JP5079681B2 - Continuous casting equipment for slab in which static magnetic field acts on upward flow of molten steel in mold - Google Patents

Description

  The present invention relates to a slab continuous casting facility in which a static magnetic field acts on an upward flow of molten steel in a mold.

  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, none of the documents mentions a so-called upward flow that flows upward as the molten steel flow discharged from the immersion nozzle collides with the narrow surface of the mold. 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 found that the direct mold-type breakout and product sliver defects, which are serious operational problems, are closely related to the above upward flow after intensive studies. The present invention has been made in view of such various points, and a main object of the present invention is to provide a technique for avoiding a mold-type breakout / product sliver defect caused by an upward flow of molten steel in a 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 the aspect of the present invention, a mold for cooling molten steel to form a solidified shell having a predetermined shape and a pair of molten steel discharge holes facing in the mold width direction are formed to pour molten steel into the mold. The continuous casting equipment for a slab is provided as follows, and the separation distance Lme [mm] between the upper end of the mold and the meniscus is 100 to 150 . That is, a permanent magnet for forming a magnetic field having a component perpendicular to the narrow surface is provided on the back surface of the narrow surface mold constituting each narrow surface of the mold. The distance Lu [mm] from the upper end of the mold to the upper end of the permanent magnet is 200 to 400. A distance Ld [mm] from the upper end of the mold to the lower end of the permanent magnet is 400 to 600. The distance Lmag [mm] from the upper end to the lower end of the permanent magnet is 150 to 400. The ratio dmag / D between the mold thickness D [mm] of the mold and the permanent magnet thickness dmag [mm] in the mold thickness direction of the permanent magnet is 0.75 to 1. The immersion nozzle is a two-hole type in which a pair of opposed molten steel discharge holes are formed, and the downward angle θ [deg.] Of the molten steel discharge flow from the molten steel discharge holes. ] Is set to 15 to 45 on the basis of the horizontal, the molten steel discharge hole specified by a vertical cross section passing through the axis of the immersion nozzle and in which the two pairs of opposed molten steel discharge holes appear. It is used by being immersed in molten steel so that the virtual intersection of the lower end line and the axis of the immersion nozzle is 150 to 350 [mm] below the meniscus. Thus, a sufficiently large permanent magnet is disposed at a position specified by the distances Lu [mm] and Ld [mm], and the permanent magnet forms a magnetic field having a component perpendicular to the narrow surface. Therefore, the molten steel flow discharged from the immersion nozzle collides with the narrow surface and branches, and the braking force efficiently acts on the so-called upward flow that goes upward. 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 slab casting facility. First, based on this figure, the structure and operation | movement of the continuous casting installation 100 are demonstrated easily as an example.

  The continuous casting equipment 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 configuration of the mold 1 will be described in detail later with reference to FIG. 3, and the configuration of the immersion nozzle 2 will be described in detail later with reference to FIG. 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 downstream 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 equipment 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 equipment 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. The “upper end of the mold 1” will be described later in detail with reference to FIG.
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, a specific configuration of the continuous casting equipment 100 will be described.

  That is, the slab to be cast by the continuous casting equipment 100 is a so-called slab having an aspect ratio of the slab cross section of 2 or more. The immersion nozzle 2 is a so-called two-hole type in which a pair of molten steel discharge holes facing in the mold width direction are formed in order to pour molten steel into the mold 1.

<Configuration of immersion nozzle 2>
Next, the configuration 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 1a, it branches in the vertical direction. 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. In FIG. 3, a symbol Lsn indicates a separation distance between the virtual intersection P and the meniscus.

  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 opposed to a pair, a wide surface mold 7 that forms the wide surface of the mold 1, and a narrow surface mold 8 that is disposed between the wide surface mold 7 and that faces the pair and forms the narrow surface of the mold 1. A mold frame 9 that supports the wide-surface mold 7 and the narrow-surface mold 8 is provided as a main configuration. Each wide surface mold 7 is a molten steel side wide surface mold copper plate 10 and a wide surface mold back plate 11 that is in close contact with the back surface of the wide surface mold copper plate 10 and forms a cooling channel (not shown) between the wide surface mold copper plate 10 and Consists of Similarly, each narrow-surface mold 8 is in close contact with the narrow-surface mold copper plate 12 on the molten steel side and the back surface of the narrow-surface mold copper plate 12 to form a cooling channel (not shown) between the narrow-surface mold copper plate 12. And a narrow mold back plate 13. A rod 14 of a hydraulic cylinder (not shown) provided on the mold frame 9 is connected to the upper and lower ends of the narrow mold back plate 13. With this configuration, by appropriately moving the rod 14 back and forth in the mold width direction, the mold width W [mm] that can be specified as shown in FIG. The taper angle of the so-called narrow surface taper achieved by narrowing the distance between the narrow surface mold copper plates 12 downward can be freely increased or decreased.

  And in this embodiment, the permanent magnet for forming the magnetic field which has a perpendicular | vertical component with respect to the mold narrow surface 1a on the back surface of the narrow surface mold 8 constituting each mold narrow surface 1a (narrow surface) of the mold 1 18 are provided. Further, a yoke 19 is coupled to the back surface of the permanent magnet 18, and the yoke 19 is moved in the vertical direction of the mold 1 by a yoke guide 20 bridged between the upper end and lower end of the narrow mold back plate 13. Guidance is possible. A compression coil spring 21 is interposed between the yoke guide 20 and the lower end of the narrow mold back plate 13, while the upper end of the narrow mold back plate 13 can be advanced and retracted in the vertical direction. A screw 22 is provided. With this configuration, when the screw 22 is advanced and retracted in the vertical direction of the mold 1, the yoke 19 that is urged above the mold 1 by the compression coil spring 21 and abuts against the lower end of the screw 22 causes the screw 22 to advance and retract. In conjunction with this, the mold 1 moves up and down. Since the above-described permanent magnet 18 is coupled to the yoke 19, that is, the position of the permanent magnet 18 in the vertical direction of the mold 1 can be freely adjusted by appropriately moving the screw 22 back and forth.

  Next, the material of the component of the mold 1, the path of the magnetic field generated by the permanent magnet 18, the arrangement position and the size of the permanent magnet 18 will be described.

<Constituent materials>
Mold frame 9: ferromagnetic steel (for example, S45C)
Wide surface mold copper plate 10: Copper wide surface mold back plate 11: Non-magnetic austenitic stainless steel narrow surface mold copper plate 12: Copper narrow surface mold back plate 13 (however, a magnet front surface portion 13a that is sandwiched between the permanent magnet 18 and molten steel) :) Non-magnetic austenitic stainless steel narrow mold back plate 13 magnet front surface portion 13a: ferromagnetic steel (for example, S45C)
Hydraulic cylinder and rod 14: Ferromagnetic steel (for example, S45C)
Permanent magnet 18: Preferably a samarium cobalt magnet (neodymium magnet or alnico magnet may be used).
Yoke 19: Ferromagnetic steel (for example, S45C)

<Path of magnetic field>
The permanent magnet 18 is provided so that the main direction of the magnetic field to be formed is parallel to the mold width direction. That is, the N pole and S pole of each permanent magnet 18 are arranged along the mold width direction. For example, the N poles (or S poles) of each permanent magnet 18 face each other with the molten steel interposed therebetween. Alternatively, the N pole and the S pole of each permanent magnet 18 face each other with the molten steel interposed therebetween. In FIG. 3A, a magnetic path achieved by appropriately selecting the material of the constituent elements of the mold 1 is indicated by a two-dot chain line and a symbol Y. As shown in FIG. 3 (a), the magnet front surface portion 13a, the yoke 19, the hydraulic cylinder and rod 14, and the mold frame 9 of the narrow surface mold back plate 13 are made ferromagnetic, while the wide surface mold back plate 11, By making the narrow mold back plate 13 (except the magnet front surface portion 13a, which is a part sandwiched between the permanent magnet 18 and molten steel) non-magnetic, the magnetic path in the mold 1 can be changed within each back plate. There is no problem of short circuiting and it does not reach the molten steel, and it passes through the deep part in the molten steel. In FIG. 3B, the white arrow is an image of a main magnetic field formed in the molten steel by the permanent magnet 18.

<Location and size of permanent magnet 18>
As shown in FIG. 3B, the distance Lu [mm] from the upper end of the mold 1 to the upper end of the permanent magnet 18 is set to 200 to 400. Here, “the upper end of the mold 1” means the lower upper end of the upper end of the wide-surface mold copper plate 10 and the upper end of the narrow-surface mold copper plate 12. As shown in FIG. 3B, in the present embodiment, the upper end of the narrow mold copper plate 12 is positioned lower than the upper end of the continuous casting equipment 100, so “the upper end of the mold 1” in the present embodiment. Indicates the upper end of the narrow mold copper plate 12. Similarly, the distance Ld [mm] from the upper end of the mold 1 to the lower end of the permanent magnet 18 is set to 400 to 600. The distance Lmag [mm] from the upper end to the lower end of the permanent magnet 18 is 150 to 400, the mold thickness D [mm] of the mold 1 and the permanent magnet thickness dmag [mm] in the mold thickness direction of the permanent magnet 18; The ratio dmag / D is 0.75 to 1.

<Magnetic flux density>
Next, the magnetic field realized by the above configuration will be described quantitatively. That is, according to the above configuration, when the magnetic flux density is measured at the center of the mold thickness direction on the mold narrow surface 1a, in the region facing the permanent magnet 18 in the mold width direction, the vertical component Bnc with respect to the mold narrow surface 1a. [T] is 0.05 or more.

<Action by magnetic field>
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 symbol Bnc indicates a vertical component of the magnetic field with respect to the mold narrow surface 1a. 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 Bnc [T] of the magnetic field with respect to the mold narrow surface 1a. Due to the vertical component Bnc [T], the braking force F directed in the opposite direction 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 equipment 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 is 3 mm or more at the stage where the hot scarf is performed, the pickled product is a 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 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 slab wide surface at a point 5 [cm] away from the mold narrow surface, and B [mm] is the negative segregation line. It is the distance between the negative segregation line and the slab wide surface at the point closest to the mold 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, by using the four cut surfaces as measurement objects, a total of 16 solidification delay degrees Cg [%] are obtained in each confirmation test.
・ 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 entrainment of powder. Record.

≪Test 1.3: Common test conditions≫
Next, test conditions common to each confirmation test will be described. In short, the continuous casting of the slab according to this confirmation test is a two-hole type in which a mold 1 having a mold width W [mm] of 1200 to 2100 is used and a pair of opposed molten steel discharge holes 5 are formed. , Downward angle θ of the molten steel discharge flow from the molten steel discharge hole 5 [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 the molten steel so that the virtual intersection P is 150 to 350 [mm] below the meniscus, the separation distance Lme [mm] between the upper end of the mold 1 and the meniscus is set to 100 to 150, and the casting speed Vc [m / min]. ] Is 1.4 to 2.8.

Specifically, it is as follows.
The immersion nozzle 2 is a two-hole type in any test.
The mold height H [mm] is 900.
The permanent magnet 18 is arranged at the center in the mold thickness direction.
-Mold width W [mm] shall be 1200-2100. Note that if the mold width W [mm] is 1200 or more, it is excellent from the viewpoint of productivity, while if it exceeds 2100, only the equipment cost rises despite a small demand. Since the mold 1 of this size has a high throughput, powder defects and a significant solidification delay are likely to occur as compared with the case of casting billets and blooms.
-Casting speed Vc [m / min] shall be 1.4-2.8. If the casting speed Vc [m / min] is less than 1.4, powder entrainment and significant solidification delay are rarely a problem in the first place.
-The steel grade shall be ultra low carbon steel, low carbon steel and medium carbon steel. That is, the carbon content C [wt%] is set to 0.00015 to 0.25.
-Downward angle θ [deg. ] Is 15 to 45. The downward angle θ [deg. ] Is less than 15, the flow rate of molten steel near the meniscus of the immersion nozzle 2 is large, and powder entrainment is likely to occur dramatically, while the downward angle θ [deg. ] Exceeds 45, the supply of heat to the meniscus is insufficient, so-called skinning occurs where the molten steel in the vicinity of the meniscus is solidified, which has a significant adverse effect on continuous casting.
The distance Lsn [mm] between the virtual intersection P and the meniscus is 150 to 350. If the separation distance Lsn [mm] is less than 150, the negative pressure near the upper end of the molten steel discharge hole 5 of the immersion nozzle 2 causes the powder around the immersion nozzle 2 to be caught in the molten steel discharge flow, causing significant powder entrainment, On the other hand, if the separation distance Lsn [mm] exceeds 350, the supply of heat to the meniscus is insufficient, and the same skinning problem as described above occurs, and the immersion nozzle 2 must be lengthened. Refractory costs increase.
The separation distance Lme [mm] between the upper end of the mold 1 and the meniscus is 100 to 150. This numerical range is generally adopted. Note that if the separation distance Lme [mm] is less than 100, there is a concern about overflow. On the other hand, if the separation distance Lme [mm] exceeds 150, the solidified shell at the lower end of the mold is relatively thin, so that a breakout directly under the mold is performed. It is shunned from the viewpoint of prevention. In the latter case, the immersion nozzle 2 must be lengthened accordingly, so that the refractory cost is avoided.
The thickness of the permanent magnet 18 in the mold width direction is 130 [mm]. The thickness of the permanent magnet 18 in the mold width direction is preferably 80 to 160 [mm], more preferably 120 to 140 [mm].

≪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 “W” means the mold width W [mm]. The column title “D” means the mold thickness D [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 “Lsn” means a separation distance between the virtual intersection P and the meniscus shown in FIG. The column title “magnet” means whether or not the permanent magnet 18 is installed. The column title “Lme” means the separation distance between the upper end of the mold 1 and the meniscus shown in FIG. The column title “Lu” means the distance from the upper end of the mold 1 to the upper end of the permanent magnet 18. The column title “Ld” means the distance from the upper end of the mold 1 to the lower end of the permanent magnet 18. The column title “Lmag” means the distance from the upper end to the lower end of the permanent magnet 18. The column title “dmag” means the permanent magnet thickness of the permanent magnet 18 in the mold thickness direction. The column title “dmag / D” means the ratio between the mold thickness D [mm] of the mold 1 and the permanent magnet thickness dmag [mm] of the permanent magnet 18 in the mold thickness direction. The column title “Bnc” is a vertical component Bnc with respect to the mold narrow surface 1a in the region facing the permanent magnet 18 and the mold width direction when the magnetic flux density is measured on the mold narrow surface 1a and in the mold thickness direction center. It means the minimum value of [T]. The reason for paying attention to the magnetic flux density at the center in the mold thickness direction is that the flow velocity of the upward flow Q is maximized at the center in the mold thickness direction. Further, the vertical component Bnc [T] with respect to the mold narrow surface 1a is focused on because 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. 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)”.

  According to Table 1 above, according to the slab continuous casting equipment 100 according to the present embodiment, it can be seen that it is possible to avoid a significant solidification delay that is a cause of the mold-type breakout and powder entrainment that is a cause of product sliver defects. . In particular, test no. See test results 1-18, 34-38.

  In addition, Test No. 16, if the distance Ld [mm] from the upper end of the mold 1 to the lower end of the permanent magnet 18 is 700, the evaluation regarding the powder defect is poor. This is considered to be due to the following reasons. That is, the molten steel discharge flow discharged from the immersion nozzle 2 collides with the mold narrow surface 1 a and branches is generally at a point 700 [mm] below the upper end of the mold 1. If a magnetic field is formed at this branching point, it is apparent that the state of the upward flow Q becomes unstable.

  Moreover, the continuous casting equipment 100 according to the above embodiment is configured such that the installation position of the permanent magnet 18 can be finely adjusted in the vertical direction. Here, test no. When comparing 8 and 9, a slight improvement in the solidification delay was observed simply by finely adjusting the installation position of the permanent magnet 18 in the vertical direction. Therefore, if the continuous casting equipment 100 according to the above embodiment is used, continuous casting can be operated so as to obtain the best solidification delay.

(Summary)
(Claim 1)
As described above, in the above embodiment, the continuous casting equipment 100 is configured as follows. That is, permanent magnets 18 for forming a magnetic field having a component perpendicular to the narrow mold surface 1a are provided on the back surface of the narrow mold 8 constituting each narrow mold surface 1a of the mold 1. The distance Lu [mm] from the upper end of the mold 1 to the upper end of the permanent magnet 18 is 200-400. A distance Ld [mm] from the upper end of the mold 1 to the lower end of the permanent magnet 18 is 400 to 600. The distance Lmag [mm] from the upper end to the lower end of the permanent magnet 18 is 150 to 400. The ratio dmag / D between the mold thickness D [mm] of the mold 1 and the permanent magnet thickness dmag [mm] of the permanent magnet 18 in the mold thickness direction is 0.75 to 1. Thus, a sufficiently large permanent magnet 18 is arranged at a position specified by the distances Lu [mm] and Ld [mm], and the permanent magnet 18 has a component perpendicular to the mold narrow surface 1a. Since the magnetic field is formed, the molten steel flow discharged from the immersion nozzle 2 collides with the mold narrow surface 1a and branches, and the braking force efficiently acts on the so-called upward flow Q that moves upward. 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 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.

  The maximum value (400) of the distance Lmag [mm] from the upper end to the lower end of the permanent magnet 18 was determined based on the minimum value of the distance Lu [mm] and the maximum value of the distance Ld [mm].

  Although the preferred embodiments of the present invention have been described above, the above embodiments can be implemented with the following modifications.

  That is, for example, in the above embodiment, the permanent magnet 18 is a samarium cobalt magnet, but may be a neodymium magnet or an alnico magnet instead. Hereinafter, the reason will be described.

  As permanent magnets that are commonly used, there are neodymium magnets (Ne-Fe-B), samarium cobalt magnets (Sa: Co = 2: 17), ferrite magnets, and alnico magnets as shown in Table 2 below. The residual magnetic flux density, coercive force, heat resistant temperature, and Vickers hardness of these permanent magnets are as shown in Table 2 below. According to Table 2 below, the samarium-cobalt magnet is magnetically excellent, has good mechanical strength, and has stable magnetic properties in a high-temperature atmosphere where steam is generated. Most suitable as magnet 18.

  Similar to the samarium cobalt magnet, the neodymium magnet has both high residual magnetic flux density and coercive force, and has magnetic characteristics suitable for obtaining a large magnetic flux density in a limited installation space. However, neodymium magnets have the disadvantage of low heat resistance and rust. Since the permanent magnet 18 may be exposed to high-temperature steam, if a neodymium magnet is used as the permanent magnet 18, sufficient anti-corrosion measures such as Ni plating are implemented, and a water-cooled mold back plate is used. It is necessary to implement sufficient cooling measures such as close contact with the surface.

  On the other hand, alnico magnets are superior in characteristics other than holding force, but the holding force is extremely low compared to other magnets, so a thin magnet in the mold width direction is sufficient for self-demagnetization due to a demagnetizing field. Has a disadvantage that the magnetic flux density cannot be formed for the upward flow Q. If an alnico magnet is employed as the permanent magnet 18, it is necessary to secure a sufficient space on the back surface of the narrow mold 8 so that the permanent magnet 18 can be installed sufficiently thick in the mold width direction.

  However, ferrite magnets have the advantage of being inexpensive, but are difficult to adopt from the viewpoint of magnetic characteristics. In addition, the electromagnet requires more installation space than the permanent magnet, and it is difficult to adopt the electromagnet because it consumes electric power.

  In other words, within the above casting condition range, when the mold width W [mm] is small, the permanent magnet 18 is brought closer to the meniscus, and when the mold width W [mm] is large, the permanent magnet 18 is moved away from the meniscus. It is preferable to move the installation position of the permanent magnet 18 up and down according to the size of the mold width W [mm].

Schematic diagram of continuous casting equipment 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

Explanation of symbols

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

Claims (1)

A mold for cooling the molten steel to form a solidified shell of a predetermined shape;
An immersion nozzle in which a pair of molten steel discharge holes facing the mold width direction are formed in order to pour molten steel into the mold;
Equipped with a,
The distance Lme [mm] between the upper end of the mold and the meniscus is a slab continuous casting facility used as 100 to 150 ,
Permanent magnets for forming a magnetic field having a component perpendicular to the narrow surface are respectively provided on the back surfaces of the narrow surface molds constituting the narrow surfaces of the mold,
The distance Lu [mm] from the upper end of the mold to the upper end of the permanent magnet is 200 to 400,
The distance Ld [mm] from the upper end of the mold to the lower end of the permanent magnet is 400 to 600,
The distance Lmag [mm] from the upper end to the lower end of the permanent magnet is 150 to 400,
A template thickness D [mm] of the mold, the thickness permanent magnet DMAG [mm] in the mold the thickness direction of the permanent magnet, the ratio DMAG / D of I 0.75 der,
The immersion nozzle is a two-hole type in which a pair of opposed molten steel discharge holes are formed, and a downward angle θ [deg.] Of the molten steel discharge flow from the molten steel discharge holes. ] Is set to 15 to 45 on the basis of the horizontal, the molten steel discharge hole specified by a vertical cross section passing through the axis of the immersion nozzle and in which the two pairs of opposed molten steel discharge holes appear. It is used by being immersed in molten steel so that the virtual intersection of the lower end line and the axis of the immersion nozzle is 150 to 350 [mm] below the meniscus,
A slab continuous casting facility in which a static magnetic field acts on the upward flow of molten steel in a mold.

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