JP4902276B2 - Continuous casting method of high carbon steel using dipping nozzle with dimple - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for continuously casting a high carbon steel, in which the delay of solidification is restrained and the excellent surface quality of a cast slab is obtained. <P>SOLUTION: The shape of spouting holes 2 in an immersion nozzle 100 used for continuous casting, is properly determined. For example, in a vertical cross sectional face (in the figure) of the immersion nozzle 100, the angle &theta;4 formed between a hole boring direction of the spouting holes 2 and a surface Src perpendicular to the axial line of the immersion nozzle 100, and the opening area of the spouting holes 2, are set in the prescribed ranges. A mold having the width and thickness properly set at the upper end part, is used, and further, a casting velocity Vc is 0.8-1.6 m/min and the over-heating degree &Delta;T is 20-45&deg;C. Furthermore, the continuous casting is performed while the molten steel poured into the mold is subjected to electromagnetic-stirring, wherein the electromagnetic strength in the mold M-EMS is set to 0-1000 gauss. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to a continuous casting method of high carbon steel having a carbon content C [wt%] of 0.20 to 0.60.

In the conventional immersion nozzle, for the purpose of suppressing the so-called splash phenomenon that the molten steel poured into the immersion nozzle at the start of casting is ejected so as to jump up by vigorously hitting the bottom surface (nozzle inner bottom surface), A discharge hole drilled in the lower part of the immersion nozzle is provided slightly above the bottom surface to form a so-called hot water reservoir.
However, when molten steel having a velocity gradient in the mold thickness direction is poured into the immersion nozzle, or when a velocity gradient in the mold thickness direction is generated in the molten steel poured into the immersion nozzle, the molten steel in the pool portion due to a pressure difference, the molten steel flow across the basin portion to the mold thickness direction occurs (see FIG. 6 (a)). The transverse molten steel flow (refer to FIG. 6 (b)) to induce a rotational flow with axis parallel to the mold width direction, as a result, the drift of the mold thickness direction of molten steel discharge flow from the discharge hole of the immersion nozzle It will occur.
Then, due to the drift of the molten steel discharge flow, the supply of heat to the meniscus of the molten steel in the mold becomes non-uniform, and the mold powder floating on the meniscus is not uniformly hatched, but the unhatched powder Scattered, the unhatched powder is caught between the solidified shell and the inner wall surface of the mold, and so-called vertical cracks are generated.
In addition, it has already been clarified that the drift of the molten steel discharge flow does not depend on the opening / closing direction of the slide plate for adjusting the flow rate of the molten steel poured into the immersion nozzle (Non-Patent Document 1 and Non-Patent Document 1). Patent Document 2).

  For the purpose of preventing the drift of the molten steel discharge flow in the mold thickness direction, for example, the inner wall of the immersion nozzle is formed in a mogul shape (uneven shape), and the molten steel flow in the immersion nozzle is used as a strong turbulent flow field. Technology has been proposed. However, according to the present technology, the manufacturing cost of the immersion nozzle is greatly increased, and the effect of making the molten steel flow a strong turbulent flow field is lost in a relatively short period of time due to deposits on the inner wall. It is supposed to end up.

In order to solve the above problems, the inventors of the present invention (Yoshida, Mimura), prior to the present application, drifted in the mold thickness direction of the molten steel discharge flow without disturbing the effect of suppressing the splash phenomenon at the start of casting. Has been invented a continuous casting immersion nozzle (Japanese Patent Application No. 2006-040933).
In short, the present invention provides a recess extending in the nozzle diameter direction on the inner bottom surface of the nozzle of the immersion nozzle, and variously limits the shape of the recess.

  Based on the above, the main object of the present invention is to provide a high carbon steel continuous casting method capable of improving the quality of the cast high carbon steel on the premise of using an immersion nozzle that exhibits this useful effect. Is to provide.

  As this type of technology, Patent Document 1 discloses a slab continuous casting method and an immersion nozzle. In the continuous casting method described in Patent Document 1, the relationship between the discharge flow rate of the nozzle, the mold long side width, and the discharge hole average width is appropriately set.

JP 2002-18562 A Kenji Ichikawa, 2 others, “About the flow in a submerged nozzle tube [Results of water model experiment on tundish SN; 3rd report]”, Refractory, Refractory Technology Association, January 1990, Vol. 42, No. 1 , P.43-46 A. R. ARManderas, “Dynamics of two-phase downwards flow in submerged entry nozzle and its influence on the two-phase flow in the mold ”, Int. J. International Journal of Multiphase Flow, Netherlands, ELSEVIER, 2005, Vol. 31, p.643-665

  However, according to the description of the Example of the above-mentioned Patent Document 1, an immersion nozzle having a completely different shape (particularly the inner bottom surface of the nozzle) is employed as compared with the immersion nozzle used when using the present invention. In the technical field to which the present invention belongs, the shape of the immersion nozzle is extremely important. In this sense, it can be said that the technical field to which the above-mentioned Patent Document 1 belongs and the technical field to which the present invention belongs are different.

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, continuous casting of high carbon steel having a carbon content C [wt%] of 0.20 to 0.60 is performed by the following method.
That is, a continuous casting immersion nozzle in which a pair of opposed discharge holes are perforated in the vicinity of the nozzle inner bottom surface, and a recess extending in the nozzle radial direction is formed in the nozzle inner bottom surface, An immersion nozzle having the following characteristics is used.
-The vertical cross section of the said recessed part in the longitudinal direction is a rectangle or a trapezoid.
The side of the vertical cross section of the concave portion in the longitudinal direction is parallel to the longitudinal direction of the immersion nozzle or is inclined more than 0 degree and less than 50 degrees with respect to the longitudinal direction of the immersion nozzle .
-The said recessed part is an internal angle of the vertical cross section of the longitudinal direction, Comprising: The thing of the side far from a nozzle inner bottom face is formed so that it may be 90 degree | times or more and 140 degrees or less.
H / D, which is the ratio of the depth h of the vertical cross section in the longitudinal direction of the recess to the inner diameter D of the immersion nozzle, is in the range of 0.1 ≦ h / D ≦ 1.0.
Y / Y, which is a ratio of the width y of the lower side of the vertical section of the concave portion in the longitudinal direction and the opening width Y of the inner circumferential side opening end of the discharge hole, is 0.4 ≦ y / Y ≦ 1. It is in the range of 0.
And direction toward said discharge port is a direction connecting the opening center of the center point and the discharge hole of the nozzle inner diameter in a plan view, a longitudinal direction of the recess, the angle θ2 formed by the the direction of the discharge hole, Θ2 / θ3, which is the ratio of the angle θ3 formed by the surface connecting the side of the inner circumferential opening end of the discharge hole and the axis of the immersion nozzle, is 0 ≦ θ2 / θ3 ≦ 1.0. Within range.
-Opening area Na [cm < ² >] of the inner peripheral side opening end of the said discharge hole is 35-115.
- the axis of said immersion nozzle, perpendicular to the person and direction of discharge hole, and the contour line of the front end side of the immersion nozzle of the contour of the discharge holes appearing in the pair in the cross section including the axis of said immersion nozzle The angle θ4 [deg.] Formed by the surface is −5 to 55.
Also, a mold for cooling molten steel to form a solidified shell having a predetermined shape, which has the following characteristics, is used.
The mold width W [mm] at the upper end of the mold is 800-2100.
The mold thickness P [mm] at the upper end of the mold is 200 to 320.
Further, the casting speed Vc [m / min] is set to 0.8 to 1.6, and the degree of superheat ΔT [° C.] is set to 20 to 45.
Additionally, the mold in the electromagnetic stirring intensity M-EMS [gauss] to continuous casting and 0-1000.
The above-mentioned electromagnetic stirring strength M-EMS [gauss] in the mold is the center in the width direction of the mold, is separated from the upper end of the mold by 250 mm toward the lower end, and from the inner surface on the wide surface side of the mold. A value measured by an appropriate gauss meter at a point 15 mm away (the unit is [gauss]).

  According to this, without disturbing the effect of suppressing the splash phenomenon at the start of casting, the drift in the mold thickness direction of the molten steel discharge flow is reduced, the so-called solidification delay is reduced, and high-quality high-carbon steel. Can be continuously cast.

First, regarding the immersion nozzle disclosed in the prior application (Japanese Patent Application No. 2006-040933, etc.) relating to the above-mentioned immersion nozzle invented by the inventors of the present invention (Yoshida, Mimura), the configuration and The excellent effects (including multiple tests conducted to confirm the technical effects) will be described in detail.
The immersion nozzle is, for example, used in a continuous casting machine as a guide for smoothly pouring molten steel temporarily stored in a tundish (not shown) into a mold for forming a slab shell. It is.

FIG. 1 is a longitudinal sectional view of an immersion nozzle according to an embodiment of the present invention, and FIG. 2 is a sectional view taken along line 2-2 in FIG. 3 is an enlarged view of portion A in FIG. 1, and FIG. 4 is a cross-sectional view taken along line 4-4 in FIG. FIG. 5 is a view similar to FIG.

  In this embodiment, a continuous casting immersion nozzle (hereinafter simply referred to as an immersion nozzle) 100 is formed in a substantially cylindrical shape with a bottom as shown in FIGS. A pair of opposed discharge holes 2 and 2 are perforated in the vicinity of the bottom surface 1 (see also FIG. 4). In the present embodiment, as shown in FIG. 1, the discharge holes 2 and 2 are formed so that the vertical cross section in the drilling direction is substantially rectangular.

As shown in FIG. 2, the discharge holes 2 and 2 are formed so as to expand in a fan shape with increasing distance from the axis of the immersion nozzle 100, and are formed slightly obliquely downward as shown in FIG.
Further, in the present embodiment, the immersion nozzle 100 is configured such that the lower side of the inner peripheral side opening ends 2a and 2a of the discharge holes 2 and 2 and the nozzle inner bottom surface 1 are the axis of the immersion nozzle 100 as shown in FIG. It is comprised so that it may correspond in a direction.

  As shown in FIGS. 1 to 4, etc., the nozzle inner bottom surface 1 extends in the diameter direction (nozzle radial direction) of the immersion nozzle 100 and has a longitudinal length (see FIGS. 2 and 4). A recess 4 that substantially matches the inner diameter D of the immersion nozzle 100 is provided.

The vertical section of the concave portion 4 in the longitudinal direction is formed in a rectangular or trapezoidal shape as shown in FIGS. 1 and 3 (in this embodiment, a substantially trapezoidal shape as shown). The “rectangular shape or trapezoidal shape” includes those in which arcs are formed at the corners as shown in FIGS. 1 and 3.

As shown in FIG. 3, the side 4a of the vertical section of the concave portion 4 in the longitudinal direction is parallel to the longitudinal direction of the immersion nozzle 100 (that is, the vertical direction) or 0 degrees with respect to the longitudinal direction of the immersion nozzle 100. And is inclined to the outside by 50 degrees or less. In other words, when the outer side inclination angle θ1 of the side edge 4a is not less than 0 degrees and not more than 50 degrees and the outer side inclination angle θ1 is 0 degree (the side edge 4a in the vertical section of the longitudinal direction of the recess 4 is In the case of being parallel to the longitudinal direction of the immersion nozzle 100) , it can be said that the vertical cross section of the concave portion 4 is rectangular. In other words, the recess 4 is formed so that the inner corner of the vertical cross section in the longitudinal direction and the far side with respect to the nozzle inner bottom surface 1 is 90 degrees or more and 140 degrees or less.

  Further, as shown in the figure, h / D which is a ratio of the depth h of the vertical cross section in the longitudinal direction of the recess 4 and the inner diameter D of the immersion nozzle 100 is 0.1 ≦ h / D ≦ 1. It is comprised so that it may become in the range of 0. In the case of this figure, the ratio h / D is about 0.39.

  Further, as shown in this figure, y / is the ratio of the width y of the lower side of the vertical section of the recess 4 in the longitudinal direction and the opening width Y of the inner peripheral side opening ends 2a and 2a of the discharge holes 2 and 2. Y is configured to be within a range of 0.4 ≦ y / Y ≦ 1.0. In the figure, the ratio y / Y is about 0.3.

In the present embodiment, as shown in the figure, an arc having a radius R1 within the range of 0 ≦ R1 ≦ y / 2 may be formed at the corner of the vertical section of the recess 4 in the longitudinal direction. . For example, the lower side of the vertical cross section in the longitudinal direction of the concave portion 4 may be a complete arc without a flat portion (in this case, R1 is about y / 2). In the present embodiment, the radius R1 is about y / 3 as shown in FIG.
Note that, as described above, the symbol y is the width of the lower side of the vertical section of the recess 4 in the longitudinal direction. However, when the corner of the vertical section is formed in an arc shape as shown in FIG. Let y be considered as the distance between the first virtual intersection of the lower side and the one side 4a and the second virtual intersection of the lower side and the other side 4a.

For example, as shown in FIG. 5, when the immersion nozzle 100 is viewed in a cross section perpendicular to the axial direction, the center point of the inner diameter of the immersion nozzle 100 and the opening center of the discharge holes 2 and 2 are connected in a plan view. direction towards the discharge hole 2, 2 is a direction (direction of the center serving line hole extends), a longitudinal direction of the recess 4, the angle θ2 formed by the direction toward said discharge port 2.2 .Theta.2 / .theta.3, which is the ratio of the angle .theta.3 formed by the surface connecting the sides of the inner peripheral opening ends 2a and 2a of the discharge holes 2 and 2 and the axis of the immersion nozzle 100, is 0.ltoreq. The configuration is such that θ2 / θ3 ≦ 1.0. In the present embodiment, the ratio θ2 / θ3 is substantially zero as shown in FIG.

Hereinafter, the molten steel flow in the immersion nozzle 100 according to the present embodiment will be described in comparison with a comparative example. FIG. 6 is a longitudinal sectional view of a conventional immersion nozzle, schematically showing a molten steel flow in the nozzle, and FIG. 7 is a view similar to FIG. Similarly, the molten steel flow in the nozzle is schematically represented. 6 and 7 , for convenience of explanation, the outer peripheral side opening end of the discharge hole that appears inside the inner peripheral side opening end in the drawing is omitted.

In the conventional immersion nozzle as shown in FIG. 6 (a), when molten steel having a velocity gradient in the mold thickness direction is poured, or when a velocity gradient in the mold thickness direction is generated in the molten steel for some reason, Due to the pressure difference of the molten steel generated in the hot water pool portion, a molten steel flow that crosses the hot water pool portion in the mold thickness direction is generated. Then, as shown in FIG. 6 (b), this transverse molten steel flow induces a rotating flow having an axis parallel to the mold width direction, and as a result, the molten steel discharge flow from the discharge hole of the immersion nozzle has a mold thickness direction. Drift will occur.
On the other hand, as shown in FIG. 7 , the immersion nozzle 100 according to the present embodiment is not formed with a hot water reservoir as in the comparative example, and instead, the nozzle inner bottom surface 1 is radially arranged as described above. A recess 4 extending in the shape of the recess 4 is provided with a width (y) smaller than at least the opening width Y of the inner peripheral opening ends 2a and 2a of the discharge holes 2 and 2 (also in FIG. 3). See also). Therefore, even if molten steel having a velocity gradient in the mold thickness direction is poured, or even if a molten steel having a velocity gradient in the mold thickness direction is generated in the molten steel for some reason, the rotational flow is induced. The crossed molten steel flow is very difficult to generate, and the molten steel discharge flow is discharged in the form of the discharge holes 2 and 2 in the drilling direction. Thereby, compared with the said conventional immersion nozzle, the immersion nozzle 100 which concerns on this embodiment can reduce significantly the drift of the mold thickness direction of a molten steel discharge flow. In addition, the concave portion 4 is appropriately provided in the inner bottom surface 1 of the nozzle so that the splash phenomenon at the start of casting described above can be suppressed.

  Hereinafter, a test for confirming the technical effect of the immersion nozzle 100 according to the present embodiment, that is, a confirmation test for evaluating the drift in the mold thickness direction and the splash phenomenon of the molten steel discharge flow will be described. Each numerical range described above is reasonably supported by the following confirmation test.

  In this test, as shown in Table 1 below, various recesses with different shapes and sizes were provided on the bottom surface inside the nozzle, and a discharge experiment using water instead of molten steel was conducted. The drift and splash phenomenon were evaluated, and the shape and size of the recesses were comprehensively evaluated based on these evaluations.

(Evaluation of drift)
The evaluation of “drift” in Table 1 is specifically performed as follows. FIG. 8 is a front view of the immersion nozzle.
That is, as shown in FIG. 8 , the flow rate of the water flow discharged from the discharge hole of the submerged nozzle was measured at 9 points in a checkerboard shape using an appropriate flow rate detection device (for example, an electromagnetic current meter). An example of the measurement results shown in FIGS.
And among the measurement results, the speed difference between the lower right column and the lower left column is calculated (see the thick circle in FIG. 8 ), and the absolute value of the speed difference is less than 0.2 m / s. (No drift in the mold thickness direction) ”, and when it was 0.2 m / s or more, it was evaluated as“ × (with drift in the mold thickness direction) ”.
Note that the measurement point as the lower right column is specifically a point that is 10 mm away from one side and the lower side of the outer peripheral opening end of the discharge holes 2 and 2. Similarly, the measurement point as the lower left column is specifically a point that is 10 mm away from the other side and lower side of the outer peripheral opening end of the discharge holes 2 and 2.
In this evaluation, the total discharge amount of water from the discharge hole of the immersion nozzle was 550 [L / min].

(Evaluation of splash phenomenon)
By the way, as described above, the “splash phenomenon” refers to a phenomenon in which the molten steel poured into the immersion nozzle at the start of casting is discharged so as to jump up by vigorously hitting the bottom surface. Not limited to this, the molten steel is ejected vigorously downwardly from the discharge hole of the immersion nozzle, and the molten steel jumps up sequentially through the upper end surface of the dummy bar and the narrow surface of the mold that are inserted in the mold in advance at the start of casting. It also includes the phenomenon that would
The “scattering height” in Table 1 relates to the former phenomenon, and the “bubble dive depth” in Table 1 also relates to the latter phenomenon. The latter phenomenon was indirectly evaluated by evaluating the strength of the water flow discharged downward from the discharge hole (bubble dive depth). Note that these splash phenomena are not preferable because of a decrease in productivity.

The evaluation of the “scattering height” in Table 1 was specifically performed as follows. FIG. 11 is a side view of the immersion nozzle.
That is, as shown in this figure, the arrival height of water droplets scattered upward from the discharge hole of the immersion nozzle is measured visually with reference to the upper side of the outer peripheral opening end of the discharge hole, and the arrival height is determined. The flying height.
Then, when the scattering height was less than 15 cm, it was evaluated as “◯ (small scattering height)”, and when it was 15 cm or more, it was evaluated as “× (large scattering height)”.
At this time, the discharge amount of water from the discharge hole of the immersion nozzle was set to 800 [L / min].

Specifically, the evaluation of “bubble dive depth” in Table 1 was performed as follows.
That is, as shown in this figure, below the immersion nozzle, a water tank whose water surface height is adjusted so that the vertical distance to the lower end of the immersion nozzle is 5 cm is installed, and downward from the discharge hole of the immersion nozzle. The arrival depth of the bubbles in which the water stream ejected vigorously was taken in was measured visually with reference to the water surface.
And when this reach | attainment depth was less than 35 cm, it was set as "(circle) (bubble dive depth small)", and when it was 35 cm or more similarly, it evaluated as "* (bubble dive depth is large)."
In addition, the observation object at the time of measuring this reach | attainment depth was limited to the diameter of 5 mm or more among the bubbles entrained by the water flow.
Also at this time, the discharge amount of water from the discharge hole of the immersion nozzle was similarly set to 800 [L / min].

  The “comprehensive evaluation” in Table 1 above is based on whether or not all the evaluations regarding the “drift”, “scattering height”, and “bubble dive depth” are good (that is, “◯”). Is to be judged.

According to this Table 1, if the immersion nozzle 100 for continuous casting constituted as follows is used, the drift in the mold thickness direction of the molten steel discharge flow is greatly reduced without hindering the effect of suppressing the splash phenomenon at the start of casting. It can be seen that it can be reduced.
-The vertical cross section of the said recessed part 4 in the longitudinal direction is a rectangle or a trapezoid.
The side 4a of the vertical cross section in the longitudinal direction of the recess 4 is parallel to the longitudinal direction of the immersion nozzle 100 or is inclined more than 0 degree and less than 50 degrees outside with respect to the longitudinal direction of the immersion nozzle 100. Yes.
The concave portion 4 is formed so that an inner angle of a vertical cross section in the longitudinal direction thereof is 90 ° or more and 140 ° or less on a side far from the nozzle inner bottom surface 1.
H / D, which is the ratio of the depth h of the vertical section in the longitudinal direction of the recess 4 to the inner diameter D of the immersion nozzle, is in the range of 0.1 ≦ h / D ≦ 1.0.
Y / Y, which is the ratio of the width y of the lower side of the vertical cross section of the recess 4 in the longitudinal direction and the opening width Y of the inner peripheral opening ends 2a and 2a of the discharge holes 2 and 2, is 0.4. ≦ y / Y ≦ 1.0.
· A direction towards the discharge hole 2, 2 is a direction connecting the opening center of the center point and the discharge hole 2.2 of the nozzle inner diameter in a plan view, a longitudinal direction of the recess 4, the angle θ2 formed by the and direction towards the discharge hole 2, 2, a surface connecting the axial center of the discharge holes 2.2 on the inner peripheral side opening end 2a-2a the immersion nozzle 100 and the sides of the angle θ3 formed by the ratio of Θ2 / θ3 is in the range of 0 ≦ θ2 / θ3 ≦ 1.0.

  Next, an embodiment of the high carbon steel continuous casting method according to the present invention, which is performed using the above immersion nozzle, will be described in detail. In addition, the steel type which this invention makes the casting object is high carbon steel whose carbon content C [wt%] is 0.20-0.60.

In the present embodiment, the immersion nozzle 100 is further configured as follows as shown in FIGS. 12 and 13 (with the following structural limitations). FIG. 12 is a view similar to FIG. FIG. 13 is a view similar to FIG. For convenience of explanation, in FIG. 12 , the opening end on the outer peripheral side of the discharge hole 2 is omitted.

That is, in this embodiment, as shown in FIG. 12 , the opening area Na [cm ² ] of the inner peripheral side opening end 2 a of the discharge hole 2 is set to 35 to 115.
Strictly speaking, considering that the inner peripheral side wall surface of the immersion nozzle 100 is annular, that is, a curved surface, the opening area Na is considered as follows. That is, it is assumed that the area with the opening area Na surrounded by the inner peripheral side opening end 2a which is projected onto the plane of FIG. 12. In short, the opening area Na is obtained based only on the longitudinal sectional view without considering the fact that the inner circumferential side opening end 2a appears on the curved surface. In this respect, the opening area Na can also be referred to as a cross-sectional area in the vicinity of the inner peripheral side opening end 2a of the discharge hole 2.

Further, in the present embodiment, as shown in FIG. 13 , an angle θ4 [deg] formed by the perforating direction of the discharge holes 2 and 2 and the surface Src perpendicular to the axis of the immersion nozzle 100 is set to −5 to 55. More specifically, it is as follows.
That is, FIG. 13, the axis of the immersion nozzle 100 is a longitudinal sectional view of the immersion nozzle 100 including a the direction of the discharge hole, the inside cross-section at the same time. In the cross section of this drawing, a pair of outlines of the discharge holes 2 appear for one discharge hole 2. Then, out of the contour lines of the discharge holes 2 that appear in a pair in FIG. 13 , the contour line 2r on the tip side (lower side in the figure) of the immersion nozzle 100, a surface Src perpendicular to the axis line of the immersion nozzle 100, Is set to -5 to 55. (Note that even if the discharge hole 2 is formed in a circular shape or the like instead of a substantially rectangular cross section as will be described later, of course, the outline 2r can be easily conceived.)

Further, the mold 200 for forming a solidified shell having a predetermined shape and cooling the molten steel is poured from the immersion nozzle 100 is constructed as follows as shown in FIG. 14 in the present embodiment. FIG. 14 is a view showing the cross section of the immersion nozzle shown in FIG. 2 together with the mold into which the immersion nozzle 100 is inserted. In other words, in this drawing, the upper end surface of the mold and the cross section of the immersion nozzle are displayed at the same time.

That is, as shown in FIG. 14 , in this embodiment, the mold width W [mm] at the upper end of the mold 200 is set to 800-2100.
Similarly, the mold thickness P [mm] at the upper end of the mold 200 is set to 200 to 320.

In the continuous casting method of high carbon steel in the present embodiment, the casting speed Vc [m / min] is 0.8 to 1.6, and the degree of superheat (so-called superheat) ΔT [° C.] during continuous casting is 20 to. 45.
Note that the degree of superheat ΔT here is obtained as follows. That is, the molten steel temperature just before flowing into the immersion nozzle 100 connected in communication with the bottom surface of the tundish is measured using, for example, a thermocouple, and the measurement result Based on the above, the degree of superheat ΔT is calculated.

Further, in the present embodiment, the casting-mold electromagnetic stirring intensity M-EMS [gauss] of 0 to 1000. Specifically, it is as follows.
That is, a predetermined electromagnetic stirrer (such as a coil) is provided in the mold 200 as a pair so as to sandwich the immersion nozzle 100 in the mold thickness direction, for example. Then, due to the action of the electromagnetic stirring device, the molten steel in the mold 200 is clockwise or counterclockwise around the immersion nozzle 100 when viewed in a plane perpendicular to the axis of the immersion nozzle 100 (that is, in FIG. 14 ). It is configured to turn gently around.
The in-mold electromagnetic stirring intensity M-EMS [gauss] is the center in the width direction of the mold 200, separated by 250 mm toward the lower end with respect to the upper end of the mold 200, and on the wide surface side of the mold 200. It is a value (unit: [gauss]) measured by an appropriate gauss meter at a point 15 mm away from the inner wall surface.
In addition, as described above, electromagnetic stirring with the in-mold electromagnetic stirring strength M-EMS [gauss] set to 0 may be performed. Of course, this means that no electromagnetic stirring is required. That is, whether or not to perform electromagnetic stirring is arbitrary.

  More specifically, the high carbon steel continuous casting method described above is carried out as follows.

That is, the immersion nozzle 100 is detachably attached to the tundish tank bottom in advance before starting casting, and is attached so that the discharge holes 2 and 2 substantially face the narrow surface of the mold 200.
Next, when the tundish to which the immersion nozzle 100 is attached is lowered to a predetermined position, the tip (lower end) of the immersion nozzle 100 is inserted into the mold 200 to an appropriate depth.
Next, a dummy bar for pulling out the slab is inserted into the continuous casting machine.
Then, a slide valve provided at the bottom of the tundish is appropriately opened, so that the molten steel held in the tundish starts to be poured into the mold 200 through the immersion nozzle 100.
Next, the slab (solidified shell) formed by cooling in the mold 200 is drawn out to the dummy bar at a casting speed within the above-mentioned range. Thereby, continuous casting is started.

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

  First, a plurality of evaluation items of each confirmation test will be described. That is, (1) to (3) of (1) degree of solidification delay, (2) surface defect after rolling, and (3) slab quality.

(1) Degree of solidification delay Hereinafter, the degree of solidification delay as one of the evaluation items will be described. FIG. 15 is an explanatory diagram relating to the degree of solidification delay.
The “coagulation delay” is obtained by measuring as follows. That is, as shown in FIG. 15 , first, the cast slab is cut in a direction perpendicular to the longitudinal direction. Second, the distance between the white wire pattern (white band) appearing in the vertical section and the slab wide surface is measured. More specifically, the above-mentioned distance at two locations, that is, a location 5 cm away from the slab narrow surface along the slab wide surface and a location where the white wire bath pattern appears closest to the slab wide surface. Measure. In the figure, the distance measured at the former location corresponds to symbol A, and the distance measured at the latter location corresponds to symbol B. Third, by subtracting the distance B from the distance A and dividing the distance A by the distance A, the “coagulation delay” is obtained.
Here, the results of other tests conducted by the inventors of the present invention will be introduced. FIG. 16 is a diagram showing another test result regarding the degree of solidification delay. In the graph shown in this figure, the horizontal axis indicates the amount of narrow surface taper (in short, the extent to which the inner wall surface (narrow surface) of the mold becomes narrower as it advances in the casting direction), and the vertical axis indicates the solidification delay. Shows the degree. Each of the plurality of plots in this graph corresponds to the result of the test conducted multiple times for each narrow surface taper amount, and the white plot shows that no breakout occurred under the test conditions. The filled plot represents that a breakout has occurred under the test conditions. According to this graph, it can be said that the degree of solidification delay should be suppressed to at least 40% from the viewpoint of avoiding the occurrence of breakout.
Therefore, the degree of solidification delay was determined as described above, and when the value was 40% or less, it was evaluated as good.

(2) Surface Flaw after Rolling Hereinafter, the surface flaw after rolling as one of the evaluation items will be described.
The above-mentioned “surface defect after rolling” relates to the degree and presence of the defect grasped by observing the surface of the rolled slab at the stage after rolling the cast slab. In other words, when bubbles or inclusions are mixed in the molten steel when the molten steel is solidified or mold powder is mixed, when the cast slab is rolled, these impurities are rolled. It appears as linear wrinkles (so-called sliver wrinkles) on the surface of the piece.
Therefore, the surface of the rolled slab was observed in units of 1000 m in the longitudinal direction, and each test was evaluated according to the number of slivers observed at that time.
Specifically, when three or more slivers were found in the above observation, an evaluation of “x” was given, and when no sliver was found, an evaluation of “◯” was given.

(3) Slab quality Slab quality as one of the evaluation items is explained below.
This “slab quality” is for evaluating the presence or absence of a slab surface split (hereinafter referred to as a vertical split) that occurs along the casting direction on the slab surface. It is thought to be caused by the cause of. That is, the reason for the excessive solidification delay, the reason for the stress generated on the slab surface as a result of the non-uniform surface temperature of the slab, and the supply of heat to the meniscus. The reason is that the powder that was not hatched because of the excessively small was caught between the solidified shell and the mold.
Then, the surface of the slab after casting is observed, and when the vertical division is observed, the evaluation of the test condition is “vertical division (that is, with vertical division)”, and when the vertical division is not observed at all The evaluation of the test conditions was “◯”.

Next, test conditions and test results of each confirmation test will be described with reference to a table as appropriate.
<Test 1: Opening area of the inner circumferential side opening end of the discharge hole>
In this test, as shown in Table 2 below, attention is paid to the opening area Na of the inner peripheral side opening ends 2a and 2a of the discharge holes 2 and 2 of the immersion nozzle 100.

Other test conditions not described in Table 2 are as follows.
--------------------
D = 85 [mm]
h = 25 [mm], y = 40 [mm], Y = 70 [mm]
θ1 = 10 [deg.], θ2 = 0 [deg.], θ3 = 55 [deg.], R1 = 2 [mm]
h / D = 0.29, y / Y = 0.57, θ2 / θ3 = 0
--------------------
θ4 = 35 [deg.]
W = 1240 [mm], P = 240 [mm]
Vc = 1.0 [m / min], M-EMS = 550 [gauss]
--------------------

As shown in Table 2 above, in a test using an immersion nozzle with an opening area Na [cm ² ] of less than 35, the degree of solidification delay exceeded 40%. This is thought to be due to the following reasons.
That is, in order to ensure a predetermined casting speed, the discharge flow rate from the immersion nozzle of molten steel must be ensured appropriately. Therefore, when the opening area Na of the discharge hole of the immersion nozzle is smaller than that of the discharge nozzle, the discharge flow rate from the immersion nozzle of the molten steel becomes relatively large. As a result, it is considered that heat is excessively supplied to, for example, the corners of the solidified shell in the forming process in the mold, and the solidification delay is promoted.

On the other hand, in the test using an immersion nozzle with an opening area Na [cm ² ] exceeding 115, it was good in terms of the degree of solidification delay, but the evaluation on surface defects after rolling was not good, and regarding the slab quality However, good evaluation could not be obtained.
The reason why good evaluation of the surface defects after rolling was not obtained is considered to be as follows. That is, generally, the molten steel in the vicinity of the meniscus needs to have an appropriate flow rate to avoid air bubbles, inclusions such as CaO and Al ₂ O ₃ from staying (this is generally called a cleaning effect) ) However, when the opening area Na of the discharge hole of the immersion nozzle is larger than that of the immersion nozzle, the discharge flow rate from the immersion nozzle of the molten steel becomes relatively small, so-called inversion formed by the discharge flow from the immersion nozzle of the molten steel. The flow is not sufficiently secured, so the flow is lost to the molten steel near the meniscus, and as a result, the molten steel near the meniscus eventually solidifies in a state of containing bubbles and inclusions. .
The reason why the slab quality was not evaluated well is considered to be as follows. That is, since the reversal flow is not sufficiently ensured, the supply of heat to the meniscus becomes too small, and the powder suspended on the meniscus is not sufficiently hatched, so that the scattered undissolved powder This is probably because the powdered powder was caught between the solidified shell and the mold.

<Test 2: Angle>
In this test, as shown in Table 3 below, attention is paid to the angle θ4 formed by the perforation direction of the discharge holes 2 and 2 and the surface Src perpendicular to the axis of the immersion nozzle 100.

Other test conditions not described in Table 3 are as follows.
--------------------
D = 85 [mm]
h = 25 [mm], y = 40 [mm], Y = 65 [mm]
θ1 = 10 [deg.], θ2 = 0 [deg.], θ3 = 50 [deg.], R1 = 2 [mm]
h / D = 0.29, y / Y = 0.62, θ2 / θ3 = 0
--------------------
Na = 60 [cm ² ]
W = 1240 [mm], P = 240 [mm]
Vc = 0.9 [m / min], M-EMS = 550 [gauss]
--------------------

As shown in Table 3 above, surface flaws after rolling were observed in a test using an immersion nozzle having an angle θ4 [deg.] Less than −5. This is thought to be due to the following reasons.
That is, since the discharge direction of the discharge flow of the molten steel from the immersion nozzle is just upward, the above reversal flow, which plays an important role in giving a flow velocity and supplying heat to the molten steel near the meniscus, becomes excessive. I have. As a result, an excessive flow velocity was added to the molten steel in the vicinity of the meniscus. This is considered to be because the meniscus was swollen and the mold powder suspended on the meniscus was caught in the molten steel.

By the way, if it is a normal engineer in the field to which the continuous casting of high carbon steel belongs, it is generally difficult to consider the case where the angle θ4 [deg.] Is set to exceed 55. However, in order to fully examine the technical effect of the above-mentioned continuous casting method of high carbon steel, as shown in Table 3, a test using an immersion nozzle with θ4 [deg.] Of 60 is shown in Table 3. Also tried. In this case, the evaluation regarding the slab quality was not good. This is thought to be due to the following reasons.
That is, since the discharge direction of the discharge flow of the molten steel from the immersion nozzle was set to be obliquely downward (the molten steel discharged from the discharge hole collided with the mold narrow surface, the flow direction was changed upward) , Rising toward the meniscus, and eventually disappearing while changing the flow direction toward the immersion nozzle) The above reversal flow is difficult to be formed, the supply of heat to the meniscus becomes too small, and it floats on the meniscus This is probably because the powder was not sufficiently hatched, and the scattered unhatched powder was caught between the solidified shell and the mold.
Moreover, as shown in Table 3, the evaluation regarding the splash phenomenon was not preferable. However, this is because the angle θ4 [deg.] Is intentionally set to an angle that cannot be generally set as described above, and is not particularly alarming. In general, the approximate upper limit of the angle θ4 [deg.] Is about 45. In rare cases, an immersion nozzle having an angle θ4 [deg.] Set to 45 or more is used.

<Test 3: Mold width>
In this test, as shown in Table 4 below, the mold width W was noted.

Other test conditions not described in Table 4 are as follows.
--------------------
D = 85 [mm]
h = 25 [mm], y = 40 [mm], Y = 70 [mm]
θ1 = 10 [deg.], θ2 = 0 [deg.], θ3 = 55 [deg.], R1 = 2 [mm]
h / D = 0.29, y / Y = 0.57, θ2 / θ3 = 0
--------------------
Na = 50 [cm ² ], θ4 = 35 [deg.]
P = 240 [mm]
Vc = 1.0 [m / min], M-EMS = 550 [gauss]
--------------------

As shown in Table 4 above, in the test using a mold having a mold width W [mm] less than 800, the solidification delay exceeded 40%. This is thought to be due to the following reasons.
That is, in general, the extremely high temperature molten steel discharged from the immersion nozzle as described above requires some time to reach the narrow surface of the solidified shell formed in the mold, and therefore the molten steel is slightly cooled. After that, it reaches the narrow surface of the solidified shell. In this regard, when a mold having an excessively small mold width W is used as in this test, the molten steel reaches the narrow surface of the solidified shell formed in the mold before it is sufficiently cooled, that is, the solidified shell. It is considered that excessive heat was supplied to the surface, and as a result, the delay in solidification was promoted.

On the other hand, in the test using a mold having a mold width W [mm] exceeding 2100, the evaluation regarding the slab quality was not good. This is thought to be due to the following reasons.
That is, in general, the mold powder suspended on the meniscus flows between the solidified shell formed in the mold and the inner wall surface of the mold so that the heat removal characteristics of the mold with respect to the solidified shell are controlled. It has become. Nevertheless, if a mold with an excessive mold width W is used as in this test, the amount of mold powder inflow in the mold width direction (that is, the thickness of the mold powder, in other words, the amount of control of heat removal characteristics) is uneven. Will come out. This is considered to be because temperature unevenness occurs in the solidified shell in the width direction of the mold, and stress due to the temperature unevenness occurs in the solidified shell. This problem occurs not only in the width direction of the mold but also in the thickness direction at the same time.

<Test 4: Mold thickness>
In this test, as shown in Table 5 below, the mold thickness P was noted.

Other test conditions not described in Table 5 are as follows.
--------------------
D = 80 [mm]
h = 25 [mm], y = 40 [mm], Y = 65 [mm]
θ1 = 10 [deg.], θ2 = 0 [deg.], θ3 = 54 [deg.], R1 = 2 [mm]
h / D = 0.31, y / Y = 0.62, θ2 / θ3 = 0
--------------------
Na = 60 [cm ² ], θ4 = 45 [deg.]
W = 1240 [mm]
Vc = 1.0 [m / min], M-EMS = 550 [gauss]
--------------------

As shown in Table 5 above, surface defects after rolling were observed in a test using a mold having a mold thickness P [mm] of less than 200. This is thought to be due to the following reasons.
That is, since the mold thickness P was smaller than that of the mold, the gap between the immersion nozzle and the wide-surface mold inner wall surface was narrowed. For this reason, the gap (flow path) between the immersion nozzle and the inner wall surface of the mold on the wide surface side is generated in spite of the fact that the reverse flow is generated in order to achieve the above-described cleaning effect on the molten steel around the immersion nozzle. ) is narrow, very hitch molten steel flow in the gap, as a result, is considered gills and because he could not exert sufficient cleaning effect on the molten steel in the gap between the immersion nozzle and the broad surface side in the mold wall .

On the other hand, in the test using a mold having a mold thickness P [mm] exceeding 320, the evaluation regarding the slab quality was not good. This can be explained in substantially the same manner as the above-described test using a mold having a mold width W [mm] exceeding 2100, and is summarized as follows.
That is, it is considered that the unevenness in the inflow amount of the mold powder in the thickness direction of the mold causes the temperature unevenness in the solidified shell in the thickness direction, and stress is generated due to the temperature unevenness. This problem occurs not only in the thickness direction of the mold but also in the width direction.

<Test 5: Casting speed>
In this test, as shown in Table 6 below, attention was paid to the casting speed.

Other test conditions not described in Table 6 are as follows.
--------------------
D = 85 [mm]
h = 25 [mm], y = 40 [mm], Y = 70 [mm]
θ1 = 10 [deg.], θ2 = 0 [deg.], θ3 = 55 [deg.], R1 = 2 [mm]
h / D = 0.29, y / Y = 0.57, θ2 / θ3 = 0
--------------------
Na = 60 [cm ² ], θ4 = 45 [deg.]
W = 1240 [mm], P = 240 [mm]
M-EMS = 500 [gauss]
--------------------

As shown in Table 6 above, in the test in which the casting speed Vc [m / min] was set not to satisfy 0.8, the evaluation regarding the slab quality was not good. This is thought to be due to the following reasons.
That is to say, the fact that the casting speed is relatively low means that the discharge amount of molten steel from the immersion nozzle is relatively small. In short, since the discharge speed of the molten steel from the immersion nozzle is relatively small, the aforementioned reverse flow formed by the discharge flow of the molten steel is not sufficiently formed, and the supply of heat to the meniscus is too small. Therefore, it is considered that the powder unflooded on the meniscus was not sufficiently hatched, and the scattered unhatched powder was caught between the solidified shell and the mold.

On the other hand, in the test in which the casting speed Vc [m / min] was set to exceed 1.6, the degree of solidification delay exceeded 40%, and the evaluation regarding the slab quality was not good. This is thought to be due to the following reasons.
That is, the fact that the casting speed is relatively high means that the discharge amount of molten steel from the immersion nozzle is relatively large. In short, since the discharge flow rate of the molten steel from the immersion nozzle is larger than that of the immersion nozzle, the time required for the molten steel discharged from the immersion nozzle to reach the solidified shell is reduced. That is, the molten steel discharged from the immersion nozzle reaches the solidified shell in an extremely high temperature state with almost no cooling, and as a result, excessive heat is supplied to the solidified shell, so that the solidification delay is delayed. It is thought that it was promoted. In addition, as the solidification delay is promoted, the evaluation regarding the slab quality deteriorates as described above.

<Test 6: degree of superheat>
In this test, as shown in Table 7 below, attention is paid to the degree of superheat.

Other test conditions not described in Table 7 are as follows.
--------------------
D = 85 [mm]
h = 25 [mm], y = 40 [mm], Y = 70 [mm]
θ1 = 10 [deg.], θ2 = 0 [deg.], θ3 = 55 [deg.], R1 = 2 [mm]
h / D = 0.29, y / Y = 0.57, θ2 / θ3 = 0
--------------------
Na = 60 [cm ² ], θ4 = 35 [deg.]
W = 1240 [mm], P = 240 [mm]
Vc = 0.9 [m / min], M-EMS = 550 [gauss]
--------------------

  In general, it is extremely difficult to keep the degree of superheat constant for a practical operation reason.

Although not shown in Table 7 above, in a test in which the degree of superheat ΔT [° C.] was less than 20 (a test with a degree of superheat ΔT [° C.] = 17), the molten steel solidified in the immersion nozzle. Gradually adhering to the inner wall surface of the immersion nozzle, the nozzle clogging of the immersion nozzle occurred soon. Needless to say, once the immersion nozzle causes nozzle clogging, continuous casting must be temporarily suspended.
Further, when the degree of superheat ΔT [° C.] is less than 20, even if the above reversal flow is formed appropriately, almost no heat can be supplied to the meniscus, so that the so-called skin of the meniscus can be obtained. Another problem was that tension (generated by melting the molten steel into a film) had occurred.

  On the other hand, as shown in Table 7 above, in the test in which the degree of superheat ΔT [° C.] exceeded 45, the degree of solidification delay exceeded 40%. This is probably because the molten steel discharged from the immersion nozzle becomes excessively high in temperature, and the supply of heat to the solidified shell being formed in the mold becomes excessive.

<Test 7: M-EMS>
In this test, as shown in Table 8 below, the in-mold electromagnetic stirring strength M-EMS [gauss] is focused.

Other test conditions not described in Table 8 are as follows.
--------------------
D = 85 [mm]
h = 25 [mm], y = 40 [mm], Y = 70 [mm]
θ1 = 10 [deg.], θ2 = 0 [deg.], θ3 = 55 [deg.], R1 = 2 [mm]
h / D = 0.29, y / Y = 0.57, θ2 / θ3 = 0
--------------------
Na = 60 [cm ² ], θ4 = 35 [deg.]
W = 1240 [mm], P = 240 [mm]
Vc = 1.0 [m / min]
--------------------

  As shown in Table 8 above, in the test in which the in-mold electromagnetic stirring strength M-EMS [gauss] was set to exceed 1000, the degree of solidification delay exceeded 40%, and the evaluation on surface defects after rolling was good. It wasn't.

The reason why the coagulation delay has exceeded 40% is considered to be due to the following reasons. That is, as described above, generally, by the discharge flow of molten steel discharged from the submerged nozzle (starting from the discharge hole and rising along the inner wall surface of the narrow mold side, the direction of the flow toward the submersible nozzle side is caused by the collision with the meniscus. The above reversal flow is formed. In general, the electromagnetic stirring in the mold is performed so as to stir the molten steel in the mold, particularly in the vicinity of the meniscus, by gently swirling around the immersion nozzle. Therefore, the reversal flow and the swirling flow of the molten steel by electromagnetic stirring collide with each other in the vicinity of the meniscus. As a result, normal, the inversion flow, by colliding with the swirling flow, the direction of the flow is forced to bend into the diagonal corners of the solidified shell of the hollow substantially rectangular in form of one column in the mold Therefore, the pair of diagonal corners of the solidified shell are more likely to cause a solidification delay because the heat supply is slightly greater than the other pair of diagonal corners. In this regard, when the electromagnetic stirring intensity M-EMS [gauss] in the mold is excessive, the swirl flow is generated more strongly, and thus the reversal flow is further curved, and as a result, the pair of pairs This is thought to be because heat is further supplied to the corners to further accelerate the solidification delay.

  Moreover, it is thought that it was based on the following reasons that evaluation about the surface flaw after rolling was not favorable. That is, the above swirling flow is generated strongly, and an excessive flow velocity is added to the molten steel near the meniscus, so that the meniscus undulates and the mold powder suspended on the meniscus is caught in the molten steel. It is considered to be a body.

As described above, in the present embodiment, the high carbon steel having a carbon content C [wt%] of 0.20 to 0.60 is continuously cast as follows.
That is, using the above-described immersion nozzle 100 having a predetermined shape and a mold having a predetermined mold width W and a mold thickness P, the casting speed Vc [m / min] is set to 0.8 to 1.6, and the degree of superheat ΔT. [℃] was 20 to 45, and either not performed at all or in the mold electromagnetic stirring intensity M-EMS [gauss] of the electromagnetic stirring and 1000, high-carbon steel is continuously cast.

According to this, since a useful immersion nozzle is employed, the drift of the molten steel discharge flow in the mold thickness direction can be reduced without hindering the effect of suppressing the splash phenomenon at the start of casting.
Moreover, the solidification delay of the solidified shell can be suppressed, and the surface quality and the like of the slab (equivalent items for evaluation of surface defects after rolling and slab quality in the above tests) can be improved.
More specifically, since the discharge flow in the mold thickness direction can be made substantially uniform by improving the drift in the mold thickness direction, heat is evenly supplied to the entire meniscus so that the powder is uniformly hatched. Since it is promoted, the above-mentioned biting of the unhatched powder is suppressed, and as a result, the slab with less vertical split can be cast.

  As mentioned above, although preferred embodiment of this invention was described, the immersion nozzle 100 mentioned above can be changed as follows.

  That is, the discharge holes 2 and 2 of the immersion nozzle 100 are formed in a substantially rectangular shape in the above embodiment, but are not limited thereto, and are formed in a circular shape described in FIG. Of course, it may be oval or trapezoidal.

The longitudinal cross-sectional view of the immersion nozzle which concerns on one Embodiment of this invention. FIG. 2 is a sectional view taken along line 2-2 in FIG. 1. The A section enlarged view in FIG. FIG. 4 is a sectional view taken along line 4-4 in FIG. The figure similar to FIG. The longitudinal cross-sectional view of the conventional immersion nozzle. The figure similar to FIG. The front view of an immersion nozzle. The figure which shows an example of the measurement result of the flow velocity of the water flow discharged from the discharge hole of an immersion nozzle. The figure which shows an example of the measurement result of the flow velocity of the water flow discharged from the discharge hole of an immersion nozzle. The side view of an immersion nozzle. The figure similar to FIG. The figure similar to FIG. The figure which displays together the cross section of the immersion nozzle shown in FIG. 2, and the casting_mold | template in which this immersion nozzle is inserted. Explanatory drawing of a coagulation delay degree. The figure which shows the other test result regarding a coagulation delay degree.

2 Discharge hole
2a Open end on the inner circumference side
100 immersion nozzle
200 molds
W Mold width
P Mold thickness θ4 angle
Vc casting speed
Src Surface perpendicular to the axis of the immersion nozzle ΔT Superheat
M-EMS electromagnetic stirring intensity in mold

Claims (1)

A pair of opposed discharge holes are drilled in the vicinity of the nozzle inner bottom surface, and a concave portion extending in the nozzle radial direction is formed in the nozzle inner bottom surface.
The vertical cross section in the longitudinal direction of the recess is rectangular or trapezoidal,
The side of the vertical cross section in the longitudinal direction of the recess is parallel to the longitudinal direction of the immersion nozzle or is inclined outwardly from 0 degree to 50 degrees or less with respect to the longitudinal direction of the immersion nozzle ,
The concave portion is an internal angle of a vertical cross section in the longitudinal direction, and is formed so that the one far from the inner bottom surface of the nozzle is 90 degrees or more and 140 degrees or less,
H / D, which is the ratio of the depth h of the vertical cross section in the longitudinal direction of the concave portion and the inner diameter D of the immersion nozzle, is in the range of 0.1 ≦ h / D ≦ 1.0,
Y / Y which is a ratio of the width y of the lower side of the vertical cross section in the longitudinal direction of the concave portion and the opening width Y of the inner circumferential side opening end of the discharge hole is 0.4 ≦ y / Y ≦ 1.0. Within the range of
And the direction of the discharge port is a direction connecting the opening center of the center point and the discharge hole of the nozzle inner diameter in a plan view, a longitudinal direction of the recess, the angle θ2 formed by the the direction of the discharge hole, the Θ2 / θ3, which is the ratio of the angle θ3 formed by the surface connecting the side of the inner peripheral opening end of the discharge hole and the axis of the immersion nozzle, is in the range of 0 ≦ θ2 / θ3 ≦ 1.0 Within
The opening area Na [cm ² ] of the inner circumferential side opening end of the discharge hole is 35 to 115,
The axis of said immersion nozzle, the better the direction of the discharge hole, the contour of the front end side of the immersion nozzle of the contour of the discharge holes appearing in the pair in the cross section including the plane perpendicular to the axis of said immersion nozzle And an immersion nozzle having an angle θ4 [deg.] Formed by -5 to 55,
A mold for cooling molten steel to form a solidified shell of a predetermined shape,
The mold width W [mm] at the upper end of the mold is 800-2100,
A mold having a mold thickness P [mm] at the upper end of the mold of 200 to 320;
Use
The casting speed Vc [m / min] is 0.8 to 1.6,
The degree of superheat ΔT [° C.] is set to 20 to 45,
Mold in electromagnetic stirring intensity M-EMS [gauss] as a 0 to 1000, and
A continuous casting method for high carbon steel, characterized by continuously casting a high carbon steel having a carbon content C [wt%] of 0.20 to 0.60.