JP2007125575A - Method for continuously producing cast slab - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To produce a high quality cast slab less in inclusion of mold powder by suppressing the variation of molten metal surfaces in a mold caused by the unstable bulging between rolls of the solidified shell when the cast slab is continuously cast. <P>SOLUTION: In the method for producing the cast slab by continuously casting molten steel while suppressing the variation of the molten steel surface in the mold caused by the unstable bulging of the solidified shell, the continuous casting is performed by providing a pair of facing mold long side walls 2a and a pair of facing mold short side walls 2b, and using the tapered mold 2 in the facing short side walls so that the tapered amount (Δt) defied by expression (1): ΔT(%)=(Wu-Wl)×100/L becomes in the range of 1.1 to 1.3%, wherein Wu is an interval between the upper ends of the facing mold short side walls, Wl is an interval between the lower ends thereof and L is a length in the perpendicular direction of the mold short side wall. Thus, the solidified shell thickness in the mold is uniformed, thereby suppressing the variation of the molten steel surfaces in the mold. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  In the present invention, when continuously casting a slab slab, high-quality continuous casting with less mold powder entrainment is prevented by preventing cyclic fluctuations in the mold caused by bulging between rolls of the solidified shell. The present invention relates to a method for manufacturing a slab.

  In continuous casting of steel, controlling the molten steel level in the mold is extremely important not only for stable operation but also for ensuring the quality of the cast slab. Conventionally, PI control is often used as a level control method for the mold surface in the mold. The control method in this case is to measure the molten steel surface level of the molten steel in the mold, adjust the opening of the flow adjusting device such as the sliding nozzle and stopper based on this measured value by PI control, This is a method of balancing the mass balance with the molten steel injected from the tundish.

  However, in continuous casting of slab slabs, even if level control as described above is performed, long-term mold surface fluctuations may occur. FIG. 1 shows an example of mold surface fluctuation and casting speed (also referred to as “slab drawing speed”) in continuous casting of slab slabs. In FIG. 1, in the casting area A, the molten metal surface level in the mold is small and the molten metal surface level is stable, but in the casting region B, the cyclic molten metal surface fluctuation occurs. The casting speed is reduced according to the occurrence. The period of this periodic mold surface fluctuation is several seconds to several tens of seconds, and the amplitude reaches several mm to several tens of mm. When such a phenomenon occurs, the mold powder added into the mold is entrained by the vertical movement of the molten steel in the mold, or the molten steel overflows from the mold under conditions where the amount of molten metal fluctuation increases with time. Therefore, there are cases where it is difficult not only to lower the quality of the slab but also to continue the casting itself.

  Therefore, when this periodic fluctuation of the molten metal surface occurs, the casting speed is usually lowered to wait for the molten metal surface fluctuation amount to decrease as shown in FIG. Making it lead to a decrease in production efficiency. Even if the casting can be continued without reducing the casting speed, the quality of the slab is deteriorated due to the entrainment of the mold powder as described above.

  The cause of the periodic fluctuation of the molten metal surface can be considered as follows. That is, as schematically shown in FIG. 2, the relationship between the bulging of the solidified shell and the fluctuation of the molten metal surface in the mold, the solidified shell 10 is bulged in a convex shape between the rolls of the slab support roll 8 by static iron pressure. When the part (convex part) reaches the next slab support roll 8 by pulling out the slab, the bulging part does not return along the slab support roll 8 and part of the solidified shell 10 is deformed. As a result, a phenomenon occurs in which the slab is pushed back to the unsolidified portion side while leaving the bulging portion. Such a bulging phenomenon is generally called “unsteady bulging”. If this unsteady bulging occurs at the same roll pitch in a continuous section and at each roll part, the solidified shell of the slab is pushed back to the unsolidified part side all at once, and conversely the roll The movement pushed out in between occurs periodically with the drawing of the slab. It is thought that this causes long-term fluctuations in the molten metal surface as shown in FIG. Hereinafter, this hot water surface fluctuation is referred to as “bulging hot water surface fluctuation”. In FIG. 2, 2a is a long side of the mold, 8 is a slab support roll, 10 is a solidified shell, 11 is an unsolidified portion, and 12 is a molten steel surface.

  As described above, as a means of solving the bulging surface level fluctuation, as described above, the casting speed is reduced, the thickness of the solidified shell between the bulging rolls is increased, the bulging amount is reduced, and the level fluctuation amount is reduced. There is a way to make it smaller. However, in this method, how much the casting speed is reduced is mostly determined by the experience of the casting operator, and the countermeasure is not quantitative, and excessive deceleration reduces the productivity of continuous casting.

  Further, Patent Document 1 discloses that when the periodicity of the current value of the pinch roll motor and the periodicity of the composite value of either or both of the molten metal surface level value and the molten metal surface control signal value coincide, Therefore, at least one of the change of the molten metal level control gain, the change of the casting speed, and the change of the secondary cooling condition is performed. However, in Patent Literature 1, it is not clear how much these conditions are changed to suppress bulging hot water surface fluctuation, and a certain amount of change is repeatedly performed to converge the bulging hot water surface fluctuation. . Therefore, in this method, if the amount of change at one time is too small, it takes time to converge the amount of fluctuation of the bulging hot water surface. On the other hand, if the amount of change at one time is too large, overshoot may occur. In addition, this method takes measures after unsteady bulging occurs in actual operation, and cannot be used as a means for presetting the casting conditions such that fluctuations in the bulging level are unlikely to occur.

  Furthermore, Patent Document 2 proposes a specific value for secondary cooling in order not to cause fluctuations in the bulging level, but as a precondition, the casting speed is 0.5 to 1.2 m / Since the conditions such as min and the slab width of 700 to 1380 mm and the slab thickness of 150 to 200 mm are attached, it is difficult to apply to casting conditions outside this range.

By the way, in the mold for slab continuous casting, in order to improve the contact between the solidified shell and the mold, the long mold side and / or the short mold side is narrowed so that the opposed mold surface becomes narrower downward ( (Hereinafter, referred to as “taper”) is often provided (see, for example, Patent Documents 3, 4, 5, and 6), but reports that clarify the relationship between mold taper and bulging level fluctuation have not yet been made. Absent.
Japanese Patent Laid-Open No. 11-170021 JP-A-7-303951 JP-A-4-258347 Japanese Utility Model Publication No. 5-70748 JP-A-10-128501 JP 2003-305544 A

  As described above, the conventional method for preventing fluctuations in the bulging hot water level cannot be predicted in advance based on the casting conditions or can be predicted but cannot be applied to a wide range of casting conditions. In reality, there is still a lot of room for improvement.

  The present invention has been made in view of the above circumstances, and the object is to continuously cast a steel slab slab, even under high-speed casting conditions, particularly at a casting speed of 2.0 m / min or more. Even in high-speed casting, high-quality continuous cast slabs with less mold powder entrainment are produced by suppressing fluctuations in the bulging surface in the mold caused by unsteady bulging between the rolls of the solidified shell. Is to provide a way to do.

  The inventors of the present invention have conducted intensive studies and studies to solve the above problems. The following describes the results of research and examination.

  As a result of investigating bulging surface fluctuation due to unsteady bulging under various casting conditions, in order to suppress bulging surface fluctuation, the thickness of the solidified shell is proposed as described in Patent Document 2 described above. It is important to reduce the bulging amount between the rolls by increasing the thickness of the roll, but it is also important to make the solidified shell thickness uniform in the width direction of the slab and in the casting direction of the slab. I understood. That is, by making the solidified shell thickness uniform, even if the solidified shell was bulged between the rolls of the slab support roll by static iron pressure, this bulging part reached the next slab support roll by pulling out the slab. It has been found that sometimes it returns to its original shape along the slab support roll and unsteady bulging is less likely to occur. This is considered to be due to the fact that the thickness of the solidified shell is made uniform, whereby the phenomenon that a part of the solidified shell as shown in FIG. In other words, it is considered that the non-uniformity of the solidified shell thickness causes deformation of the solidified shell and induces unsteady bulging.

  In this case, in the secondary cooling zone, it is not possible to arbitrarily change the cooling capacity at a specific position of the slab during casting. Therefore, it is attempted to make the solidified shell thickness uniform in the secondary cooling zone immediately below the mold. Since it is difficult, it has been found that it is necessary to make the cooling in the mold uniform in order to form a uniform solidified shell. That is, it has been found that it is necessary to cool uniformly without generating an air gap between the solidified shell and the mold in the mold.

  Therefore, a method for uniform cooling in the mold was studied for continuous casting of slab slabs. The casting speed at that time was set to 1.5 m / min or more in consideration of high productivity. As a result, the short side of the mold placed between a pair of opposed long mold sides is tapered so that the surface interval between the opposed short mold sides becomes narrower in the casting direction, and this taper amount is appropriately set. By setting the value so that the solidified shell near the short side of the slab and the long side of the mold are always in contact with each other, It has been found that the formation of gaps is prevented and uniform cooling is achieved while simultaneously increasing the thickness of the solidified shell.

  In this case, it is well known that the cooling of the solidified shell by the mold is performed via the mold powder. Therefore, the mold powder itself also uses a highly crystalline mold powder, so that the cooling effect of the mold is lowered. However, it was found that uniform mold cooling was obtained, and that the thickness of the solidified shell was further uniformed.

  That is, by applying an appropriate taper to the short side of the mold, and preferably using a mold powder with appropriate characteristics, even between high-speed castings with a casting speed of 2.0 m / min or more, between the rolls of the solidified shell It was found that the fluctuation of the molten metal surface in the mold caused by unsteady bulging can be suppressed. In this case, it is preferable to taper the long side of the mold, but in the case of a slab slab having a large width relative to the thickness of the slab, the long side solidified shell at the central portion in the width direction that does not receive the restraining force of the short side solidified shell Since it is always pressed against the long side of the mold by static iron pressure, it is not very important to taper the long side of the mold from the viewpoint of preventing the air gap, only the taper of the short side of the mold It was found that is sufficient.

  The present invention has been made on the basis of the above knowledge, and the method for manufacturing a continuous cast slab according to the first invention suppresses fluctuations in the mold surface in the mold caused by unsteady bulging of the solidified shell. A method for producing a continuous cast slab for continuously casting molten steel to produce a slab slab, comprising a pair of opposed mold long sides and a pair of opposed mold short sides, at the upper end of the opposed mold short sides When the interval is Wu, the lower end interval is Wl, and the length of the mold short side in the vertical direction is L, the taper amount (ΔT) defined by the following equation (1) is 1.1 to 1.3%. Continuous casting using a mold having a taper on the short side of the mold opposite to be within the range, uniformizing the thickness of the solidified shell in the mold, thus suppressing fluctuations in the molten metal surface in the mold It is what. In the equation (1), ΔT is the taper amount (%), Wu is the distance (m) between the upper ends of the opposite mold short sides, Wl is the distance (m) between the lower ends of the opposite mold short sides, and L is the mold short. It is the length (m) of the side in the vertical direction.

In the method for producing a continuous cast slab according to the second invention, in the first invention, the basicity (CaO / SiO ₂ ) is in the range of 0.85 to 1.00 on the surface of the molten steel in the mold. It is characterized by adding mold powder.

  The method for producing a continuous cast slab according to the third invention is characterized in that, in the first or second invention, the casting speed of the slab slab is 2.0 m / min or more.

According to the present invention, the taper of 1.1 to 1.3% is applied to the opposite mold short sides, and more preferably, the basicity (CaO / SiO ₂ ) is in the range of 0.85 to 1.00. Since a highly crystalline mold powder is used, even in the case of high-speed casting at a casting speed of 2.0 m / min or more, the cooling in the mold is made uniform to obtain a solidified shell with a uniform thickness. Unsteady bulging between rolls is suppressed, and fluctuations in the bulging level in the mold caused by unsteady bulging can be suppressed. As a result, it is possible to stably produce a high-quality slab free of mold powder with high productivity, which brings about an industrially beneficial effect.

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 3 is a schematic side view of the periphery of the mold of the continuous slab casting machine used in carrying out the present invention, and FIG. 4 is a schematic perspective view of the mold shown in FIG.

  In FIG. 3, a tundish 1 is disposed at a predetermined position above the mold 2 of the slab continuous casting machine, and a sliding nozzle 3 and an immersion nozzle 4 are disposed at the bottom of the tundish 1. The molten steel 9 once retained is injected into the mold 2 through the sliding nozzle 3 and the immersion nozzle 4. The sliding nozzle 3 has a three-plate structure including an upper fixing plate 3a, a sliding plate 3b, and a lower fixing plate 3c. The sliding plate 3b is connected to the actuator 7, and the sliding plate 3b is connected to the actuator 7. By sliding with the upper fixing plate 3a and the lower fixing plate 3c in close contact with each other, the opening degree of the sliding nozzle 3 is increased and decreased, and the outflow amount of the molten steel 9 from the tundish 1 to the mold 2 is controlled. It is like that.

  In this case, the actuator 7 is actuated by a signal input from a control device 6 such as a PI control device for adjusting the opening degree of the sliding nozzle 3. A molten metal level meter 5 for measuring the position of the molten metal surface 12 in the mold 2 is disposed above the molten metal surface 12 in the mold, and the measurement signal of the molten metal level meter 5 is a control device. 6 is input. That is, the control device 6 continuously inputs a deviation signal between the molten metal level detection signal obtained from the molten metal level meter 5 and a preset molten metal level setting value, and the mold is based on the deviation signal. The opening command of the sliding nozzle 3 is output to the actuator 7 so that the position of the molten steel surface 12 in 2 is constant.

  As shown in FIG. 4, the mold 2 includes a pair of opposed mold long sides 2 a and a pair of opposed mold short sides 2 b that are sandwiched between the mold long sides 2 a and are opposed to each other. When the upper end interval of the mold short side 2b is Wu (m), the lower end interval is Wl (m), and the vertical length of the mold short side 2b is L (m), The short side 2b of the mold is tapered so that the distance between the opposing faces becomes narrower in the casting direction so that the defined taper amount (ΔT) is in the range of 1.1 to 1.3%. ing. The mold 2 is configured such that the mold short side 2b is sandwiched between the mold long sides 2a. Therefore, by disposing the lower end portion to protrude from the upper end portion of the mold short side 2b, the opposite molds are arranged. A taper is provided on the short side 2b. In this case, the taper amounts of the mold short sides 2b on both sides are the same. That is, the taper amount is about ½ of the taper amount (ΔT) defined by the equation (1).

  The mold long side 2a is not tapered, but it is preferable to taper the mold long side 2a from the viewpoint of making the thickness of the solidified shell 10 formed more uniform. The taper amount may be approximately the same as the taper amount (ΔT) of the mold short side 2b. However, the taper of the mold long side 2a is not always necessary for carrying out the present invention.

Here, the reason why the taper amount (ΔT) of the mold short side 2b is in the range of 1.1 to 1.3% will be described. FIG. 5 shows a mold 2 in which the taper amount (ΔT) of the mold short side 2b is in the range of 1.0% to 1.4% under the condition that the casting speed is 2.2 m / min. It is a figure which shows the result of having measured the amount of heat removal. As shown in FIG. 5, when the taper amount (ΔT) of the mold short side 2b was 1.0%, the average overall heat removal amount was 1.66 Gcal / m ² · hr, but the taper amount (ΔT) was It was confirmed that the average overall heat removal rate was increased to 1.85 Gcal / m ² · hr by setting it to 1.1%. That is, by setting the taper amount (ΔT) of the mold short side 2b to 1.1% or more, the contact between the mold long side 2a and the solidified shell 10 of the slab long side is improved, and the taper amount of 1.0% ( It was found that the cooling in the mold can be made more uniform than in the case of ΔT).

  From this result, when the taper amount (ΔT) of the mold short side 2b is 1.0%, particularly between the mold long side 2a and the solidified shell 10 of the slab long side, particularly in the vicinity of the mold short side 2b. It is estimated that an air gap was generated. It was also found that the average overall heat removal is further improved by increasing the taper amount (ΔT) to greater than 1.1%, but the degree of improvement is not so great. Further, when the taper amount (ΔT) of the mold short side 2b is 1.4%, the narrowing is too strong, the wear of the lower end of the mold short side 2b becomes intense, and the solidified shell 10 is seated. It has also been found that the rate of occurrence of breakout due to bending or the seizure between the mold short side 2b and the solidified shell 10 increases.

  Therefore, from these results, the taper amount (ΔT) of the mold short side 2b was determined to be in the range of 1.1 to 1.3% as a condition for uniformizing the cooling in the mold.

  Using the slab continuous casting machine configured as described above, the present invention is carried out as follows. First, molten steel 9 is poured into the tundish 1 from a ladle (not shown), and then the molten steel 9 poured into the tundish 1 is cast through the immersion nozzle 4 while adjusting the flow rate with the sliding nozzle 3. Inject into 2. At that time, a mold powder 13 serving as a heat insulating agent, an antioxidant, a lubricant with the mold 2 and the like is added to the molten steel surface 12 in the mold. The molten steel 9 poured into the mold 2 is cooled by the mold 2 and solidifies at the contact surface with the mold 2 to form a solidified shell 10, and an outer shell is the solidified shell 10 and the inside is an unsolidified portion 11. Is pulled out below the mold 2 by the driving force of the pinch roll while being supported by the slab support roll 8 such as a guide roll and a pinch roll. The position control of the molten steel level 12 is carried out by a level level control device comprising a level level meter 5, a control device 6, an actuator 7, and a sliding nozzle 3.

In this case, as the mold powder 13 to be used, it is preferable to use a mold powder having a basicity (CaO / SiO ₂ ) in the range of 0.85 to 1.00. Here, the reason for using the mold powder 13 having a basicity (CaO / SiO ₂ ) in the range of 0.85 to 1.00 will be described.

  The mold powder 13 added to the molten steel surface 12 is melted by the heat from the unsolidified portion 11, and the melted mold powder flows into the gap between the solidified shell 10 and the mold long side 2a. Similarly, it flows into the gap between the solidified shell 10 and the mold short side 2b. Therefore, the solidified shell 10 is cooled to the mold 2 through the thin film layer of the mold powder 13 that has flowed. The mold powder that has flowed into the gap is cooled by the mold 2 so that the side in contact with the mold wall surface is solidified and the side in contact with the solidified shell 10 is kept in a molten state. It is known that when the molten mold powder is solidified, it is solidified in two states: when it is solidified in a glassy state and when it is crystallized and solidified. It is known that the amount of heat extracted as radiant heat is reduced as compared with the case of solidifying as it is, and the cooling is slow and uniform cooling.

FIG. 6 is a diagram showing the relationship between the basicity (CaO / SiO ₂ ) of the mold powder and the content of caspodyne after solidification. The higher the basicity (CaO / SiO ₂ ), the higher the content of caspidine. . Here, it is known that the higher the content of caspidyne, the higher the crystallinity. In other words, the higher the basicity (CaO / SiO ₂ ) of the mold powder, the slower the cooling, and the cooling in the mold becomes uniform.

Therefore, based on this phenomenon, the basicity (CaO / SiO ₂ ) of the mold powder 13 was changed, and the relationship with the bulging hot water surface fluctuation at that time was examined. As a result, when a mold powder having a basicity (CaO / SiO ₂ ) of 0.78 was used, bulging surface fluctuation occurred frequently, but the basicity (CaO / SiO ₂ ) was 0.85. When mold powder was used, it was found that bulging level fluctuation was greatly reduced.

That is, from this test result, it was found that it is preferable to use a mold powder having a basicity (CaO / SiO ₂ ) of 0.85 or more in order to reduce the fluctuation of the bulging hot water surface. However, the mold powder 13 needs to fulfill other important functions such as a lubrication function in addition to the function that affects the cooling efficiency. If the basicity (CaO / SiO ₂ ) is too high, Since it was found that other functions such as the lubrication function were impaired, the upper limit of basicity (CaO / SiO ₂ ) was set to 1.00. The present inventors have confirmed that other functions of the mold powder are not impaired if the basicity (CaO / SiO ₂ ) of the mold powder 13 is 1.00 or less.

  Further, the casting speed in the steady casting region is preferably 1.5 m / min or more, and more preferably 2.0 m / min or more from the viewpoint of improving the productivity of the continuous casting machine. Further, in the case of low speed casting, since the thickness of the solidified shell 10 is sufficiently increased and the amount of bulging is reduced, the frequency of occurrence of bulging surface level inevitably decreases. Also from this, it is preferable to apply the present invention when the casting speed is 1.5 m / min or more. As the casting speed increases, the fluctuation of the bulging hot water surface becomes more severe. Therefore, the effect of the present invention becomes remarkable particularly in high-speed casting of 2.0 m / min or more. The upper limit of the casting speed need not be specified, but the current maximum speed in a slab continuous casting machine is about 3.5 m / min, and the effect of the present invention can be exhibited even at this casting speed. .

  By continuously casting the molten steel 9 in this way, the cooling in the mold is made uniform to obtain a solidified shell 10 having a uniform thickness, unsteady bulging between rolls of the solidified shell 10 is suppressed, and unsteady bulging is performed. It is possible to suppress bulging level fluctuations in the mold caused by the above. As a result, it is possible to stably produce a high-quality slab free from mold powder with high productivity.

  Hereinafter, the example of this invention in the continuous slab casting machine shown in FIG. 3 is demonstrated with a prior art example. The continuous casting machine used is a vertical bending slab continuous casting machine having a length of 42 m and a vertical part of 2.5 m, and a slab slab of low carbon Al killed steel having a thickness of 238 mm and a width of 1250 mm. Casting was performed at a casting speed of 2 m / min.

Using a mold powder having a basicity (CaO / SiO ₂ ) of 0.78, the taper amount (ΔT) of the mold short side was 1.1% (Invention Example 1) and 1.2% (Invention Example 2). ). Further, when the taper amount (ΔT) of the short side of the mold was 1.1%, a mold powder having a basicity (CaO / SiO ₂ ) of 0.86 was also used (Example 3 of the present invention). For comparison, casting (conventional example) was also performed using a mold powder having a basicity (CaO / SiO ₂ ) of 0.78 with a taper amount (ΔT) of the mold long side of 1.0%.

  During casting, the fluctuation of the molten metal surface is measured by a molten metal surface level meter, and the percentage of the total casting period during which the bulging-type molten metal fluctuation of the molten metal surface fluctuation amount is 10 mm or more occurs is defined as the “rate of occurrence of molten metal fluctuation”. And evaluated. Table 1 shows the results of the investigation of the casting conditions and the occurrence rate of molten metal surface fluctuations.

  As shown in Table 1, the rate of occurrence of molten metal surface fluctuation in the present invention example is 2/3 or less of the conventional example, and in particular, in the case of the present invention example 3 using a mold powder having a high basicity, 1 / It turned out to be around 3. That is, according to the present invention, the fluctuation of the bulging level in the mold caused by unsteady bulging of the solidified shell is suppressed, and a high quality slab free from mold powder can be stably produced with high productivity. Was confirmed.

It is a figure which shows the example of the hot metal surface fluctuation | variation in a casting_mold | template in the continuous casting of steel, and a casting speed. It is a figure which shows typically the relationship between the bulging of a solidification shell, and a molten metal surface fluctuation | variation. It is a schematic side view of the mold periphery of the slab continuous casting machine used in the present invention. It is a schematic perspective view of the casting_mold | template shown in FIG. It is a figure which shows the relationship between the taper amount of a casting_mold | template short side, and the heat removal amount of a casting_mold | template long side. It is a figure which shows the relationship between the basicity of mold powder, and caspidine content.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tundish 2 Mold 2a Mold long side 2b Mold short side 3 Sliding nozzle 4 Immersion nozzle 5 Molten surface level meter 6 Control device 7 Actuator 8 Cast slab support roll 9 Molten steel 10 Solidified shell 11 Unsolidified part 12 Molten steel surface 13 Mold powder

Claims (3)

A method for producing a continuous cast slab by continuously casting a molten steel while suppressing fluctuations in the mold surface caused by unsteady bulging of a solidified shell, and producing a slab slab comprising a pair of opposed long mold sides And a pair of mold short sides opposite to each other, the distance between the upper ends of the opposed mold short sides is Wu, the distance between the lower ends is Wl, and the length of the mold short side in the vertical direction is L as shown in (1) below. Solidified in the mold by continuous casting using a mold with a taper on the short side of the mold so that the taper amount (ΔT) defined by the formula is in the range of 1.1 to 1.3%. A method for producing a continuous cast slab, characterized in that the thickness of the shell is made uniform, thus suppressing fluctuations in the mold surface.
ΔT = (Wu−Wl) × 100 / L ... (1) _2. The continuous cast slab according to claim 1, wherein a mold powder having a basicity (CaO / SiO ₂ ) in the range of 0.85 to 1.00 is added to the surface of the molten steel in the mold. Manufacturing method.   The method for producing a continuous cast slab according to claim 1 or 2, wherein a casting speed of the slab slab is 2.0 m / min or more.

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