Technical field
[0001]
　The present invention relates to a continuous casting method of steel.
Background technique
[0002]
　Continuous casting of steel, the molten steel in the tundish is carried out while supplying into the mold of a continuous casting facility through the immersion nozzle. The molten steel is discharged into the mold from the discharge hole formed in the lower end of the immersion nozzle, is cooled in the mold is withdrawn from the mold outlet in a state where the solidified shell thickness so as not to break out is ensured. Solidified shell, after completely solidified are secondary cooling by spraying in the process of being withdrawn, disconnected, a slab.
[0003]
　As a technique for improving the cleanliness of the slab, for example, Patent Document 1, by opposing installing an electromagnetic stirrer in the long side meniscus proximity of the mold, to generate a swirl flow on the surface of the molten steel in the mold, this the washing effect of the swirling flow is a factor of the slab defects, inclusions and bubbles a phenomenon attached to the surface of the mold, suppressing technology is disclosed. In Patent Document 2, by the action of the electromagnetic brake in the discharge flow discharged from the discharge hole of the immersion nozzle, to suppress the lowering speed of the molten steel, inclusions in the molten steel to ensure the time for levitation techniques It has been disclosed.
[0004]
　However, in the technique of Patent Document 1, since the electromagnetic brake is not applied to the discharge flow discharged from the discharge hole of the immersion nozzle, the lowering speed of the discharge flow is not suppressed. Therefore, while inclusions and bubbles of alumina remaining in the molten steel is not sufficiently floated removed, there is a problem that caused the internal defects penetrate deep in the cast piece. This problem, as disclosed in Patent Document 2, can be avoided by the action of the electromagnetic brake in the discharge flow.
[0005]
　If allowed to act electromagnetic brake discharge flow, as shown in FIGS. 3 and (a front sectional view of the mold) 4 (side sectional view of the mold), upflow is generated along the immersion nozzle 2, the upward flow the downward flow is inverted in the vicinity of the surface of the molten steel. Here, in particular, in the mold for producing thin cast strip thicknesses, the distance between the long side surfaces of the mold (D 0 ) is closer. Therefore, inclusions and bubbles carried in the downward flow, the long side wall 3a constituting the long sides of the mold, in contact with the solidified shell 8 formed on the 3b, likely to be caught here, surface defects becomes a factor, a new problem arises.
CITATION
Patent Literature
[0006]
Patent Document 1: JP 2008-183597 Patent Publication
Patent Document 2: Japanese Patent No. 5245800
Summary of the Invention
Problems that the Invention is to Solve
[0007]
　An object of the present invention is to solve the conventional problems described above, while suppressing the internal defects by electromagnetic brake, to avoid the occurrence of surface defects caused by the electromagnetic brake, as compared with the prior art, cleaning of the slab it is to provide a technique capable of increasing the degree.
Means for Solving the Problems
[0008]
　In the present invention to solve the above problems, while applying an electromagnetic brake to the discharge flow discharged from the discharge hole of the immersion nozzle in a continuous casting method of steel supplying molten steel into the mold, a magnetic flux density of the electromagnetic brake (B) , the range of the following equation (1). Here, the magnetic flux density of the electromagnetic brake (B), means a magnetic flux density in the electromagnetic brake coil center.
B min ≦ B ≦ B max　　　　　... (Equation 1)
Here,
[0009]
[Number 1]

[0010]
[Number 2]

D 0 of the mold having short sides and long sides in = horizontal cross-sectional shape, the long side ends, the mold thickness is measured as the distance between the opposite long sides in the mold (m), D
max = horizontal the mold having short sides and long sides in cross section, in the long side center, the maximum value of the mold thickness is measured as the distance between the opposite long sides in the mold (m), H
0 electromagnetic brake coil from = the molten steel surface vertical distance to the center
(m), H SEN vertical distance from = immersion nozzle bottom surface to the center electromagnetic brake coil
(m), v = flow velocity of the discharged from the immersion nozzle molten steel (m / s),
theta = upward as positive, determined as the angle between a horizontal line, the discharge angle of molten steel (°).
[0011]
　In the above present invention, as a template, it is possible to use a rectangular mold having short sides and long sides in a horizontal cross-sectional shape.
[0012]
　In the above the present invention using a rectangular template as a template, the flow velocity v of the molten steel is preferably 0.685m / s ~ 0.799m / s. Thus, increased flow is gradually formed across, it becomes easy to suppress the formation of the descending flow along the solidification interface.
[0013]
　In the above present invention, as a template, having short sides and long sides in a horizontal cross-sectional shape, and the funnel mold the distance between opposite long sides in the mold, and expanded than the long side ends in the long side center it is preferably used.
[0014]
　In the above invention using a funnel mold as a template, D max / D 0 is preferably is 1.16 to 1.24. Thus, when the inclusions carried by downward flow also the inclusions becomes easy to reduce the frequency to be supplied to the solidification interface.
[0015]
　In the above invention using a funnel mold as a template, H SEN / H 0 is preferably is from 0.161 to 0.327. Thus, increased flow is gradually formed across, it becomes easy to suppress the formation of the descending flow along the solidification interface.
[0016]
　In the above invention using a funnel mold as the template, the flow velocity v of the molten steel is preferably 0.441m / s ~ 1.256m / s. Thereby, the molten steel flow in the mold is stabilized, it becomes easy to suppress the fluctuation of the molten steel surface.
[0017]
　In the above present invention, the jetting angle θ of the molten steel is preferably -45 ° ~ -5 °. Thereby, the molten steel flow in the mold is stabilized, it becomes easy to suppress the fluctuation of the molten steel surface.
Effect of the invention
[0018]
　While applying an electromagnetic brake to the discharge flow discharged from the discharge hole of the immersion nozzle in a continuous casting method of steel supplying molten steel into the mold, a magnetic flux density of the electromagnetic brake (B), the range of the equation (1) According to the present invention where the configuration to be, by suppressing the lowering speed of the molten steel, of reducing the internal defects of the steel strip, while enjoying the effect of the electromagnetic brake, for producing thin cast strip thicknesses even in the case of using the mold, it is possible to effectively avoid the occurrence of surface defects caused by the electromagnetic brake.
[0019]
　That is, according to the present invention, the the proper intensity electromagnetic brake according to (Equation 1), by an extremely simple method called, both internal defects and surface defects of the mold reliably reduce the cleanliness of the slab it can be increased.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020]
In one embodiment of FIG. 1 the present invention, is an explanatory diagram of a plan schematically showing for illustrating a schematic configuration of a mold vicinity of the continuous casting apparatus.
In one embodiment of FIG. 2 the present invention, is an explanatory view of the front section schematically showing for illustrating a schematic configuration of a mold vicinity of the continuous casting apparatus.
3 is a front sectional view illustrating a molten steel flow state in the mold when allowed to act the electromagnetic brake.
FIG. 4 is a side sectional view illustrating a molten steel flow state in the mold when allowed to act the electromagnetic brake.
DESCRIPTION OF THE INVENTION
[0021]
　Shows a preferred embodiment of the present invention are described below.
[0022]
　In the present embodiment, as shown in Figure 1, the mold 1 is horizontal cross-sectional shape that is substantially rectangular, arranged immersion nozzle 2 in the vicinity of substantially the center of the long sides and short sides, as shown in FIG. 2, the mold 1 on the outside of the long side wall 3 of the long side of the height position lower than the lower end of the immersion nozzle 2, the electromagnetic brake device 4 are disposed facing each other across the mold 1.
[0023]
　In the present embodiment, as shown in FIG. 1, it has short sides and long sides in a horizontal cross-sectional shape, and the long side the distance between the opposing in the mold, long side center (D max long side ends in) ) is used extended funnel mold than. Other, in the present invention, D max = D 0 may be used a rectangular mold is. Here, D max > D 0 With addition of a horizontal swirling flow in the vicinity of the molten steel surface can be stabilized, by distancing the solidified shell from the downward flow caused by reversed near the molten steel surface, inclusions and it is possible to reduce the acquisition opportunity of bubbles.
[0024]
　Of the immersion nozzle 2, the short side walls 7a of the mold 1, the portion facing the 7b, the discharge hole 5 for discharging the molten steel obliquely downward into the mold 1 are respectively formed. In the immersion nozzle 2, since the Ar gas is blown, the discharge flow 6 discharged from the discharge hole 5, the bubbles and the Ar gas include inclusions of alumina or slag system.
[0025]
　Bubbles and these Ar gas inclusions alumina or slag system is still not sufficiently floated removed in the mold 1, in order to avoid a phenomenon that the internal defects penetrate deep into the billet, in this embodiment , the height position lower than the lower end of the immersion nozzle 2, the electromagnetic brake device 4 are disposed facing each other across the mold 1.
[0026]
　Electromagnetic brake device 4 is configured by a magnet, against the discharge flow 6 immediately after being discharged from the discharge hole 5 of the immersion nozzle 2, the mold 1 long side walls 3a, the mold width direction along the 3b (FIG. 1 DC magnetic field having a substantially uniform magnetic flux density distribution over the X-direction) of the can be applied to short sides walls 7a, the mold thickness direction along 7b of the mold 1 (Y direction in FIG. 1). This DC magnetic field and the discharge flow, induced current is generated in the X direction in FIG. 1, the DC magnetic field of the this induced current, in the vicinity of the discharge flow 6, counter flow of the discharge flow 6 and opposite is formed , lowering speed of the molten steel is suppressed. Thus, it is possible to avoid a phenomenon in which inclusions and bubbles of alumina remaining in the molten steel to penetrate deep into the left billet not sufficiently floated removed.
[0027]
　In the prior art, when an acting an electromagnetic brake in the discharge flow, as shown in FIGS. 3 and 4, occurs upflow along the immersion nozzle 2, the upward flow is reversed in the vicinity of the surface of the molten steel flows downward Te. In particular, D 0 in the mold degree 400mm or less, inclusions and bubbles carried by the descending flow, the long side wall 3a, in contact with the solidified shell 8 on 3b likely to be trapped, liable to cause surface defects there was a problem. In contrast, in the present invention, by a proper strength magnetic flux density of the electromagnetic brake according to the above (Equation 1), inclusions and bubbles carried by the descending flow, the long side wall 3a, the solidified shell 8 on 3b the phenomenon is captured to enable suppression.
[0028]
　Above (Equation 1) has been guided by various studies of the inventors, the combination of all the elements constituting the equation (1), in which the first time, the effects of the present invention. Here, B min is the lower limit of the proper intensity range of the magnetic flux density of the electromagnetic brake, the magnetic flux density is lower than the lower limit value, prevents the inclusions and bubbles from entering downward ride discharge flow not expired. Also, B max is the upper limit of the proper intensity range of the magnetic flux density of the electromagnetic brake, the magnetic flux density exceeds this upper limit value, since the increased flow along the immersion nozzle 2 becomes too strong, accordingly downdraft inverted becomes stronger, frequency of contact between the solidified shell 8 of inclusions and air bubbles carried by the downward flow increases. As a result, surface defects tend to occur. The B min and B max are defined by a combination of the factors influencing the flow in the mold.
[0029]
　Specifically, the mold having short sides and long sides in a horizontal cross-sectional shape, the long side ends, the mold thickness is measured as the distance between the opposite long sides in the mold (D 0 and), the horizontal cross section the mold having short sides and long sides, in the long side center, the maximum value of the mold thickness is measured as the distance between the opposite long sides in the mold (D max and) vertical from the molten steel surface to the center electromagnetic brake coil direction distance (H 0 and), the vertical distance from the immersion nozzle bottom surface to center the electromagnetic brake coil (H SEN and), the flow rate of the discharged from the immersion nozzle molten steel and (v), and a discharge angle of the molten steel (theta) by combining so as to satisfy the above equation (1), the first time, to reduce both the internal defect and surface defect of the mold, it is possible to increase the cleanliness of the slab.
[0030]
　H SEN as the value of decreases, the braking force to the discharge flow by the electromagnetic brake is increased, the lowering speed of the discharge flow is suppressed, the flow velocity of the upward flow as shown in FIGS. 3 and 4 becomes large. As a result, since the upward flow also increases the flow velocity of the downward flow formed by inverting near the surface of the molten steel, inclusions and bubbles carried by the descending flow, mold long sides walls 3a, on 3b coagulation probability of surface defects trapped in contact with the shell 8 becomes high.
[0031]
　On the other hand, H SEN the value of becomes large, H 0 becomes close to, in addition to the effect of electromagnetic brake fade, fluctuation of the molten steel surface is increased. As a result, likely to occur entrainment of mold powder.
[0032]
　Also, the larger the value of θ is large braking force by the electromagnetic brake is required, they tend to be upward flow increases.
[0033]
　Thus, increased or decreased for each variable in the above (Formula 1), in order to achieve different effects, respectively, conventionally, in a continuous casting machine constituted by combining them, each time changing the like mold size, the casting speed and the immersion nozzle to, determining the optimum intensity of the electromagnetic brake has been difficult. In contrast, according to the present invention, the the electromagnetic brake an appropriate strength according to (Equation 1), by an extremely simple method called, certainly reduce both the internal defect and surface defect of the mold, the slab it is possible to enhance the cleanliness.
[0034]
　In the present invention, mold, D max = D 0 if a rectangular mold is, the flow velocity v of the molten steel discharged from the immersion nozzle is preferably 0.685m / s ~ 0.799m / s. By the molten steel flow velocity v is 0.685m / s or more, it is easy to obtain a molten steel flow to suppress the capture of the solidification interface of the inclusions. Further, by the molten steel flow velocity v is less than 0.799m / s, it becomes easy to suppress the fluctuation of the molten steel surface.
[0035]
　On the other hand, in the present invention, when the mold is funnel mold, D max / D 0 is preferably 1.16 to 1.24. D max / D 0 by is 1.16 or more, upward flow is gradually formed across, it becomes easy to suppress the formation of the descending flow along the solidification interface. Also, D max / D 0 by is 1.24 or less, it becomes easy to reduce the resistance when removing the solidified shell from the mold. If the template is a funnel mold, from the viewpoint of conspicuous effect of the above, D max / D 0 is more preferably from 1.18 to 1.22.
[0036]
　Also, if the mold is a funnel mold, H SEN / H 0 is preferably 0.161 to 0.327. H SEN / H 0 by is 0.161 or more, it becomes easy to stabilize the heat supply to the molten steel surface. Also, H SEN / H 0 by is 0.327 or less, it becomes easy to suppress the fluctuation of the molten steel surface. If the template is a funnel mold, from the viewpoint of significantly the effect of the, H SEN / H 0 is more preferably 0.15-0.30.
[0037]
　Also, if the mold is a funnel mold, the flow velocity v of the molten steel discharged from the immersion nozzle is preferably 0.441m / s ~ 1.256m / s. By the molten steel flow velocity v is 0.441m / s or more, captured along with the molten steel flow is obtained to suppress the inclusion facilitates heat supply to the molten steel surface. Further, by the molten steel flow velocity v is less than 1.256m / s, it becomes easy to suppress the fluctuation of the molten steel surface. If the template is a funnel mold, from the viewpoint of conspicuous effect of the molten steel flow velocity v is more preferably 0.500m / s ~ 1.100m / s.
[0038]
　Also, if the mold is a funnel mold, the molten steel discharge angle θ of, it is preferably -45 ° ~ -5 °. By jetting angle of the molten steel θ is -45 ° or more, it is easy to heat supply to the molten steel surface. Further, by the jetting angle of the molten steel θ is -5 ° or less, it becomes easy to suppress the fluctuation of the molten steel surface. If the template is a funnel mold, from the viewpoint of conspicuous effect of the above, the molten steel discharge angle θ of, and more preferably -45 ° ~ -15 °.
Example
[0039]
　Perform continuous casting of steel in casting conditions of each condition shown in Table 1 to evaluate the quality of the manufactured coil. Quality Evaluation of coils, specifically, for each 50 or more coils, counting the sliver flaw by visual inspection, by its flaws number, ◎ (flaws number ≦ 0.5 pieces / coil), ○ (0. 5 pieces / coil gave the evaluation of 1.0 pieces / coil).
[0040]
[Table 1]

[0041]
　Example 1,2,4,5,6,7,8,9,11,13,14,15,18,20,21,23,24 is the electromagnetic brake flux density within a proper range and funnel it is obtained by using a mold. As shown in these examples, an electromagnetic brake flux density is within the appropriate range, and in the case of using a funnel mold, and other casting conditions (casting speed, casting width, thickness and immersion nozzle condition bulging of the funnel portion) without being affected by, both were confirmed to exhibit a very good ◎ coil quality.
[0042]
　Example 3, 26 are both but electromagnetic brake flux density is within the proper range, is obtained by using a free rectangular mold of the funnel section. Coil quality in these conditions was good ○.
Examples 10,17,19,27 are all, by using the funnel mold, and, while within the proper range electromagnetic brake magnetic flux density, an example in which the casting speed to be low. Coil quality in these conditions was both good ○.
Example 22 uses a funnel mold, and, while within the proper range electromagnetic brake magnetic flux density, is an example of the expedited casting speed. Coil quality in these conditions was good ○.
Example 25 uses a funnel mold, and, while within the proper range electromagnetic brake magnetic flux density, an example in which the ejection angle shallower (-5 °). Coil quality in these conditions was good ○.
[0043]
　Comparative Examples 1-10 are all those not in the electromagnetic brake magnetic flux density within a proper range. Coil quality in these conditions was any bad ×.
[0044]
　And Comparative Examples 7 and 8, Examples 12 to 16, unified other conditions other than the electromagnetic brake flux density, in the above example (equation 1) proper range of the electromagnetic brake flux density due to the 657 ~ 4795 (Gauss) is there.
Examples 13 to 15, the electromagnetic brake magnetic flux density, a proper range, which apart from any upper limit value and the lower limit value, both were confirmed to exhibit a very good ◎ coil quality.
Comparative Example 7, 24% less than the proper lower limit electromagnetic brake flux density, Comparative Example 8, the electromagnetic brake flux density was 4% greater than the appropriate upper limit. These are all the coil quality was poor ×.
Example Using the funnel mold 12, an electromagnetic brake flux density, although it is within the proper range, as compared with the electromagnetic brake flux density in Examples 13-15, an example in which a near lower limit. Coil quality in these conditions was good ○.
Example 16 Using the funnel mold, an electromagnetic brake flux density, although it is within the proper range, as compared with the electromagnetic brake flux density in Examples 13-15, an example in which the upper limit value close. Coil quality in these conditions was good ○.
DESCRIPTION OF SYMBOLS
[0045]
　1 ... mold
　2 ... immersion nozzle
　3, 3a, 3b ... long side wall
　4 ... electromagnetic brake device
　5 ... discharge port
　6 ... discharge flow
　7a, 7b ... short side wall
　8 ... solidified shell
　9 ... electromagnetic brake coil center

claims
[Claim 1]
　While applying an electromagnetic brake to the discharge flow discharged from the discharge hole of the immersion nozzle, a continuous casting method of steel supplying molten steel into the mold,
　a magnetic flux density of the electromagnetic brake (B), the following (Equation 1) continuous casting method of steel, characterized by a range.
B min ≦ B ≦ B max ... 　　　　　(Equation 1)
Here,

D 0 of the mold having short sides and long sides in = horizontal cross-sectional shape, the long sides opposite ends, is measured as the distance between the opposite long sides in the mold that the mold thickness (m), D
max = the mold having short sides and long sides in a horizontal cross-sectional shape, in long side center, the maximum value of the mold thickness is measured as the distance between the opposite long sides in the mold (m ), H
0 vertical distance from = the molten steel surface to the center electromagnetic brake coil (m), H
SEN vertical distance from = immersion nozzle bottom surface to the center electromagnetic brake coil (m), v =
the molten steel discharged from the immersion nozzle flow rate (m / s),
theta = discharge angle of molten steel (°).
[Claim 2]
　As the mold, characterized by using a rectangular mold having short sides and long sides in a horizontal cross-sectional shape, the continuous casting method of steel according to claim 1.
[Claim 3]
　Wherein the flow velocity v of the molten steel is 0.685m / s ~ 0.799m / s, the continuous casting method of steel according to claim 2.
[Claim 4]
　As the mold, and characterized in that having short sides and long sides in a horizontal cross-sectional shape, and the distance between the opposite long sides in a mold, using a funnel mold expanded than the long side ends in the long side center to, continuous casting method of steel according to claim 1.
[Claim 5]
　Wherein D max / D 0 is characterized in that it is a 1.16 to 1.24, the continuous casting method of steel according to claim 4.
[Claim 6]
　The H SEN / H 0 is characterized in that it is a 0.161 to 0.327, the continuous casting method of steel according to claim 4 or 5.
[Claim 7]
　Wherein the flow velocity v of the molten steel is 0.441m / s ~ 1.256m / s, the continuous casting method of steel according to any one of claims 4-6.
[8.]
　Wherein the discharge angle θ of the molten steel is -45 ° ~ -5 °, the continuous casting method of steel according to any one of claims 4-7.