JP5027625B2 - Immersion nozzle for continuous casting - Google Patents

Description

  The present invention relates to an immersion nozzle for continuous casting for pouring molten steel from a tundish to a mold, and more particularly to an immersion nozzle for continuous casting that does not cause operational troubles such as quality defects and breakout due to cracking of a cast piece.

  The tundish in a continuous casting facility is configured to receive molten steel by applying a refractory lining to the inner surface of the steel shell. A so-called immersion nozzle) is attached. This immersion nozzle has a role of preventing the molten steel flow from being exposed to air during pouring and oxidizing, and when pouring molten steel into the mold, the lower end of the molten nozzle is placed in the molten steel in the mold. Soaked in

  In continuous casting of steel, if the discharge flow of molten steel from the immersion nozzle collides intensively with a corner or the like where the cooling capacity of the slab is weak, the heat removal capacity of the slab is insufficient and a local solidification delay occurs. However, it causes quality defects due to cracks in the slab and operational troubles such as breakout. Therefore, it is necessary to reduce the collision flow velocity by diffusing the discharge flow of molten steel from the immersion nozzle before reaching the slab. In order to reduce non-uniformity of solidification, it is necessary to suppress temporal variation and spatial variation of the flow velocity of the discharge flow.

  In order to reduce the discharge flow rate of molten steel, it is sufficient to increase the cross-sectional area of the discharge hole, but if the cross-sectional area becomes too large, flow non-uniformity will occur in the discharge hole flow path and flow rate fluctuations will occur. It becomes easy. In addition, when the flow conditions inside the immersion nozzle fluctuate due to changes in operating conditions such as changes in the slide plate opening / closing amount, increase / decrease in the flow rate of blown Ar, and accumulation of deposits such as alumina in the internal flow path of the immersion nozzle, Similarly, the discharge flow is likely to fluctuate. For this reason, a technique has been proposed in which the velocity distribution is made uniform from the discharge holes of the immersion nozzle and the fluctuation of the flow in the immersion nozzle is suppressed.

  In the immersion nozzle according to such a conventional example, the shape of the discharge hole is improved such as making the cross-sectional shape of the discharge hole concave or providing a stepped portion whose diameter increases toward the outside (see, for example, Patent Documents 1 and 2). ) Improvement of the peripheral shape of the discharge hole, such as providing a ridge-like protrusion on the bottom surface of the hot water reservoir inside the nozzle (see, for example, Patent Document 3), Improvement (for example, see Patent Documents 4 and 5), or a configuration that satisfies a certain relational expression such as dimensions of discharge holes and internal flow paths, discharge flow velocity, etc. (see, for example, Patent Documents 6 and 7) Proposals have been made.

JP-A-2-169160 JP 2002-66729 A International Publication Number WO2005 / 070589 JP 2004-122226 A JP 2005-296971 A JP 2004-209512 A JP 2005-28385 A

  However, if the shapes of the discharge holes and the hot water pool are complicated, it is difficult to process the immersion nozzle, leading to an increase in cost. Also, if a large number of protrusions and recesses are provided, it will be difficult to process the immersion nozzle and the cost will be increased, and the shape will change due to melting damage and deposits, which will reduce the effect during use. May be trapped by the slab and cause product defects. In addition, when the configuration is such that the dimensions of the discharge holes and the internal flow path, the discharge flow rate, etc. satisfy a certain relational expression, if the relational expression is complicated, the setting becomes complicated, and the dimensions are also constantly in production management. There are problems such as confirmation of changes.

  As a means for stabilizing a flow traveling in one direction, a swirling flow system that adds a rotational motion with the flow direction as a rotation axis is used for a combustion nozzle or the like. However, since the molten steel flow velocity in the internal flow path of the immersion nozzle is slower than the gas in the combustion nozzle, the direction of the swirl flow is not stable and it is difficult to apply.

  Therefore, the object of the present invention is not to cause operational troubles such as quality defects and breakout due to cracking of the slab by reducing the molten steel flow velocity from the immersion nozzle and the molten steel flow velocity fluctuation without having a complicated mechanism. It is to provide an immersion nozzle for continuous casting.

  In view of the above circumstances, when the inventors generate a pair of swirling flows (twin vortices) that swirl in opposite directions to the discharge flow, the induced speed that the vortices impart to other fluids always faces a certain direction. Thus, the present invention has been made based on the knowledge that the swirling flow is stabilized even at a low flow velocity, and that the flow velocity can be reduced by converting the straight flow energy into vortices.

In order to achieve the above object, the means employed by the continuous casting immersion nozzle according to claim 1 of the present invention has a flow rate adjusting mechanism in the upper part, a pair of discharge holes facing the lower part is formed, and the flow direction In a continuous casting immersion nozzle having a circular cross-section internal flow passage that permits a change in diameter, the ratio W _SN / H _SN of the width W _SN to the height H _SN at the outermost portion of the discharge hole is _expressed by the following equation (1): And the ratio A _SN / A _IN between the discharge hole total cross-sectional area A _{SN at} the outermost part of the pair of discharge holes and the cross-sectional area A _IN of the internal flow path directly above the discharge hole is expressed by the following equation (2) Further, the ratio of the length L _nozzle of the internal flow path from the lower end of the flow rate adjusting mechanism to the upper end of the discharge hole and the diameter D _IN of the internal flow path directly above the discharge hole is L _nozzle / D _IN Is configured to satisfy the condition of the following expression (3).

1.6 <W _SN / H _SN <2.3 (1)
A _SN / A _IN <2.6 (2)
L _nozzle / D _IN > 6.0 …… (3)

The means employed by the continuous casting immersion nozzle according to claim 2 of the present invention is the continuous casting immersion nozzle according to claim 1, wherein the following formula (5) A first protrusion having a height Ht _nozzle that satisfies the above condition is provided.
_{Ht nozzle / H SN> 0.15 ......} (5)

The means employed by the continuous casting immersion nozzle according to claim 3 of the present invention is the continuous casting immersion nozzle according to claim 1 or 2, when the cross section immediately above the discharge hole of the internal flow path is viewed in plan view. , the circumferential position perpendicular to the center line of the discharge hole, the second protrusion of the height H that protrudes from the internal flow path wall in conditions of less than Shi the cross section of the following formula (6), a pair disposed facing It is characterized by being made.
L _top / H <5.0 (6)
here,
L _top : Distance from the lower end of the second protrusion to the upper end of the discharge hole

According to the continuous casting immersion nozzle of the first aspect of the present invention, the flow control mechanism is provided in the upper part, the pair of discharge holes facing the lower part is formed, and the circular cross section that allows a change in diameter in the flow direction is formed. In the continuous casting immersion nozzle having an internal flow path , the ratio W _SN / H _SN of the width W _SN to the height H _SN at the outermost part of the discharge hole satisfies the condition of the previous formula (1), and the pair of pairs The ratio A _SN / A _{IN of the} total cross sectional area A _SN of the outermost discharge hole and the cross sectional area A _IN of the internal flow path directly above the discharge hole satisfies the condition of the above formula (2), and further, the flow rate The ratio L _nozzle / D _IN between the length L _nozzle of the internal flow path from the lower end of the adjusting mechanism to the upper end of the discharge hole and the diameter D _IN of the internal flow path directly above the discharge hole satisfies the condition of the previous formula (3) It is structured like this.

  As a result, even if fluctuations occur in the internal flow velocity distribution, the number of vortex generation modes is limited to two, and twin vortices are always generated stably, so fluctuations in the discharge flow of molten steel from the immersion nozzle are suppressed. Since the discharge flow of molten steel from the immersion nozzle is diffused well before reaching the slab, the heat removal capability of the slab is insufficient and local solidification delay occurs, resulting in quality defects due to cracking of the slab And troubles such as breakout will not occur.

Further, according to the continuous casting immersion nozzle according to claim 2 of the present invention, in the continuous casting immersion nozzle according to claim 1, the above formula (5) Since the first protrusion of the height Ht _nozzle satisfying the above condition is provided, the flow in the swirling direction is divided at the center, and twin vortices are generated even under the condition that normally one vortex is generated. A stable discharge flow is formed.

Furthermore, according to the continuous casting immersion nozzle according to claim 3 of the present invention, in the continuous casting immersion nozzle according to claim 1 or 2, when the cross section of the internal flow path immediately above the discharge hole is viewed in plan view. , the circumferential position perpendicular to the center line of the discharge hole, the second protrusion of the height H that protrudes from the internal flow path wall in conditions of less than Shi the cross section of the following formula (6), a pair disposed facing Thus, the flow of molten steel is separated after passing through the protrusions to generate two wake vortices, and has the effect of promoting the growth of the twin vortices.

  A basic configuration of an immersion nozzle for continuous casting according to an embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a schematic elevational sectional view showing the entire immersion nozzle according to the embodiment of the present invention. 2 shows the details of the X part of FIG. 1, FIG. 2A is a partially enlarged view of the X part, FIG. 2B is a cross-sectional view taken along the line YY of FIG. 1A, and FIG. It is the figure which looked at the discharge hole of (a) from the outer side along the discharge hole centerline. FIG. 3 is a conceptual diagram showing the flow state of molten steel in the vicinity of the discharge hole due to the difference in the ratio between the width and height of the discharge hole. FIG. In the case of 0, FIG. (B) shows the case where the ratio of the width and height at the outermost part of the discharge hole is 2.0. 4A and 4B are conceptual diagrams showing a change in the mode of the discharge flow when the ratio of the width and height at the outermost portion of the discharge hole is changed. FIG. 4A is a vortex generation state, and FIG. Indicates the degree.

  First, as shown in FIGS. 1 and 2, an immersion nozzle 1 according to an embodiment of the present invention has a pair of a slide plate (flow rate adjusting mechanism) 2 at the top and a pair of opposed nozzles 1 facing the center of the immersion nozzle 1 at the bottom. A discharge hole 3 is provided. Then, the molten steel M is attached to the tundish (not shown) in the vertical direction via the slide plate 2 for controlling the amount of the molten steel M to be discharged, and from the pair of discharge holes 3 provided in the lower part of the molten steel M to the mold during casting. It is configured to pour hot water.

  The molten steel M that has flowed into the internal flow path 4 of the immersion nozzle 1 via the slide plate 2 has a boundary layer in which the flow velocity is substantially uniform in the flow direction on the upstream side except for the vicinity of the inner wall surface of the internal flow path 4. Forms an undeveloped flow F1, while on the downstream side, it flows down while forming a flow F2 in which a boundary layer is developed, and after colliding with the pool 4a, it is discharged from the discharge hole 3 to the mold.

  As shown in FIGS. 2A and 2B, a pair of the discharge holes 3 are disposed on the upper side of the hot water reservoir 4 a so as to face a horizontal position orthogonal to the center line of the immersion nozzle 1. Each of them is formed so as to have a discharge angle θ downward from a horizontal plane perpendicular to the center line of 1. Further, the width and height of these discharge holes 3 are not necessarily constant at an arbitrary cut surface perpendicular to the center line of the discharge holes 3. For example, as shown in FIGS. While increasing from the outside to the outside, the height is constant.

  Next, in the configuration of the immersion nozzle 1 according to the embodiment of the present invention, numerical analysis is performed on the flow state of the molten steel in the vicinity of the discharge hole 3 when the ratio of the width and height of the discharge hole 3 is changed. Based on the result, it demonstrates below, referring attached FIG.

  In the internal flow path 4 on the downstream side of the immersion nozzle 1, a molten steel flow F <b> 2 with a developed boundary layer is formed as described above, and the molten steel near the center in the width direction of the flow F <b> 2 is formed on the bottom surface of the internal flow path 4. While forming the orthogonal flow F3a discharged from the discharge hole 3 without colliding with a certain hot water reservoir 4a, the molten steel near both ends in the width direction of the boundary layer flow F2 is the hot water reservoir that is the bottom surface of the internal flow path 4 After colliding with 4a, the upward flow F3b is formed and discharged toward the discharge hole 3 arranged at the upper part of the hot water reservoir 4a. When the direct flow F3a and the upward flow F3b are combined, a vortex V is formed in the discharge flow.

Since the vortex V is stable in a circular state, when the ratio W _SN / H _SN of the width W _SN to the height H _{SN at} the outermost part of the discharge hole 3 is close to 1.0, as shown in FIG. Since the upward flow F3b is undeveloped, the direct flow F3a is dominantly formed. However, as shown in FIG. 4A, such a vortex V has one rightward direction and one leftward direction. Since various modes are taken under the influence of the flow fluctuations inside the immersion nozzle 1 such as two or two at the bottom, the discharge flow becomes unstable.

Further, when the width W _{SN at the} outermost part of the discharge hole 3 approaches three times the height H _SN , there is a mode in which three vortices are generated as shown in FIG. Is not stable. On the other hand, when the width W _SN discharge holes 3 outermost immersion nozzle 1 to 2 times the vicinity of the height H _SN, as shown in FIG. 3 (b) and FIG. 4 (a), the said upflow F3b develops, The discharge flow from the pair of discharge holes 3 is a flow in which twin vortices V1 and V2 that rotate in a pair of opposite directions are formed.

That is, in the immersion nozzle 1 according to the present invention, the ratio W _SN / H _SN of the width W _SN to the height H _{SN at} the outermost part of the discharge hole 3 preferably satisfies the condition of the following formula (1). If the ratio W _SN / _HSN is 1.6 or less, the generation of the vortex V becomes unstable, and if the ratio _WSN / _HSN is 2.3 or more, three vortices are generated. The direction is not constant, and in any case, as shown in FIG. 4 (b), the drift tends to occur, and the discharge flow becomes unstable.

From the above results, in order to stably form the pair of twin vortices V1 and V2 in each discharge flow, the width W _SN at the outermost part of the discharge hole 3 needs to be close to twice the height H _SN . In this state, even if the internal flow velocity distribution fluctuates, the number of vortex generation modes is limited to two in each discharge flow, so twin vortices V1 and V2 are always generated in each discharge flow. Fluctuations are suppressed.
1.6 <W _SN / H _SN <2.3 (1)

At the same time, the ratio A _SN / A _IN between the total cross sectional area A _{SN of the} outermost pair of the discharge holes 3 and the cross sectional area A _IN of the internal flow path 4 immediately above the discharge holes 3 satisfies the condition of the following equation (2): The ratio L _nozzle / D _IN of the length L _nozzle of the internal flow path 4 from the lower end of the slide plate 2 provided at the upper part of the immersion nozzle 1 to the upper end of the discharge hole 3 and the diameter D _IN of the internal flow path 4 is as follows: It is preferable to be configured so as to satisfy the condition of Expression (3). The ratio A _SN / A _{IN is set} to 2.6 or more, and the total cross-sectional area A _SN of the discharge hole 3 is abruptly larger than the cross-sectional area A _IN of the internal flow path 4 of the nozzle 1 or the ratio L _nozzle / D _IN If the length of the internal flow path 4 is shortened to 6.0 or less, the flow velocity distribution of the molten steel deviates from the boundary layer shape, and it is difficult to generate vortices.
A _SN / A _IN <2.6 (2)
L _nozzle / D _IN > 6.0 …… (3)

  Next, in the configuration of the immersion nozzle according to the embodiment of the present invention, in the case where a protrusion is provided in the vicinity of the discharge hole of the immersion nozzle, based on the result of numerical analysis of the flow state of the molten steel in the vicinity of the discharge hole, the following This will be described with reference to FIGS. Fig.5 (a) is a conceptual diagram showing the flow condition of the molten steel in a discharge hole at the time of providing the 1st protrusion part in the center of the width direction in the flow path lower part of a discharge hole, FIG.5 (b) is a figure (a). It is sectional drawing which shows arrow ZZ. FIG. 6A is a conceptual diagram showing a flow state of the molten steel in the vicinity of the discharge hole when the second protrusion is provided in the internal flow path immediately above the discharge hole, and FIG. 6B is a view of FIG. It is sectional drawing which shows arrow WW.

In the immersion nozzle 1 according to the present invention, it is preferable that a first protrusion 5 having a height Ht _nozzle satisfying the following expression (5) is provided at the center in the width direction of the flow path lower part 3 a of the discharge hole 3. If the first protrusion 5 satisfying the equation (5) is provided at the center in the width direction of the flow path lower part 3a of the discharge hole 3, the flow in the swirling direction is divided at the center, and normally one vortex is generated. Even under the conditions, twin vortices V1 and V2 are generated in each discharge hole. If the ratio _Ht nozzle / H _SN of the formula (5) is 0.15 or less, the height of the first protrusion 5 is insufficient, under normal to the conditions in which one vortex is generated, stable Thus, the twin vortices V1 and V2 cannot be generated in each discharge hole.
_{Ht nozzle / H SN> 0.15 ......} (5)

Furthermore, in the immersion nozzle 1 according to the present invention, the second protrusion 6 having a height H that satisfies the condition of the following expression (6) is located directly above the discharge hole 3 of the internal flow path 4, and the center line of the discharge hole 3. It is preferable that a pair of them be arranged at positions orthogonal to each other. Here, L _top is the distance from the lower end of the second protrusion 6 in the flow path to the upper end of the discharge hole 3. When the second protrusion 6 arranged in this way is provided immediately above the discharge hole 3 of the internal flow path 4 in the immersion nozzle 1, the flow of the molten steel is separated after passing through the second protrusion 6 and is separated into two pieces. The wake vortices V3 and V4 are generated.
L _top / H <5.0 (6)

When the center of the generated wake vortex V3, V4 flows into the discharge hole 3, it has the same swirling direction as the twin vortices V1, V2, and facilitates the vortex generation of the discharge flow. If the ratio L _top / H of the above equation (6) is 5.0 or less, the height of the second protrusion 6 is insufficient, and therefore it is insufficient to promote the generation of the twin vortices V1 and V2 of the discharge flow. It becomes.

As described above, in the immersion nozzle 1, the first protrusion 5 having a height Ht _{nozzle that} satisfies the condition of the previous formula (5) is provided at the center in the width direction of the flow path lower part 3 a of the discharge hole 3, or the internal flow By directly placing the second protrusion 6 having a height H that satisfies the condition of the above equation (6) in a position directly above the discharge hole 3 in the path 4, the position is perpendicular to the center line of the discharge hole 3. The generation of twin vortices V1 and V2 can be facilitated.

<Example>
In order to verify the effectiveness of the immersion nozzle for continuous casting according to the present invention, an example in which a numerical experiment by flow simulation is performed will be described below with reference to FIGS. FIG. 7 is a perspective view showing a trajectory line of a discharge flow of molten steel in a bloom continuous caster, and FIG. 7A is a diagram in the case of the embodiment according to the present invention (W _SN / H _SN = 2). Indicates a comparative example (W _SN / H _SN = 1).

  In the case of the comparative example, the discharge flow forms one vortex with respect to one discharge hole, but there is a fast flow that collides with the mold side wall and an unstable flow toward the molten metal surface. The distribution shapes of the left and right discharge flows are also different. On the other hand, in the case of the example, it was confirmed that a pair of twin vortices were generated for one discharge hole in the discharge flow, and the flow was stable on the left and right.

Next, FIG. 8 is a diagram showing a simulation result by changing the ratio W _SN / H _SN of the width W _SN and the height H _{SN at} the outermost portion of the discharge hole, at a position 200 mm away from the discharge hole. The difference between the maximum value of the discharge flow and the maximum value of each discharge flow separated in the left and right directions is shown. The maximum value of the flow velocity is about 60% in the vicinity of the ratio W _SN / H _SN = 2 and the ratio W _SN / H _SN = 1, and it can be seen that the discharge flow is greatly decelerated. . From the above results, the ratio W _SN / H _SN is preferably in the range of 1.6 <W _SN / H _SN <2.3, and more preferably in the range of 1.8 <W _SN / H _SN <2.2. Was confirmed.

FIG. 9 shows the discharge hole total cross-sectional area A _{SN at the} outermost pair of discharge holes and the above-mentioned ratio of the width W _{SN at the} outermost part of the discharge holes and the ratio W _SN / H _SN = 1.8 of the height H _SN. discharge hole is a graph showing a result of simulation by changing the ratio a _SN / a _iN of the cross-sectional area a _iN of the internal flow path immediately above, the discharge flow of the left and right maximum similarly discharge flow and FIG. 8 Indicates the difference between the maximum values. When the ratio A _SN / A _IN exceeds 2.6, the maximum flow rate increases rapidly, and the effect of specifying the discharge hole ratio W _SN / H _SN is lost. Therefore, it was confirmed that the range of the ratio A _SN / A _IN <2.6 was desirable.

As described above, according to the continuous casting immersion nozzle according to the present invention, in the continuous casting immersion nozzle having a pair of opposed discharge holes, the ratio W _SN / HS _N satisfies the condition of the previous formula (1), In addition, the ratio A _SN / A _IN satisfies the condition of the previous formula (2), and the ratio L _nozzle / D _IN further satisfies the condition of the previous formula (3). Even if the fluctuation occurs, the number of vortex generation modes is limited to two, so twin vortices Va and Vb are always generated, and fluctuations in the discharge flow are suppressed. Furthermore, it is possible to promote the generation of twin vortices by providing a first protrusion at the center in the width direction of the flow path below the discharge hole, or by providing a second protrusion directly above the discharge hole of the internal flow path. It is.

for that reason,
Even if fluctuations occur in the internal flow velocity distribution, twin vortices are always generated stably, so fluctuations in the molten steel discharge flow from the immersion nozzle are suppressed, and the molten steel discharge flow from the immersion nozzle reaches the slab. Since it diffuses well before, the heat removal capability of the slab is insufficient and a local solidification delay occurs, causing no operational defects such as quality defects and breakout due to cracking of the slab.

It is a typical elevation sectional view showing the whole immersion nozzle concerning an embodiment of the invention. FIG. 1 shows the details of the X part in FIG. 1, FIG. 1 (a) is a partially enlarged view of the X part, FIG. 2 (b) is a sectional view showing the arrow Y-Y in FIG. 1 (a), and FIG. It is the figure which looked at this discharge hole from the outer side along the discharge hole centerline. It is a conceptual diagram showing the flow situation of the molten steel near the discharge hole due to the difference in the ratio between the width and height of the discharge hole. FIG. (A) is a case where the ratio of the width and height at the outermost part of the discharge hole is 1.0 FIG. 5B shows a case where the ratio of the width and height at the outermost part of the discharge hole is 2.0. It is a conceptual diagram showing the change of the mode of the discharge flow when the ratio of the width and height at the outermost part of the discharge hole is changed. FIG. (A) shows the vortex generation state, and FIG. Show. Fig. (A) is a conceptual diagram showing the flow state of molten steel in the discharge hole when the first protrusion is provided at the center in the width direction at the lower part of the flow path of the discharge hole, and Fig. (B) is a diagram of Fig. (A). It is sectional drawing which shows arrow ZZ. Fig. (A) is a conceptual diagram showing the flow of molten steel in the vicinity of the discharge hole when the second protrusion is provided in the internal flow path directly above the discharge hole, and Fig. (B) is an arrow in Fig. (A). It is sectional drawing which shows view WW. It is a perspective view which shows the trajectory line of the discharge flow of the molten steel in a bloom caster, The figure (a) is an Example ( _WSN / _HSN = 2) based on this invention, A figure (b) is a comparative example The case of (W _SN / H _SN = 1) is shown. The ratio W _SN / H _SN width W _SN and height H _SN discharge holes outermost change shows the results of simulation, the maximum value of the discharge flow at a position away 200mm outwardly from the discharge hole and The difference in the maximum value of each discharge flow that separates in the left and right directions is shown. The ratio of the outermost width W _SN of the discharge holes to the height H _SN is a constant ratio W _SN / H _SN = 1.8, and the discharge hole total cross sectional area A _{SN at the} outermost pair of discharge holes and immediately above the discharge holes is a diagram showing a result of simulation by changing the ratio a _SN / a _iN of the cross-sectional area a _iN of the internal flow channel, the difference between the maximum value of the discharge flow of the left and right maximum value similarly discharge flow and FIG. 8 Indicates.

Explanation of symbols

M: Molten steel,
F1: Flow of molten steel with undeveloped boundary layer, F2: Flow of molten steel with developed boundary layer,
F3a: Direct flow, F3b: Upflow,
V: Vortex, V1, V2: Twin vortex, V3, V4: Wake vortex,
1: immersion nozzle, 2: slide plate (flow rate adjusting mechanism),
3: discharge hole, 3a: lower part of flow path of discharge hole,
4: Internal flow path, 4a: Hot water reservoir,
5: First protrusion, 6: Second protrusion

Claims (3)

In a continuous casting immersion nozzle having a flow rate adjusting mechanism in the upper part and a pair of discharge holes facing the lower part, and having a circular cross-section internal flow passage that allows a change in diameter in the flow direction, the outermost of the discharge holes. The ratio W _SN / H _SN of the width W _SN to the height H _{SN at} the outside satisfies the condition of the following expression (1), and the discharge hole total sectional area A _{SN at} the outermost part of the pair of discharge holes and the discharge holes The ratio A _SN / A _IN of the sectional area A _IN of the internal flow path directly above satisfies the condition of the following equation (2), and the length of the internal flow path from the lower end of the flow rate adjusting mechanism to the upper end of the discharge hole An immersion nozzle for continuous casting, characterized in that the ratio L _nozzle / D _IN between the diameter L _nozzle and the diameter D _IN of the internal flow path directly above the discharge hole satisfies the condition of the following formula (3).
1.6 <W _SN / H _SN <2.3 (1)
A _SN / A _IN <2.6 (2)
L _nozzle / D _IN > 6.0 …… (3) 2. The continuous casting according to claim 1, wherein a first protrusion having a height of Ht _{nozzle that} satisfies the following expression (5) is provided at the center in the width direction at the lower portion of the flow path of the discharge hole. Immersion nozzle.
_{Ht nozzle / H SN> 0.15 ......} (5) A plan view of the cross section in the discharge holes directly above the internal channel projecting, circumferentially positioned perpendicular to the center line of the discharge hole, from the internal flow path wall in the cross-sectional Shi meet the condition of the following formula (6) The continuous casting immersion nozzle according to claim 1, wherein a pair of second protrusions having a height H to be arranged are arranged to face each other.
L _top / H <5.0 (6)
here,
L _top : Distance from the lower end of the second protrusion to the upper end of the discharge hole