JP2010110797A - Continuous casting method of slab which has static magnetic field act on upward flow over narrow surface in mold - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology which avoids remarkable delay in solidification which is a cause of a breakout just below a mold, and powder entrainment which causes sliver defects. <P>SOLUTION: Magnetic flux density is measured at the center of the mold thickness direction on a narrow surface 1a in a mold. A magnetic field of which the vertical component B [T] for the narrow surface 1a in the mold is 0.05 or more is formed from an application commencing position M1 [mm] where a meniscus distance M [mm] is 100 to 300 to an application terminating position M2 [mm] where the meniscus distance M [mm] is 300 to 500 and in addition, so that the distance ΔM3 [mm] from the application commencing position M1 [mm] to the application terminating position M2 [mm] is 150 to 400. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a slab continuous casting method in which a static magnetic field is applied to an upward flow of a mold narrow surface.

  For example, Patent Document 1 (Patent No. 34178871), Patent Document 2 (Patent No. 34178861), Patent Document 3 (Patent No. 3372863), and Patent Document 4 (Patent No. 2610741) were discharged from the immersion nozzle. It is described that a molten steel flow collides with a mold narrow surface and branches, and a static magnetic field is applied to a so-called downward flow that goes downward, and thus a braking force is applied to the downward flow. In particular, Patent Documents 1 to 3 indicate that, in the vicinity of the mold short surface, even if a magnetic field is applied in the mold thickness direction, a current is hardly induced in the mold width direction. In this case, the magnetic force in the long side direction of the mold is generated in the molten steel (see FIG. 5 of Patent Document 1).

  In addition, in Patent Document 5 (Patent No. 3056659), when performing casting while pinching the molten steel metal in the mold by electromagnetic force, the electromagnetic force concentrates on the mold corner portion, leading to abnormal flow of the molten metal surface. In order to suppress this abnormal flow, it is described that a permanent magnet is installed at the corner portion and an electromagnetic brake effect is applied only to the corner portion (see Patent Document 5, 0006, 0008, 0013, 0014, etc.). FIG. 4 of Patent Document 5 discloses a one-hole type immersion nozzle.

  However, in any of the documents, the so-called ascending flow that goes upward due to the molten steel flow discharged from the immersion nozzle colliding with the mold narrow surface is hardly mentioned. In particular, since the technique disclosed in Patent Document 5 employs a one-hole immersion nozzle, the above-described upward flow cannot be touched.

  On the other hand, the inventors of the present application have paid attention to the fact that the direct mold-type breakout and product sliver defects, which are serious problems in operation, are closely related to the above-mentioned upward flow after intensive studies. The present invention has been made in view of these points, and a main object thereof is to provide a technique for avoiding a mold-type breakout / product sliver defect caused by an upward flow of molten steel in the mold. .

Means and effects for solving the problems

  The problems to be solved by the present invention are as described above. Next, means for solving the problems and the effects thereof will be described.

  According to an aspect of the present invention, a mold having a mold width W [mm] of 1200 to 2100 is used and a pair of opposed molten steel discharge holes is formed, and a molten steel discharge flow from the molten steel discharge holes is provided. Downward angle θ [deg. ] Is set to 15 to 45 on the basis of the horizontal, the virtual intersection of the lower end line of the molten steel discharge hole specified by the vertical section of the immersion nozzle and the axis of the immersion nozzle is from the meniscus. The continuous casting of the slab, which is immersed in the molten steel so as to be 150 to 350 [mm] below and the casting speed Vc [m / min] is 1.4 to 2.8, is performed by the following method. . When the magnetic flux density is measured at the center of the mold thickness direction on the narrow mold surface, a magnetic field having a perpendicular component B [T] of 0.05 or more with respect to the narrow mold surface is set to a meniscus distance M [mm] of 100 to 300. From the application start position M1 [mm] as the position to be applied to the application end position M2 [mm] as the position where the meniscus distance M [mm] is 300 to 500, in addition, from the application start position M1 [mm] It forms so that distance (DELTA) M3 [mm] to application completion position M2 [mm] may be set to 150-400, respectively.

  According to the above method, since the magnetic field has a component perpendicular to the mold narrow surface, the molten steel flow discharged from the submerged nozzle collides with the mold narrow surface and branches to a so-called upward flow upward. On the other hand, the braking force acts efficiently. Moreover, since this braking force acts largely in proportion to the flow velocity of the upward flow, there is also an effect of suppressing the drift of the molten steel discharge flow. Further, since the braking force acts on the upward flow and the drift is suppressed, it is possible to avoid a significant solidification delay that is a cause of the mold-type breakout and a powder entrainment that is a cause of a product sliver defect. Therefore, a high casting speed can be realized, thereby contributing to high productivity.

  Although the story goes back, the above-mentioned Patent Document 5 is largely different from the present invention in that the molten steel discharge flow discharged from the immersion nozzle is completely different from that of the present invention, and is further superimposed on the moving magnetic field for pinching. Since the main point is placed where a static magnetic field is applied, the viewpoint is completely different from the inventors of the present application.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic view of a continuous casting machine. First, based on this figure, the structure and operation | movement of the continuous casting machine 100 are demonstrated easily as an example.

  The continuous casting machine 100 smoothly pours molten metal held in a tundish (not shown) into the mold 1 at a predetermined flow rate for cooling the molten steel to form a shell having a predetermined shape. And a plurality of roll pairs 3 arranged in parallel along the casting path Q from directly below the mold 1. The immersion nozzle 2 is a general two-hole type that discharges molten steel obliquely downward toward each mold narrow surface. The structure of the immersion nozzle 2 will be described in detail later with reference to FIGS. In the present embodiment, the casting path Q is provided with a vertical path portion extending in a substantially vertical direction, an arc path portion connected to the vertical path portion and extending in an arc shape, and further provided on the downstream side thereof and extending in the horizontal direction. It consists of a horizontal path | route part and the correction | amendment path | route part for connecting the said circular arc path | route part and a horizontal path | route part smoothly. That is, the continuous casting machine 100 according to the present embodiment is configured as a vertical sequential bending die. It may be a curved type in which the vertical path portion is omitted.

  Each of the roll pairs 3 is composed of a pair of rolls 3a and 3a for sandwiching a slab as a casting object with both wide surfaces. The roll gap [mm] as the shortest distance between the roll surfaces of the pair of rolls 3a and 3a is configured to be adjustable by appropriate means.

  Further, upstream of the casting path Q, a cooling spray 4 is appropriately provided for spraying cooling water at a predetermined flow rate on the shell formed in the mold 1 and pulled out from the mold 1. In general, the mold 1 is referred to as a primary cooling zone, and in this sense, a path portion where the cooling spray 4 is disposed is referred to as a secondary cooling zone.

  The shell pulled out from the mold 1 and transported along the casting path Q is further cooled and contracted by natural heat radiation, the cooling spray 4 or the like. Therefore, the roll gap [mm] of the roll pair 3 is generally set so as to be gradually narrowed as it proceeds to the downstream side of the casting path Q.

  In order to start continuous casting of the slab slab with the above configuration, a dummy bar (not shown) is inserted into the casting path Q in advance before pouring molten steel into the mold 1, Then, the molten steel starts to be poured into the mold 1 and the dummy bar is pulled out downstream. The amount of molten steel poured into the mold 1 and the pulling speed of the dummy bar are gradually increased until the casting speed reaches a predetermined casting speed. The dummy bar is collected by an appropriate means when a predetermined meniscus distance is reached. Thus, the slab slab is continuously cast.

Next, general operating conditions of the continuous casting machine 100 will be briefly introduced. The following is an example.
-Mold width W [mm] shall be 800-2100.
-Mold thickness D [mm] shall be 230-280.
-Mold height H [mm] shall be 800-900.
-Casting speed Vc [m / min] shall be 1.0-3.0.
-Molten steel superheat degree (DELTA) T [degreeC] shall be 0-40.
The specific water amount Wt [L / kg Steel] is 1 to 3.
-In-mold electromagnetic stirring intensity M-EMS [gauss] shall be 0-1000.
-Molten steel composition is based on an agreement between the parties. Typical components are C, Si, and Mn. To this, Cr, Cu or the like is appropriately added. Contains other inevitable impurities.

Here, each term is briefly explained.
The mold width W [mm] and the mold thickness D [mm] are specified at the upper end of the mold 1 (see also FIG. 3).
The casting speed Vc [m / min] is a drawing speed of the slab, and is specified by the peripheral speed of the roll pair 3 arranged in the uppermost stream among the plurality of roll pairs 3.
The molten steel superheat degree ΔT [° C.] is an index of the temperature of the molten steel poured into the mold 1.
The specific water amount Wt [L / kg Steel] means the volume of cooling water used for 1 kg of steel.
In-mold electromagnetic stirring strength M-EMS [gauss] is an index of the strength of the magnetic field applied to stir the molten steel in the mold 1.

Next, specific operating conditions for continuous casting to which the present invention is applied will be described.
-Mold width W [mm] shall be 1200-2100.
-Casting speed Vc [m / min] shall be 1.4-2.8.
The slab to be cast is a so-called slab having an slab cross-sectional aspect ratio of 2 or more.
The immersion nozzle 2 is a so-called two-hole type in which a pair of opposed molten steel discharge holes are formed.

  Next, the structure of the immersion nozzle 2 will be described with reference to FIG. FIG. 2 is a perspective view of the immersion nozzle. As shown in FIG. 2A, the immersion nozzle 2 used in the present embodiment has a bottomed cylindrical shape, and a pair of opposed molten steel discharge holes 5 are formed slightly above the inner bottom 6. Two-hole type. As shown in FIG. 2 (b), the pair of molten steel discharge holes 5 has a downward angle θ [deg.] Of the molten steel discharge flow from the molten steel discharge holes 5. ] Is set obliquely downward from the inner periphery to the outer periphery so that it is set to 15 to 45 with respect to the horizontal. This downward angle θ [deg. ] Corresponds to the angle between the lower end line 5a (the contour of the lower end) of the molten steel discharge hole 5 and the horizontal specified in the vertical section of the immersion nozzle 2 in this embodiment. And the intersection of this lower end line 5a and the axis 2a of the immersion nozzle 2 is defined as a virtual intersection P.

  As shown in FIG. 3, the immersion nozzle 2 is set vertically in the mold 1 such that a pair of molten steel discharge holes 5 face the mold narrow surface 1a. In other words, the immersion nozzle 2 is set vertically in the mold 1 so that the flow of molten steel discharged from the pair of molten steel discharge holes 5 is perpendicular to the mold narrow surface 1a in plan view. In this state, when molten steel is poured from the immersion nozzle 2 into the mold 1, the molten steel flow from the immersion nozzle 2 first becomes obliquely downward, and eventually, when it collides with the mold narrow surface 1 a, it branches in the vertical direction, so An upward flow Q and a downward flow R are formed. Of these, the upward flow Q plays a role of preventing the so-called skinning in which the surface is solidified by supplying heat to the molten steel near the meniscus. In the present embodiment, molten steel is poured into the mold 1 and a predetermined molten metal surface level is obtained, so that the virtual intersection point P is 150 to 350 [mm] below the meniscus. The relative vertical installation position of the immersion nozzle 2 is adjusted.

  Next, the structure of the mold 1 will be described in more detail with reference to FIG. As shown in FIG. 3A, the mold 1 according to this embodiment is configured for a so-called slab in which a cast slab has a rectangular cross section and an aspect ratio of 2 or more. The mold 1 is disposed between a pair of opposed wide-surface mold copper plates 7 and the wide-surface mold copper plate 7 and supports a pair of opposed narrow-surface mold copper plates 8 and the wide-surface mold copper plate 7 from the back side. The wide-surface mold back frame 9, the narrow-surface mold back frame 10 that supports the narrow-surface mold copper plate 8 from the side, and the narrow-surface mold copper plate 8 and the narrow-surface mold back frame 10 are advanced and retracted in the mold width direction. For this reason, the narrow surface mold driving device 11 is mainly configured. In the present embodiment, the narrow side mold copper plate 8 and the narrow side mold back frame 10 are sandwiched between the narrow side mold driving device 11 and the narrow side mold back frame 10. Permanent magnet 12 is installed in the remaining space. The permanent magnet 12 is provided so that the main direction of the magnetic field formed by the permanent magnet 12 is parallel to the mold width direction. In this embodiment, as an example, the N poles of the permanent magnets 12 are arranged so as to face each other. This is because the magnetic field in one narrow surface does not affect the magnetic field in the other narrow surface. Of course, the N pole and the S pole may be arranged to face each other. In this figure, the white arrow is an image of a main magnetic field formed in the molten steel by the permanent magnet 12 described above.

  Next, the magnetic field will be described in more detail. In the present embodiment, when the magnetic flux density is measured at the center of the mold thickness direction on the mold narrow surface 1a in the following magnetic field application region, the perpendicular component B [T] with respect to the mold narrow surface 1a is 0.05 or more. Is set to be The magnetic field application region is an application end position M2 as a position where the meniscus distance M [mm] is 300 to 500 from an application start position M1 [mm] where the meniscus distance M [mm] is 100 to 300. This is a region where the distance ΔM3 [mm] from the application start position M1 [mm] to the application end position M2 [mm] is 150 to 400 until reaching [mm]. In FIG. 3, the vertical region indicated by the symbol ΔM3 has an overlapping relationship with the permanent magnet 12, but the vertical region indicated by ΔM3 means the vertical length of the permanent magnet 12. It should be noted that this means a region where a magnetic field having a predetermined magnetic flux density or more is to be formed.

  Next, the effect | action by forming said magnetic field is demonstrated based on FIG. FIG. 4 is a diagram for explaining the action of the magnetic field on the upward flow. In this figure, the code | symbol B shows the perpendicular | vertical component with respect to the mold narrow surface 1a of said magnetic field. As shown in the figure, an induced current I in the mold thickness direction is generated in the molten steel forming the upward flow Q by the vertical component B [T] of the magnetic field with respect to the mold narrow surface 1a. Due to the vertical component B [T], the braking force F directed in the direction opposite to the upward flow Q acts on the molten steel, and thus the upward flow Q is braked. Since this braking force acts greatly in proportion to the flow rate of the upward flow Q, uneven flow of the molten steel discharge flow is also suppressed. As a result, it is possible to avoid a significant solidification delay that is a cause of a breakout directly under the mold and a powder entrainment that is a cause of a product sliver defect.

  Hereinafter, the test for confirming the technical effect of the continuous casting method of the slab according to the present embodiment will be described. Each numerical range described above is reasonably supported by the following confirmation test.

<< Test 1.1: Indicator >>
First, an index used for evaluation of each confirmation test will be described.
<Powder defect>
FIG. 5 is a performance graph showing the correlation between powder entrainment defects and sliver defects. That is, the horizontal axis represents the oxide caused by the entrainment of powder detected by visual inspection of the cut surface obtained by hot scarfing the front and back surfaces (reference surface and anti-reference surface) of the slab having a weight of about 30 tons by about 1.5 mm. This is the maximum value of the width (thickness) of the contained defect. The vertical axis represents the frequency of occurrence of sliver due to powder entrainment defects that appears when a slab cast under the same casting conditions as the above slab is hot rolled into a pickled coil product. That is, the product coil to be inspected (coil length = 1000 m to 3000 m, the coil length is determined by how much the slab of about 11 to 12 m is rolled, that is, the thickness of the product coil.) It is the ratio of the number of product coils in which sliver due to powder entrainment defects is detected to the total number. According to FIG. 5, when the maximum value of the oxide-containing defect width caused by the entrainment of powder detected on the front and back surfaces of the slab at the stage where the hot scarf is carried out is 3 mm or more, the pickled product is the vertical axis. It can be seen that the sliver index soars. Therefore, regarding powder entrainment, the surface of the slab is defined as “× (defect)” when an oxide-containing defect having a width of 3 mm or more is detected by visual inspection at the time of the hot scarf, and “◯ (good)” when it is not. Quality was evaluated. Note that the above powder entrainment is likely to be a problem when continuously casting low carbon steel at a high casting speed Vc [m / min].
<Degree of solidification delay Cg [%]>
Reference is now made to FIG. FIG. 6 is an explanatory diagram of the solidification delay degree Cg [%]. This degree of solidification delay Cg [%] can be specified at each corner of the slab based on a negative segregation line that can be visually recognized on the cut surface obtained by cutting the slab perpendicularly to the casting direction. The degree Cg [%] is obtained based on the following formula (1). However, in the following formula (1), A [mm] is the distance between the negative segregation line and the wide mold surface at a point 5 [cm] away from the mold narrow surface, and B [mm] is the negative segregation line as the mold. This is the distance between the negative segregation line and the mold wide surface at the point closest to the wide surface.

  Next, please refer to FIG. FIG. 7 shows solidification delay Cg and B. O. It is a graph based on the results about the relationship with the occurrence frequency. That is, a casting mold having a carbon content C [wt%] of molten steel of 0.08 to 0.20 and a mold width W [mm] of 1800 or less and a casting speed Vc [m / min] of 1.5 or more is used. As a result of measuring the solidification delay Cg [%] at all corners of the slab for a total of 3 times for each charge, 12 (= 3 × 4) solidification delay Cg [ %], The highest degree of coagulation delay Cg [%] was divided every 5 [%] on the horizontal axis. Here, “40” on the horizontal axis means “40 to 45”. Then, the above continuous casting was repeated so that the number of samples (number of data, number of charges divided by frequency) was at least 10 or more for each frequency. When the above-mentioned sample number is satisfied for all frequencies, (number of charges classified into the frequency) is used as the denominator for each frequency (of the number of charges classified into the frequency, BO immediately under the template is generated) The ratio of the number of charges) as a molecule is shown on the vertical axis as “BO occurrence frequency [%] directly under the template”. According to this figure, if the solidification delay degree Cg [%] is operated so as to be less than 40, B. O. It can be seen that the occurrence of this can be prevented. In this sense, hereinafter, “significant solidification delay” in the present specification means ““ solidification delay with a solidification delay degree Cg [%] of 40 or more ””.

≪Test 1.2: Common test method≫
Next, a test method common to each confirmation test will be described.
The cast slab is cut approximately every 12.5 m perpendicular to the casting direction, and the solidification delay Cg [%] is measured at the four corners on this cut surface. Then, a total of 16 solidification delay degrees Cg [%] are obtained in each test by using four cut surfaces as measurement objects.
・ Select one piece of steel obtained from the above cutting at random, and visually observe the front and back surfaces with a hot scarf of about 1.5 mm, and determine the width (thickness) of the oxide-containing defect caused by the powder entrainment. Record.

≪Test 1.3: Common test conditions≫
Next, test conditions common to each confirmation test will be described.
The immersion nozzle 2 is a two-hole type in any test.
The mold height H [mm] is 900.

≪Test 1.4: Individual test conditions and test results≫
Next, individual test conditions and test results of each confirmation test are shown in Table 1 below. In Table 1 below, the column title “D” means the mold thickness D [mm]. The column title “W” means the mold width W [mm]. The column title “Vc” means the casting speed Vc [m / min]. The column title “C” means the carbon content C [wt%]. The column title “θ” indicates the downward angle θ [deg. ] Setting value. The column title “installation position” means the installation position of the magnetic field generator, and “short side center” means that the magnetic field generator is provided at the center in the mold thickness direction as shown in FIG. On the other hand, the “corner portion” indicates that the magnetic field generators are arranged in two in the mold thickness direction as shown in FIG. The column title “B” is a vertical component B [T] of the magnetic field formed by the magnetic field generator with respect to the mold narrow surface 1a. In the column title “Cg”, the largest data among the data of the 16 solidification delay Cg [%] obtained in each test was entered. Finally, as a comprehensive judgment, when both the evaluation regarding the powder defect and the evaluation regarding the solidification delay degree Cg [%] were both good, the test was evaluated as “◯ (good)”, and at least one of them When one evaluation was not good, the test was evaluated as “x (defect)”.

<< Test 1.5: Discussion >>

  According to Table 1 above, according to the continuous casting method of a slab according to the present embodiment, it can be seen that a significant solidification delay that is a cause of a mold direct breakout and a powder entrainment that is a cause of a product sliver defect can be avoided. .

  In the following, Table 1 will be discussed further.

  The reason why the mold width W [mm] is set to 1200 or more is from the viewpoint of productivity, and the reason why the mold width is set to 2100 or less is that the equipment cost increases despite a small demand.

  The reason why only the continuous casting with the casting speed Vc [m / min] of 1.4 or higher is targeted is that if it is less than 1.4, powder entrainment and significant solidification delay are less likely to be a problem in the first place. . In addition, Test No. According to No. 33, when the casting speed Vc [m / min] exceeds 2.8, even if the continuous slab casting method according to this embodiment is applied, powder entrainment that causes product sliver defects is no longer possible. Therefore, the upper limit of the casting speed Vc [m / min] was set to 2.8.

  The downward angle θ [deg. ] Is only 15 for continuous casting, if it is less than 15, the molten steel flow velocity in the vicinity of the meniscus of the immersion nozzle 2 is large, and powder entrainment is likely to occur dramatically. On the other hand, the downward angle θ [deg. ] Is only 45 or less for continuous casting, if it exceeds 45, heat supply to the meniscus is insufficient, so-called skinning occurs in which the molten steel near the meniscus is solidified. This is because it has a great adverse effect.

  When the distance M4 [mm] between the meniscus and the virtual intersection P is only 150 or more, if it is less than 150, it is immersed by the negative pressure near the upper end of the molten steel discharge hole 5 of the immersion nozzle 2 This is because the powder around the nozzle 2 is entrained in the molten steel discharge flow, causing significant powder entrainment. On the other hand, only the continuous casting in which the distance M4 [mm] is 350 or less is used. When the distance M4 exceeds 350, the heat supply to the meniscus becomes insufficient, and the same skinning problem as above occurs. This is because the immersion nozzle 2 has to be lengthened, and the refractory cost increases accordingly.

  Now, the measurement position of the vertical component B [T] of the magnetic flux density of the magnetic field described above is set at the center in the mold thickness direction of the mold narrow surface 1a because the flow velocity of the upward flow Q is at the center in the mold thickness direction. Because it becomes the maximum. Note that the installation location of the magnetic field generator is arbitrary. 1 to 39, the center of the short side may be used. 40 may be a corner portion. However, test no. Rather than disperse the magnetic field generator into two in the mold thickness direction as shown in FIG. It is preferable to concentrate and install at the center of the mold thickness direction as in 1 to 39 in that a large vertical component B [T] is easily secured.

  The reason why only the vertical component B [T] with respect to the mold narrow surface 1a of the magnetic flux density of the magnetic field is focused is that the horizontal component with respect to the mold narrow surface 1a hardly functions as a braking force against the upward flow Q. This is because according to the horizontal component with respect to the mold narrow surface 1a, an induced current in a direction perpendicular to the mold narrow surface 1a is generated in the molten steel forming the upward flow Q. However, there is an insulating mold powder or air gap between the mold narrow surface 1a and the shell, which prevents the current from flowing in a direction perpendicular to the mold narrow surface 1a. Therefore, an induced current in a direction perpendicular to the mold narrow surface 1a is hardly generated.

  Test No. According to 25 to 27, the lower limit value of the vertical component B [T] necessary for suppressing the flow velocity of the upward flow Q can be determined to be approximately 0.05. In this embodiment, even with such a small vertical component B [T], it is possible to avoid a significant solidification delay that is a cause of a mold-type breakout and a powder squeeze that is a cause of a product sliver defect. Since the slab continuous casting method according to the present invention can make the size of the magnetic field generator (permanent magnet or electromagnet) necessary for forming the magnetic field extremely compact, even when the installation space of the magnetic field generator is extremely limited The slab continuous casting method according to this embodiment can be easily introduced.

  Test No. As is clear from FIGS. 5 and 10, when the application start position M1 [mm] of the magnetic field application region is deeper than 300, a sufficient braking effect cannot be obtained. This is because the position where the flow velocity of the upward flow Q is the fastest in the vicinity of the mold narrow surface 1a is a relatively shallow region from the meniscus to about 400 mm. Therefore, if the magnetic field is not applied at this position, the upward flow Q is effectively used. This is probably because braking is not possible. Therefore, it is necessary to set the application start position M1 [mm] of the magnetic field application region to a position within 300 mm from the meniscus. However, test no. As is apparent from 1 and 6, even when a magnetic field is applied directly below the meniscus, a sufficient effect cannot be obtained. The reason for this is considered to be that, immediately below the meniscus from the meniscus to 100 mm, even when no magnetic field is applied, the flow rate of the upward flow Q is small in the first place, so that the braking effect by applying the magnetic field is weak. Therefore, the application start position M1 [mm] in the magnetic field application region needs to be 100 or more.

  Test No. 11 and 12, when the application end position M2 [mm] of the magnetic field application region is less than 300, the flow suppression effect is not sufficient, and the test No. When the application end position M2 [mm] of the magnetic field application region is 300 as in FIG. 13, a sufficient flow suppression effect is obtained, and in order to effectively suppress the upward flow Q, the application end of the magnetic field application region It can be seen that the position M2 [mm] needs to be 300 or more. In addition, Test No. When the application end position M2 [mm] in the magnetic field application region exceeds 500 as in 5, 9, 10, 16 and so on, a powder defect has occurred, and in order to suppress the upward flow Q, the application end position M2 [mm] ] Need to be 500 or less. Since the position where the molten steel discharge flow collides with the mold narrow surface 1a is often around 600 mm below the meniscus, there is a possibility that the flow is unstable when the collision position is close to the lower end of the magnetic field application region. The

  Test No. in which both the application start position M1 [mm] and the application end position M2 [mm] in the magnetic field application region are within the appropriate range. 17 and 18, the test No. 1 in which the vertical distance ΔM3 [mm] of the magnetic field applying region is only 100 is obtained. In Test No. 18, a powder defect occurred, whereas a distance ΔM3 [mm] of the magnetic field application region of 150 was secured. 17, the generation of powder defects can be suppressed. Therefore, it can be seen that the distance ΔM3 [mm] of the magnetic field application region needs to be secured 150 or more. Regarding the upper limit value of the distance ΔM3 [mm] of the magnetic field application region, the maximum value that can be taken when both the application start position M1 [mm] and the application end position M2 [mm] of the magnetic field application region are set within an appropriate range. It was.

  As described above, in the above-described embodiment, the mold 1 having a mold width W [mm] of 1200 to 2100 is used, and a pair of opposed molten steel discharge holes 5 is formed. Downward angle θ [deg. ] Is set to 15 to 45 on the basis of the horizontal, the lower end line 5a of the molten steel discharge hole 5 specified by the vertical section of the immersion nozzle 2, the axis 2a of the immersion nozzle 2, Is immersed in molten steel so that the virtual intersection P is 150 to 350 [mm] below the meniscus, and the casting speed Vc [m / min] is 1.4 to 2.8. It is done by the method like. When the magnetic flux density is measured at the center of the mold thickness direction on the mold narrow surface 1a, a magnetic field having a vertical component B [T] of 0.05 or more with respect to the mold narrow surface 1a is set to a meniscus distance M [mm] of 100 to 100. From the application start position M1 [mm] as a position set to 300 to the application end position M2 [mm] as a position where the meniscus distance M [mm] is set to 300 to 500, in addition, the application start position M1 [mm] ] To the application end position M2 [mm], the distance ΔM3 [mm] is 150 to 400, respectively. According to the above method, since the magnetic field has a component perpendicular to the mold narrow surface 1a, the molten steel flow discharged from the immersion nozzle 2 collides with the mold narrow surface 1a and branches, so-called upward. The braking force acts on the upward flow Q efficiently. Further, since this braking force acts greatly in proportion to the flow rate of the upward flow Q, there is also an effect of suppressing the drift of the molten steel discharge flow. Further, since the braking force acts on the upward flow Q and the uneven flow is suppressed, it is possible to avoid a significant solidification delay that is a cause of the mold-type breakout and a powder entrainment that is a cause of a product sliver defect. Therefore, a high casting speed can be realized, thereby contributing to high productivity.

  In addition, within the above casting condition range, when the mold width W [mm] is small, the magnetic field application region is closer to the meniscus, and when the mold width W [mm] is large, the magnetic field application region is further from the meniscus. The magnetic field application region may be moved up and down according to the size of the mold width W [mm], such as away from it.

Schematic diagram of continuous casting machine Perspective view of immersion nozzle Cross section of mold Diagram for explaining the effect of magnetic field on upward flow Performance graph showing the correlation between powder entrainment defects and sliver defects Illustration of solidification delay Cg [%] Solidification delay Cg and directly below the mold O. Graph based on actual results of the relationship with the frequency of occurrence It is a figure similar to FIG. 3, Comprising: The figure which shows the other installation aspect of a magnetic field generator

Explanation of symbols

1 Mold 2 Immersion nozzle 5 Molten steel discharge hole 100 Continuous casting machine

Claims (1)

Using a mold having a mold width W [mm] of 1200 to 2100,
A two-hole type in which a pair of opposed molten steel discharge holes are formed, and a downward angle θ [deg. ] Is set to 15 to 45 on the basis of the horizontal, the virtual intersection of the lower end line of the molten steel discharge hole specified by the vertical section of the immersion nozzle and the axis of the immersion nozzle is from the meniscus. Immerse it in the molten steel to be 150-350 [mm] downward,
The casting speed Vc [m / min] is set to 1.4 to 2.8.
In the slab continuous casting method,
When the magnetic flux density is measured at the center of the mold thickness direction on the mold narrow surface, a magnetic field having a vertical component B [T] of 0.05 or more with respect to the mold narrow surface,
From the application start position M1 [mm] as a position where the meniscus distance M [mm] is 100 to 300,
Until the application end position M2 [mm] as a position where the meniscus distance M [mm] is 300 to 500,
In addition, the distance ΔM3 [mm] from the application start position M1 [mm] to the application end position M2 [mm] is 150 to 400.
Forming each one,
A method for continuously casting a slab in which a static magnetic field is applied to an ascending flow of a mold narrow surface.

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