JP5283881B2 - Method for continuous casting of steel characterized by raising and lowering the surface level - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a continuous casting method for a steel having characteristics in the elevation of a molten metal surface level capable of obtaining high productivity. <P>SOLUTION: In a state where the lower edge of an immersion nozzle 2 is immersed into a molten steel within a die 1, the molten metal is poured into the die via the immersion nozzle. When the molten metal surface level of the molten metal within the die is ascended or descended, the ascent velocity Vup [mm/sec] and descent velocity Vdown [mm/sec] of the molten metal surface level conform to the following expressions (1) and (2), respectively: 0&lt;Vup [mm/sec]&le;0.20...(1); and 0&lt;Vdown [mm/sec]&le;0.25...(2). <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a continuous casting method of steel, and more particularly to elevation of a molten metal level.

  In continuous casting of steel in which molten steel is poured into a mold through the immersion nozzle in a state where the lower end of the immersion nozzle is immersed in the molten steel in the mold, for example, as in Patent Document 1, “(Immersion nozzle 3 Change the position of the immersion depth h), and raise or lower the level of the molten steel in the mold (usually, there is a molten or unmolten mold powder above this level). doing. This is because the immersion damage of the immersion nozzle caused by the contact with the molten mold powder (hereinafter referred to as the molten mold powder) is dispersed in the longitudinal direction of the immersion nozzle, so that one immersion nozzle can last longer. is there.

Japanese Patent No. 3860668 (see paragraph number 0011)

  By the way, in general, the thickness of the layer of the molten mold powder is about 5 to 20 [mm]. No more than 20 [mm] is sufficient at most, and there has been annoyance in operation, and no one has conventionally managed the speed of change or elevating. On the other hand, securing higher productivity is required every day.

  This invention is made | formed in view of such various points, The main objective is to provide the continuous casting method of steel from which high productivity is obtained.

Means and effects for solving the problems

  The problems to be solved by the present invention are as described above, and the inventor of the present invention has made the above-mentioned lifting / lowering speed (hereinafter referred to as the "water surface level raising / lowering level") that no one has managed after extensive research. This “rising / lowering speed of the molten metal level” includes “a rising speed Vup [mm / sec] of the molten metal level” and “a descending speed Vdown [mm / sec] of the molten metal level”. In the following, the technical significance of the present invention will be introduced in detail: FIGS.1 to 3 are diagrams for explaining various problems associated with raising and lowering the molten metal surface level. 4 corresponds to a cross-sectional view taken along line 1-1 in Fig. 4. Fig. 1 shows the state in the mold before the elevation of the molten metal level, and Fig. 2 shows the state in the mold after the elevation of the molten metal level. FIG. 3 schematically shows the inside of the mold after the molten metal level is lowered.

  First, please refer to FIG. As shown in the figure, there are three mold powders in the mold at the same time. (1) The first is an unmelted mold powder. This unmelted mold powder (hereinafter referred to as “unmelted mold powder”) is a state in which the powdered mold powder supplied from above the mold by a known powder feeder is not yet melted. The surface is distributed with a predetermined thickness in a plane substantially parallel to the hot water surface. (2) The second is the above-described molten mold powder. The molten mold powder is distributed in a film shape so as to wrap the molten steel or solidified shell in the mold. (3) The third is a fixed mold powder. In this fixed mold powder (hereinafter referred to as a fixed mold powder), the molten mold powder (also referred to as a mold powder film) that wraps the solidified shell formed in the mold from the outside is the inner wall surface of the mold. Is formed by being solidified by contact with the inner wall surface and fixed to the inner wall surface. Due to its nature, a protrusion p (rim) projecting toward the immersion nozzle between the unmelted mold powder and the molten mold powder. Also formed).

  In the state of FIG. 1, it can be estimated that when the hot water level is raised, the state shown in FIG. 2 is obtained. That is, the level at which the solidified shell begins to grow increases as the molten metal level rises, but for a short time, the fixed mold powder is fixed to the space while maintaining the shape immediately before the molten metal level rises. Will remain. Therefore, there is a possibility that the protrusion p directly contacts the outer surface of the solidified shell that has started to grow near the molten metal surface level without passing through the molten mold powder, thereby causing the occurrence of throat or vertical split. These blades and vertical splits cause breakage of the solidified shell and cause breakout.

  Moreover, it can be estimated that when the hot water level is lowered in the state of FIG. 1, the state shown in FIG. 3 is obtained. That is, the boundary between the unmelted mold powder and the molten mold powder, which has been stable with the protrusion p as a boundary, moves as the molten metal level decreases, so that the gap between the solidified shell and the fixed mold powder is reduced. There is a possibility that the inlet of the molten mold powder will be disturbed and the thickness of the molten mold powder covering the solidified shell in the form of a film will be uneven or partly missing, and there will be a risk of breaking or vertical splitting. .

  The inventors of the present invention have found that the above-mentioned problems associated with raising and lowering the molten metal level are sufficient for the time required for the fixed mold powder to deform into the steady state shape shown in FIG. We thought that it might be caused by not being secured. Next, means for solving this problem and effects thereof will be described.

According to the first aspect of the present invention, the mold powder is used, and the lower end of the immersion nozzle is immersed in the molten steel in the mold, and the molten steel is poured into the mold through the immersion nozzle. Continuous casting is performed by the following method. That is, when raising and lowering the molten steel level in the mold during continuous casting, the rising speed Vup [mm / sec] and the descending speed Vdown [mm / sec] of the molten steel level are expressed by the following equations (1) and ( Follow 2).

  According to this, since the quality of the slab surface required in HCR or HDR is ensured by a state of no care or simple care after casting, high productivity can be obtained.

The continuous casting of the steel is preferably performed by the following method. That is, even without least upon lifting the molten metal surface level of the molten steel in the mold, the base of C / S and the content of Na ₂ O Na ₂ O of mold powder [wt%], the solidification temperature Ts [° C.] the following formula Follow (3).

  According to this, since the quality of the slab surface required in HCR and HDR is ensured without care after casting, extremely high productivity can be obtained.

  Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 4 is a schematic view of a continuous casting machine. First, based on this figure, the structure and operation | movement of the continuous casting machine 100 are demonstrated easily as an example.

Continuous casting machine 100 cuts molten steel to be poured into mold 1 for forming a solidified shell of a predetermined shape and molten steel held in a tundish (not shown) to mold 1 and shuts off from the atmosphere. In addition, an immersion nozzle 2 for pouring while controlling the flow rate and flow, and a plurality of roll pairs 3, 3,... Arranged in parallel along the casting path Q from directly below the mold 1 are provided. In the present embodiment, the casting path Q is provided in order from the upstream side thereof, a vertical path portion extending in a substantially vertical direction, an arc path portion connected to the vertical path portion and extending in an arc shape, and further provided on the downstream side thereof. The horizontal path portion extends in the horizontal direction. The slab is bent along the path on the entrance side of the arc path part and is corrected to a horizontal state in the arc path part or on the exit side of the arc path part.
Although the above description relates to a general vertical bending type continuous casting machine, the present embodiment is not limited to the above continuous casting machine, and the same applies to a bending type continuous casting machine and a vertical type continuous casting machine. To be done.

  Further, each of the roll pairs 3, 3,.

  Further, upstream of the casting path Q, cooling sprays 4, 4... Spraying cooling water at a predetermined flow rate on the solidified shell formed in the mold 1 and pulled out from the mold 1 are appropriately used. Provided. In general, the mold 1 is referred to as a primary cooling zone, and in this sense, a path portion in which the cooling sprays 4, 4,... Are arranged is referred to as a secondary cooling zone.

  The solidified shell drawn out from the mold 1 and transported along the casting path Q is further cooled and contracted by natural heat dissipation, the cooling sprays 4, 4. Accordingly, the roll gap [mm] of the above-described roll pairs 3, 3... Is generally set so as to gradually become narrower as it proceeds to the downstream side of the casting path Q.

  With the above configuration, when starting continuous casting of a slab slab, a dummy bar (not shown) is inserted into the casting path Q in advance before pouring molten steel into the mold 1 and the immersion nozzle 2 is used. Then, the molten steel starts to be poured into the mold 1 at a predetermined flow rate, and the dummy bar is pulled out downstream at a predetermined speed. The dummy bar is collected by an appropriate means when a predetermined meniscus distance is reached. Thus, the slab slab is continuously cast.

Next, general operating conditions of the continuous casting machine 100 will be briefly introduced.
-The mold width W [mm] is 600-2400.
-Mold thickness D [mm] shall be 200-300.
・ Mold height H [mm] shall be 800-1200.
-The casting speed Vc [m / min] is 0.5 to 2.5.
• The molten steel superheat degree ΔT [° C.] is 10 to 45.
-The specific water amount Wt [L / kgSteel] shall be 0.2-5.
-The electromagnetic stirring intensity M-EMS [gauss] in a mold shall be 0-1200.
-Molten steel composition is based on an agreement between the parties. Typical components are C, Si, and Mn. To this, Cr, Mo or the like is appropriately added. In general, P and S are adjusted to be as small as possible, but may be added depending on the use of the steel material. Contains other inevitable impurities.

Here, each term is briefly explained.
The mold width W [mm] and the mold thickness D [mm] are considered at the upper end of the mold 1.
The casting speed Vc [m / min] is a drawing speed of the slab, and is considered as a peripheral speed of any one of the plurality of roll pairs 3.
The molten steel superheat degree ΔT [° C.] is an index of the temperature of the molten steel poured into the mold 1. Details are described at the end of this specification.
The meniscus distance M [m] means a distance [m] that starts with the molten steel surface (meniscus) in the mold 1 and is considered along the casting path Q.
The specific water amount Wt [L / kgSteel] means the volume of cooling water used for 1 kg of steel. This cooling water is sprayed / sprayed on the slab in the secondary cooling zone.
In-mold electromagnetic stirring strength M-EMS [gauss] is an index of the strength of the magnetic field that is applied to stir the molten steel in the mold 1. Details are described at the end of this specification.

  Next, specific operating conditions of the continuous casting machine 100 according to the present embodiment will be described. In the continuous casting of steel according to the present embodiment, as described above, the molten steel is poured into the mold 1 through the immersion nozzle 2 in a state where the lower end of the immersion nozzle 2 is immersed in the molten steel in the mold 1. Is. When the molten steel level in the mold 1 is raised and lowered, the rising speed Vup [mm / sec] and the descending speed Vdown [mm / sec] of the molten steel level are in accordance with the following formulas (1) and (2), respectively. I will do it.

  More specifically, it may be arbitrarily set as follows. (1) It is common to use a material with improved resistance to melting (for example, ZrO-C brick) at the part of the immersion nozzle where the molten mold powder comes into contact. Measure the erosion rate (mm / min.) Of the corresponding part in advance, and at the time interval (min.) Where the erosion amount of this material part (eg ZrO-C) decreases by about 50% of the total thickness. Change the hot water surface. For example, if the thickness of ZrO-C is 20 mm and the pre-measured erosion rate is 0.08 mm / min., The maximum time is 125 min. And the change is made within that range. Please refer to FIG. 1 because the outer peripheral surface of the immersion nozzle 2 is melted by contact with the molten mold powder. (2) It is arbitrary whether to select ascending or descending of the elevation of the molten steel level in the mold 1. (3) The change width [mm] of the molten steel surface level of the molten steel in the mold 1 is from the site where the molten mold powder has already melted while considering that the layer thickness [mm] of the molten mold powder is 15. For the time being, it is generally preferable to set it to 20 to 30 so as to be deviated in any of the vertical directions.

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

  First, an index used for evaluation of each confirmation test will be described.

<Noromi>
“Noromi” means a depression on the surface of a slab generated by a lump of mold powder. Please refer to FIG. FIG. 5 is a graph showing the relationship between the percentage of blades before scarfing and the percentage of blades after scarfing. “Norokami number ratio npa [pieces / m ² ]” means an anti-reference plane of a so-called primary cutting slab obtained by cutting a slab cast by the continuous casting machine 100, for example, every 5.5 to 12.5 [m] (described above) Value obtained by dividing the number of blades confirmed by visual inspection of the upper surface of the horizontal path portion in the cold (approximately 20 [° C]) by the area [m ² ] of the anti-reference surface. It is. In this figure, “scarfing” means scarfing performed at a depth of 1.5 [mm] with respect to the anti-reference surface. According to this figure, it can be seen that if the number ratio npa [pieces / m ² ] before scarfing is 0.008 or less, the number ratio npa [pieces / m ² ] can be set to 0 by scarfing. From this, first, the evaluation of “Norokami” is “O” when the Norokami count rate npa [pieces / m ² ] before scarfing is 0, and then, When m ² ] satisfies 0 <npa ≦ 0.008, the evaluation for “Noromi” is “△”, and when the percentage of noro [number / m ² ] before scarf satisfies npa> 0.008, Evaluation was set to "x".

If the evaluation for “Noromi” is “○”, the quality related to “Noromi” among the quality required for HCR and HDR will be secured without carrying out scarfing. Productivity can be improved. If the evaluation for “Norokami” is “△”, among the quality required for HCR and HDR, “Norokami” related quality is once scarfed at a depth of 1.5 mm per surface. Since it is ensured only by carrying out, it can be said that the productivity is also good in this case. However, in this case, there is a slight yield loss and variable cost associated with the implementation of scarfing. If the evaluation for “Norokami” is “x”, it may not be able to be completely eliminated by performing scarfing once at a depth of 1.5 mm per surface (see FIG. 5). For this reason, careful inspection and care are required after scarfing, which further increases yield loss and scarfing fluctuation costs, and makes it necessary to use a cold piece for inspection and care, making HCR and HDR impossible. Furthermore, as can be seen from FIG. 5, when the blade ratio npa [pieces / m ² ] exceeds 0.02, the blade that appears inward from the slab surface may appear. If this is the case, it takes a lot of labor to care for, so the product collection is effectively given up.

<Vertical Split>
See Table 1 below. Table 1 is a table showing the relationship between the vertical length before scarfing and the vertical length after scarfing. “Vertical length [mm]” means an anti-reference plane of a so-called primary cutting slab obtained by cutting a slab cast by the continuous casting machine 100, for example, every 5.5 to 12.5 [m] (the horizontal path described above) This is the length [mm] of the vertical division that can be confirmed when the upper surface of the part is visually confirmed with cold (approximately 20 [° C.]). In this table, “scarfing” means scarfing performed at a depth of 1.5 mm with respect to the anti-reference plane. According to this table, it can be seen that when the length [mm] before scarfing is 200 or less, the length [mm] can be reduced to 0 by scarfing. From this, first, when there was no vertical division before scarfing, the evaluation for “vertical division” was set to “○”, and then when the vertical division length [mm] before scarfing was 200 or less, “vertical division” The evaluation for “wari” was set as “Δ”, and when the vertical split length [mm] before scarfing exceeded 200, the evaluation for “vertical split” was set as “x”.

  If the evaluation for "vertical split" is "○", the quality related to "vertical split" among the quality required for HCR and HDR is ensured without carrying out scarfing. Can improve productivity. If the evaluation for “Vertical Split” is “△”, the quality related to “Vertical Split” among the quality required for HCR and HDR is scarfed at a depth of 1.5 mm per surface. In this case, it can be said that the productivity is good because it is ensured only once. However, in this case, there is a slight yield loss and variable cost associated with the implementation of scarfing. If the evaluation for “vertical split” is “×”, vertical split may not be completely eliminated by performing scarfing once at a depth of 1.5 [mm] per face (Table 1 below). reference). For this reason, careful inspection and care are required after scarfing, which further increases yield loss and scarfing fluctuation costs, and makes it necessary to use a cold piece for inspection and care, making HCR and HDR impossible. Furthermore, if the crack depth of the vertical split is deep (experience has a relative relationship between the length of the vertical split and the depth of the vertical split), it takes a lot of labor for maintenance, so product collection is virtually I will give up.

  Next, test conditions common to each confirmation test will be described. The steel types are ultra-low carbon steel, low carbon steel and medium carbon steel with C content C [wt%] of 0.0012 to 0.25. The casting speed Vc [m / min] is 1.3 to 2.2.

  Next, test conditions and test results of each confirmation test are shown in Tables 2 and 3 below, and the types of mold powders indicated by “type” in Tables 2 and 3 are shown in detail in Table 4. Table 2 below relates to the “water surface level rising speed Vup [mm / sec]”, and Table 3 below relates to the “water surface level lowering speed Vdown [mm / sec]”. In Table 2 and Table 3 below, “ΔH mm” means the change level of the molten steel level in the mold 1 and “Δt sec” means the time spent for changing the molten metal level. ”Means“ ○ ”when both“ Norokami ”and“ Vertical Split ”were evaluated as“ O ”, and at least one of the evaluations regarding“ Norokami ”or“ Vertical Split ”was“ X ”. When it was, it was set as “x” and the others were set as “Δ”. In Table 4 below, each mold powder contains components other than those specified (for example, C and inevitably mixed oxides), and the column title “C / S” means so-called basicity. The column title “Ts ° C.” means the solidification temperature of each mold powder (also referred to as crystallization temperature or breakpoint). As the solidification temperature Ts [° C.], an inflection point at which the temperature is continuously lowered from a completely melted state and the viscosity rapidly increases is adopted. Please refer to “Iron and Steel, Vol.73, No.4, S157 (1987.03), Development of Practical Machine for Vibrating Piece Type CC Powder Viscometer” for detailed measurement principle and measurement method. Here, as an example, Test No. 6 described in Table 2 will be outlined. In the confirmation test of Test No. 6, at any time during casting using the mold powder indicated by “E” in Table 4, the change level ΔH [mm] of the molten metal level is set to 30, and The amount of time Δt [sec] spent for the change is set to 300, the level of the molten metal is raised, and “Norokami” and “Vertical split” are applied to the primary cutting slab including the solidified shell existing near the surface of the molten metal at the time of changing Is evaluated.

  As described above, in the above embodiment, in the state where the lower end of the immersion nozzle 2 is immersed in the molten steel in the mold 1, the molten steel is poured into the mold 1 through the immersion nozzle 2, and the continuous casting of steel is The following method is used. That is, when the molten steel level in the mold 1 is raised and lowered, the rising speed Vup [mm / sec] and the descending speed Vdown [mm / sec] of the molten steel level follow the following formulas (1) and (2), respectively. I will do it.

  According to this, the quality required for HCR and HDR can be ensured with no care after casting or only by simple care (see overall evaluation = “Δ”), and high productivity can be obtained.

  Next, a second embodiment of the present invention will be described. Here, the description will focus on the differences of the present embodiment from the first embodiment.

In the first embodiment, the mold powder used during continuous casting is arbitrarily selected from those listed in Table 4, for example. In contrast, in the present embodiment, at least when raising or lowering the molten steel surface level in the mold 1, the basicity C / S of the mold powder and the Na ₂ O content Na ₂ O [wt%], the solidification temperature Ts [° C.] follows the following formula (3).

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

  First, an index used for evaluation of each confirmation test will be described.

<Noromi>
Since it is the same as the above-mentioned index, its description is omitted.

<Vertical Split>
Since it is the same as the above-mentioned index, its description is omitted.

  Next, test conditions common to each confirmation test will be described. The steel types are ultra-low carbon steel, low carbon steel and medium carbon steel with C content C [wt%] of 0.0012 to 0.25. The casting speed Vc [m / min] is 1.3 to 2.2.

Next, test conditions and test results of each confirmation test are shown in Tables 5 and 6 below. Table 5 below relates to the “water surface level rising speed Vup [mm / sec]” side, and Table 6 below relates to the “water surface level lowering speed Vdown [mm / sec]” side. In Table 5 below, in the confirmation tests of Test Nos. 32 to 54, as the rising speed Vup [mm / sec] of the molten metal level, the rising speed Vup [mm / sec] of the molten metal level shown in the above formula (1) The maximum value in the range (the most severe condition) is adopted. In the confirmation test of test Nos. 55 to 59 in Table 6 below, the rising speed Vup [mm / sec] As a result, an intermediate value in the range of the rising speed Vup [mm / sec] of the molten metal surface level shown in the above equation (1) (slightly loose condition) is adopted. Similarly, in the confirmation test shown as Test Nos. 60 to 73 in Table 6 below, the molten metal level lowering speed Vdown shown in the above formula (2) is used as the molten metal level lowering speed Vdown [mm / sec]. The maximum value in the range of [mm / sec] (the one with the strictest conditions) is adopted. In the confirmation test of test Nos. 74 to 79 in Table 6 below, the lowering speed Vdown of the molten metal level is confirmed. As [mm / sec], an intermediate value (with a slightly loose condition) in the range of the descent speed Vdown [mm / sec] of the molten metal surface level shown in the above equation (2) is adopted. In Tables 5 and 6 below, the column titles “C / S” through “Li ₂ O wt%” relate to the components and basicity of the mold powder and the solidification temperature used in each confirmation test, and the column title “MgO wt%”. And in the columns indicated by “BaO wt%”, “B ₂ O ₃ wt%”, “Li ₂ O wt%”, measure only when it is expected to be detected, to the extent that it will not be detected. However, if it is expected that it is unavoidably mixed, the measurement was omitted for economic reasons.

As described above, in the above embodiment, the continuous casting method of steel is further performed by the following method. That is, a mold powder is used during continuous casting. At least when raising and lowering the molten steel level in the mold 1, the basicity C / S of the mold powder and the Na ₂ O content Na ₂ O [wt%] and the solidification temperature Ts [° C.] are expressed by the following formula (3) To follow.

  According to this, the quality required for HCR and HDR is ensured without care after casting (see overall evaluation = “◯”), and extremely high productivity can be obtained.

The basicity C / S of the mold powder is preferably 0.8 or more for the following reason. In other words, except for some ultra-low carbon steels, there is a possibility of slab vertical cracks due to strong cooling in the mold, so crystals such as cuspidyne are precipitated from the molten mold powder to reduce the heat removal rate. It is necessary to let For this reason, it is necessary to increase the CaO concentration in the powder to some extent. Further, the inventor of the present invention indicated that the basicity C / S and Na ₂ O content Na ₂ O [wt%] of the mold powder and the solidification temperature Ts [° C.] strongly influence the formation of crystals in the molten mold powder. It is considered that the generation of the protrusion p described above can be suppressed by strictly managing these values within a predetermined range.

  The following are reference materials.

<Measurement method of hot water level>
In order to measure the level of molten steel in the mold 1, for example, a known eddy current level meter is suitable.

<How to change the surface level>
The change in the molten steel level in the mold 1 is generally due to a temporary increase or decrease in throughput from the immersion nozzle 2.

<Molten steel superheat degree ΔT [° C]>
Definition: A measure of the temperature of the molten steel poured into the mold.
(1) “Measurement time” is “Starting casting using a tundish that has been sufficiently heated in advance, the casting speed is constant at the same mold width, and the volume of molten steel in the tundish is constant. The time at which a steady state is reached when the pouring amount rate from the ladle to the tundish (ton / min.) And the pouring rate from the tundish to the mold (ton / min.) Substantially coincide.
(2) “Measurement points” are as follows. That is, the “horizontal position” is the axis of the immersion nozzle provided on the bottom surface of the tundish, and the “vertical position” is 100 mm deep with reference to the molten steel surface held in the tundish.
(3) The “measuring instrument” shall use a consumable thermocouple. As described above, since the consumable thermocouple is immersed in a point having a depth of 100 mm, a configuration in which the consumable thermocouple is attached to the tip of a suitably prepared rod is suitable.
(4) Compare the liquidus temperature determined solely by the molten steel component of the molten steel from the temperature of the molten steel measured according to the above “measurement time”, “measurement point”, and “measuring instrument”. The above-described molten steel superheat degree ΔT [° C.] is obtained as the remainder obtained by subtracting the latter from the former.
(5) From various viewpoints, the molten steel superheat degree ΔT [° C.] is preferably 10 to 45.

<Electromagnetic stirring intensity in mold M-EMS [gauss]>
Definition: A measure of the strength of the magnetic field that is applied to stir the molten steel in the mold 1.
(1) The “measurement time” is arbitrary.
(2) “Measurement points” are as follows. That is, the “horizontal position” is (i) the center in the mold width direction, (ii) 15 [mm] from the mold inner wall surface to the center in the mold thickness direction, and (iii) in the mold height direction. Align with the coil center of the electromagnetic coil embedded in the mold.
(3) Use an appropriate gauss meter as the “measuring instrument”.
(4) Measure multiple times according to the above “Measurement time”, “Measurement point”, and “Measurement instrument”. The above-described in-mold electromagnetic stirring intensity M-EMS [gauss] is obtained by averaging the plurality of measured values.
(5) From various viewpoints, the above-mentioned electromagnetic stirring intensity M-EMS [gauss] in the mold is preferably 0 to 1000, and the magnetic field frequency [Hz] ("magnetic field frequency applied to the molten steel in the mold""Means the number of times the current conducted to the electromagnetic coil changes direction per second.) Is preferably 1 to 5, and generally 2 is adopted as the frequency [Hz] of this magnetic field.

Illustration for explaining various problems associated with raising and lowering the hot water level Similar to FIG. Similar to FIG. Schematic diagram of continuous casting machine A graph showing the relationship between the percentage of blades before scarfing and the percentage of blades after scarfing

Explanation of symbols

1 Mold
2 Immersion nozzle
100 continuous casting machine
p protrusion
Vup Raising speed of hot water level [mm / sec]
Vdown Descent speed of hot water level [mm / sec]

Claims (2)

In a continuous casting method of steel, in which molten powder is poured into the mold through the immersion nozzle in a state where the lower end of the immersion nozzle is immersed in the molten steel in the mold using a mold powder ,
When raising and lowering the molten steel level in the mold during continuous casting, the rising speed Vup [mm / sec] and the descending speed Vdown [mm / sec] of the molten steel level are expressed by the following equations (1) and (2), respectively. To comply with the
A continuous casting method for steel characterized by the above.

In the continuous casting method of the steel according to claim 1 ,
Even without least upon lifting the molten metal surface level of the molten steel in the mold is, ₂ O content basicity C / S and Na of mold powder Na ₂ O [wt%], the solidification temperature Ts [° C.] the following formula (3 )
A continuous casting method for steel characterized by the above.

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