 T or more, the swirling stirring force is too strong, which promotes the winding of the mold powder.

  When the immersion depth of the immersion nozzle is less than 100 mm, the distance between the in-mold molten steel surface and the discharge flow is too short, so that the fluctuation of the surface is likely to be promoted in the mold. When the immersion depth is 200 mm or more, the immersion nozzle main body becomes longer, the refractory cost increases, and the immersion nozzle tends to be damaged from the viewpoint of heat resistance and load resistance, which in turn causes the operation cost There is concern that the

2; Condition (B)
When the peak position of the AC magnetic field is 300 mm or more and less than 400 mm from the in-mold molten steel surface, the magnetic flux density at the peak position of the AC magnetic field is 0 when the immersion depth of the 2-hole immersion nozzle is 100 mm or more and less than 300 mm. .060 T or more and less than 0.080 T

  Since the peak position of the AC magnetic field is deeper from the molten steel surface in the mold compared to the condition (A), a magnetic flux density stronger than the condition (A) is required. That is, when the magnetic flux density is less than 0.060 T, it is difficult to exert the cleaning effect of the argon gas bubbles and the deoxidized product from the solidified shell because the swirling stirring force is weak. On the other hand, when the magnetic flux density is equal to or greater than 0.080 T, the swirling stirring force is too strong, which promotes the winding of the mold powder.

  When the immersion depth of the immersion nozzle is less than 100 mm, the distance between the in-mold molten steel surface and the discharge flow is too short, so that the fluctuation of the surface is likely to be promoted in the mold. If the immersion depth is 300 mm or more, the immersion nozzle main body becomes longer, the refractory cost is increased, and the immersion nozzle is easily damaged from the viewpoints of heat resistance and load resistance, and the operation cost is reduced. There is concern that the

3; Condition (C)
When the peak position of the AC magnetic field is 400 mm or more and less than 500 mm from the in-mold molten steel surface, the magnetic flux density at the peak position of the AC magnetic field is 0 when the immersion depth of the two-hole immersion nozzle is 100 mm or more and less than 300 mm. Not less than .080T and less than 0.100T.

  Since the peak position of the AC magnetic field is deeper from the in-mold molten steel surface than in the conditions (A) and (B), a stronger magnetic flux density is required. That is, when the magnetic flux density is less than 0.080 T, it is difficult to exert a cleaning effect on the solidified shell of argon gas bubbles and deoxidized products because the swirling stirring force is weak. On the other hand, when the magnetic flux density is 0.100 T or more, the swirling stirring force is too strong, thereby promoting mold powder entrainment.

  When the immersion depth of the immersion nozzle is less than 100 mm, the distance between the in-mold molten steel surface and the discharge flow is too short, so that the fluctuation of the surface is likely to be promoted in the mold. If the immersion depth is 300 mm or more, the immersion nozzle main body becomes longer, the refractory cost is increased, and the immersion nozzle is easily damaged from the viewpoints of heat resistance and load resistance, and the operation cost is reduced. There is concern that the

  In the conditions (A) to (C), the discharge angle of the immersion nozzle used is in the range of 5 ° downward to 50 ° downward. When the discharge angle is smaller than 5 ° downward, the alternating magnetic field can not sufficiently act on the discharge flow. On the other hand, if the discharge angle is larger than 50 ° downward, the downward flow of the discharge flow becomes too strong, so the deoxidized product or gas bubbles sink into a deep position in the casting direction and become an internal defect, resulting in the steel plate There is a concern that it becomes a starting point of cracking during molding processing.

  In the present invention, the peak position of the AC magnetic field is 200 mm or more and less than 500 mm from the in-mold molten steel surface. When the peak position of the alternating magnetic field is less than 200 mm from the in-mold molten steel surface, in order to apply the alternating magnetic field to the discharge flow from the immersion nozzle, the immersion depth of the immersion nozzle is shallower than the alternating magnetic field peak position This imposes operational constraints and prevents efficient application of alternating magnetic fields. In addition, when the peak position of the AC magnetic field is at a position 500 mm or more away from the in-mold molten steel surface, the swirling stirring flow is applied in the area where the solidified shell has grown, and deoxidation products and argon gas bubbles The cleaning effect on the coagulated shell is poor.

  The frequency of the alternating magnetic field is 0.5 to 3.0 Hz, preferably 1.0 to 2.0 Hz. If the frequency is less than 0.5 Hz, the application of electromagnetic force by the alternating magnetic field becomes too intermittent, and the cleaning effect of the deoxidation product or the argon gas bubble on the solidified shell is not stable. On the other hand, when the frequency exceeds 3.0 Hz, the attenuation of the magnetic flux density by the mold and the solidified shell becomes large, and the alternating magnetic field can not be applied efficiently to the molten steel in the mold.

  Hereinafter, a specific implementation method of the present invention will be described based on the drawings. FIG. 1 is a view showing an example of an embodiment of the present invention, and is a schematic view of a mold portion of a slab continuous caster, and FIG. 2 is an enlarged view of an immersion nozzle shown in FIG.

  In FIG. 1 and FIG. 2, 1 is a molten steel, 2 is a solidified shell, 3 is a molten steel surface in a mold, 4 is a discharge flow, 5 is a cast slab, 6 is a mold, 7 is a water-cooled mold long side, 8 is a A water-cooled mold short side, 9 is an immersion nozzle, 10 is a discharge hole, 11 is an AC magnetic field generator, 12 is a mold powder, and θ is a discharge angle of the immersion nozzle.

  The mold 6 has a pair of opposing mold long sides 7 and a pair of opposing mold short sides 8 sandwiched by the mold long sides 7, and the pair of mold long sides 7 and the pair of mold short sides 8 And a rectangular internal space is formed. A pair of alternating current magnetic field generating devices 11 disposed opposite to each other across the long side 7 of the mold are installed on the back of the long side 7 of the mold. Here, the distance between mutually opposing mold long sides is 200 to 300 mm, the immersion nozzle 9 has two discharge holes 10, and the discharge angle (θ) of the discharge holes 10 is in the range of 5 ° downward to 50 ° downward It is.

The immersion nozzle 9 is placed at the center of the rectangular internal space of the mold 6, and the discharge flow 4 of the molten steel 1 is discharged from the two discharge holes 10 toward the mold short side 8 where the discharge holes 10 face each other. The molten steel 1 is injected into the inner space of the mold 6. The molten steel 1 injected into the inner space of the mold 6 is cooled by the mold long side 7 and the mold short side 8 to form a solidified shell 2. Then, when a predetermined amount of molten steel 1 is injected into the inner space of the mold 6, a pinch roll (not shown) is driven to solidify the outer shell in a state where the discharge holes 10 are immersed in the molten steel 1 in the mold. Pulling out of the cast slab 5 having the unsolidified molten steel 1 inside as the shell 2 is started. After the start of drawing, while controlling the position of the molten steel melt surface 3 in the mold to a substantially constant position, the cast strip drawing speed is increased to a predetermined cast strip drawing speed. In FIG. 1, the immersion depth of the immersion nozzle 9 is indicated by "L ₁ ", and the distance from the in-mold molten steel surface 3 to the peak position of the alternating magnetic field is indicated by "L ₂ ".

  Mold powder 12 is added onto the molten steel surface 3 in the mold. The mold powder 12 melts, prevents oxidation of the molten steel 1 and flows between the solidified shell 2 and the mold 6 to exert an effect as a lubricant. In addition, in the molten steel 1 flowing down the immersion nozzle 9, argon gas, nitrogen gas or a mixture of argon gas and nitrogen gas is used to prevent adhesion of the deoxidized product suspended in the molten steel to the inner wall of the immersion nozzle. Blow in the gas.

  Thus, when continuously casting the molten steel 1, an alternating current magnetic field is applied from the alternating current magnetic field generator 11 to the molten steel 1 in the mold to generate a horizontal swirling flow in the molten steel 1 in the mold. The frequency of the alternating magnetic field is 0.5 Hz or more and 3.0 Hz or less.

When applying an alternating magnetic field, the immersion depth of the immersion nozzle 9 in the case where the distance (L ₂ ) from the in-mold molten steel surface 3 to the peak position of the alternating magnetic field is 200 mm or more and less than 300 mm (condition (A)). (L ₁ ) is 100 mm or more and less than 200 mm, and the magnetic flux density at the peak position of the alternating magnetic field is 0.040 T or more and less than 0.060 T.

In addition, when the distance (L ₂ ) from the mold molten steel surface 3 to the peak position of the alternating current magnetic field is 300 mm or more and less than 400 mm (condition (B)), the immersion depth (L ₁ ) of the immersion nozzle 9 is 100 mm. The magnetic flux density at the peak position of the alternating magnetic field is set to 0.060 T or more and less than 0.080 T.

Furthermore, when the distance (L ₂ ) from the mold molten steel surface 3 to the peak position of the AC magnetic field is 400 mm or more and less than 500 mm (condition (C)), the immersion depth (L ₁ ) of the immersion nozzle 9 is 100 mm or more and less than 300 mm, and the magnetic flux density at the peak position of the AC magnetic field is 0.080 T or more and less than 0.100 T.

  Adjustment of the magnetic flux density at the peak position of the alternating magnetic field is performed as follows. That is, the relationship between the power supplied to the AC magnetic field generator 11 and the magnetic flux density at a position 15 mm away from the surface of the mold copper plate at the peak position of the AC magnetic field in the internal space of the mold 6 is measured beforehand. The power supplied to the alternating current magnetic field generator 11 is adjusted so that the magnetic flux density at the peak position of the magnetic flux density becomes the desired magnetic flux density.

As described above, according to the present invention, the magnetic flux density appropriate for the distance (L ₂ ) from the in-mold molten steel surface 3 to the peak position of the AC magnetic field and the immersion depth (L ₁ ) of the immersion nozzle Since an alternating magnetic field is applied to give a swirling stirring flow to the molten steel in the mold, deoxidation products, argon gas bubbles, and capture of mold powder 12 to the solidified shell 2 are suppressed, and high quality slab slabs are easily manufactured. To be realized.

Using a slab continuous caster having a mold as shown in FIG. 1, variously change the immersion depth (L ₁ ) of the immersion nozzle and the distance (L ₂ ) from the in-mold molten steel surface to the peak position of the AC magnetic field A test was conducted to continuously cast about 300 tons of aluminum killed molten steel. The slab slab has a thickness of 250 mm and a width of 1000 to 2200 mm, and the molten steel injection flow rate in the steady casting area is 2.0 to 6.5 ton / min (1.0 to 3.0 m / min in slab extraction speed) And Moreover, the frequency of the alternating magnetic field was 1.0 Hz.

  The immersion nozzle used was a two-hole immersion nozzle with a discharge angle (θ) directed downward of 25 °, and argon gas was blown into the molten steel flowing down the immersion nozzle through the upper nozzle. The hot-rolled, cold-rolled, and alloyed hot-dip galvanizing treatments were sequentially applied to the cast slab slabs. The surface defects in this alloyed galvanized steel sheet were continuously measured by an on-line surface defect measuring apparatus. Perform an overview observation of the measured defects, SEM analysis and ICP analysis, and among the measured defects, identify steelmaking defects (deoxidizing physical property defects, argon gas foaming defects, mold powder properties defects) and perform alloying and melting The number of steelmaking defects per 100 m in length of the galvanized steel sheet (product defect index) was evaluated.

  The test results corresponding to the inventive examples are shown in Table 2, and the test results corresponding to the Comparative Example are shown in Table 3.

  Invention Examples 1 to 12 correspond to the condition (A) in Table 1, Invention Examples 13 to 24 correspond to the condition (B) in Table 1, and Invention Examples 25 to 36 are the conditions in Table 1 It corresponds to (C). In all of Invention Examples 1 to 36, the product defect index was in the range of 0.21 to 0.34 pieces / 100 m, which was a good result.

  On the other hand, in Comparative Examples 1 to 24, the magnetic flux density at the peak position of the alternating magnetic field was a test outside the scope of the present invention, and the product defect index was inferior at 0.46 to 0.55 pieces / 100 m.

Moreover, Comparative Examples 25 to 32 are tests in which the immersion depth (L ₁ ) of the immersion nozzle is out of the range of the present invention, and the product defect index is also inferior such as 0.47 to 0.55 pieces / 100 m. The In Comparative Examples 25 to 32, the distance (L ₂ ) from the in-mold molten steel surface to the peak position of the alternating current magnetic field is only the case corresponding to the condition (A) in Table 1, but the condition (B) and the condition (C) Also in the case of), it has been confirmed that the product defect index is deteriorated when the immersion depth (L ₁ ) of the immersion nozzle is out of the range of the present invention.

  In addition, although not described in the present example, it is confirmed that the same effect as that described in the present example can be obtained when the thickness of the slab is in the range of 200 to 300 mm. Further, the shape of the immersion nozzle is not limited to the conditions described in the present embodiment, and the same effect can be obtained if the discharge angle (θ) is in the range of 5 ° downward to 50 ° downward. Have confirmed.

  Thus, it has been confirmed that by applying the continuous casting method according to the present invention, slab slabs of excellent quality can be cast.

DESCRIPTION OF SYMBOLS 1 Molten steel 2 Solidification shell 3 Molten steel surface in mold 4 Discharge flow 5 Slab 6 Mold 7 Mold long side 8 Mold short side 9 Immersion nozzle 10 Discharge hole 11 AC magnetic field generator 12 Mold powder

Claims (4)

While pouring molten steel into a continuous casting mold having a pair of mold long sides and a pair of mold short sides and forming a rectangular internal space, a solidified shell formed by solidifying the molten steel is drawn from the mold A continuous casting method of steel for producing a slab,
An alternating current magnetic field is applied to the molten steel in the mold via an alternating magnetic field generator disposed oppositely across the long side of the mold on the back of the pair of long sides of the mold, and the molten steel in the mold is horizontal by the alternating magnetic field To create a swirling flow in the direction of
The distance between the opposing mold long sides is 200 to 300 mm,
The discharge angle of the discharge hole of the immersion nozzle having two discharge holes for injecting the molten steel into the internal space is in the range of 5 ° downward to 50 ° downward,
The frequency of the alternating magnetic field is set to 0.5 Hz or more and 3.0 Hz or less,
The distance from the mold molten steel surface to the peak position of the AC magnetic field is 200 mm or more and less than 300 mm,
The immersion depth of the immersion nozzle (the distance from the in-mold molten steel surface to the upper end of the discharge hole of the immersion nozzle) is 100 mm or more and less than 200 mm,
The continuous casting method of steel which makes the magnetic flux density of the peak position of the said alternating current magnetic field 0.040T or more and less than 0.060T. While pouring molten steel into a continuous casting mold having a pair of mold long sides and a pair of mold short sides and forming a rectangular internal space, a solidified shell formed by solidifying the molten steel is drawn from the mold A continuous casting method of steel for producing a slab,
An alternating current magnetic field is applied to the molten steel in the mold via an alternating magnetic field generator disposed oppositely across the long side of the mold on the back of the pair of long sides of the mold, and the molten steel in the mold is horizontal by the alternating magnetic field To create a swirling flow in the direction of
The distance between the opposing mold long sides is 200 to 300 mm,
The discharge angle of the discharge hole of the immersion nozzle having two discharge holes for injecting the molten steel into the internal space is in the range of 5 ° downward to 50 ° downward,
The frequency of the alternating magnetic field is set to 0.5 Hz or more and 3.0 Hz or less,
The distance from the in-mold molten steel surface to the peak position of the AC magnetic field is 300 mm or more and less than 400 mm,
The immersion depth of the immersion nozzle (the distance from the in-mold molten steel surface to the upper end of the discharge hole of the immersion nozzle) is 100 mm or more and less than 300 mm,
The continuous casting method of steel which makes the magnetic flux density of the peak position of the said alternating current magnetic field more than 0.060T and less than 0.080T. While pouring molten steel into a continuous casting mold having a pair of mold long sides and a pair of mold short sides and forming a rectangular internal space, a solidified shell formed by solidifying the molten steel is drawn from the mold A continuous casting method of steel for producing a slab,
An alternating current magnetic field is applied to the molten steel in the mold via an alternating magnetic field generator disposed oppositely across the long side of the mold on the back of the pair of long sides of the mold, and the molten steel in the mold is horizontal by the alternating magnetic field To create a swirling flow in the direction of
The distance between the opposing mold long sides is 200 to 300 mm,
The discharge angle of the discharge hole of the immersion nozzle having two discharge holes for injecting the molten steel into the internal space is in the range of 5 ° downward to 50 ° downward,
The frequency of the alternating magnetic field is set to 0.5 Hz or more and 3.0 Hz or less,
The distance from the in-mold molten steel surface to the peak position of the AC magnetic field is 400 mm or more and less than 500 mm,
The immersion depth of the immersion nozzle (the distance from the in-mold molten steel surface to the upper end of the discharge hole of the immersion nozzle) is 100 mm or more and less than 300 mm,
The continuous casting method of steel which makes the magnetic flux density of the peak position of the said alternating current magnetic field 0.080T or more and less than 0.100T. While pouring molten steel into a continuous casting mold having a pair of mold long sides and a pair of mold short sides and forming a rectangular internal space, a solidified shell formed by solidifying the molten steel is drawn from the mold A continuous casting method of steel for producing a slab,
An alternating current magnetic field is applied to the molten steel in the mold via an alternating magnetic field generator disposed oppositely across the long side of the mold on the back of the pair of long sides of the mold, and the molten steel in the mold is horizontal by the alternating magnetic field To create a swirling flow in the direction of
The distance between the opposing mold long sides is 200 to 300 mm,
The discharge angle of the discharge hole of the immersion nozzle having two discharge holes for injecting the molten steel into the internal space is in the range of 5 ° downward to 50 ° downward,
The frequency of the alternating magnetic field is set to 0.5 Hz or more and 3.0 Hz or less,
Depending on the peak position of the AC magnetic field, the immersion depth of the immersion nozzle (the distance from the molten metal in the mold to the upper end of the discharge hole of the immersion nozzle) and the magnetic flux density of the AC magnetic field peak position by the AC magnetic field generator A continuous casting method of steel, wherein any one of the following three conditions (A), (B) and (C) is satisfied.
Condition (A); When the distance from the mold molten steel surface to the peak position of the alternating current magnetic field is 200 mm or more and less than 300 mm, the immersion depth of the immersion nozzle is 100 mm or more and less than 200 mm. The magnetic flux density is set to 0.040 T or more and less than 0.060 T.
Condition (B): When the distance from the in-mold molten steel surface to the peak position of the alternating current magnetic field is 300 mm or more and less than 400 mm, the immersion depth of the immersion nozzle is 100 mm or more and less than 300 mm. The magnetic flux density is set to not less than 0.060 T and less than 0.080 T.
Condition (C): When the distance from the mold molten steel surface to the peak position of the AC magnetic field is 400 mm or more and less than 500 mm, the immersion depth of the immersion nozzle is 100 mm or more and less than 300 mm, and the peak position of the AC magnetic field The magnetic flux density is set to at least 0.080 T and less than 0.100 T.

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