JP5710448B2 - Control method of electromagnetic stirring device in mold at the end of casting - Google Patents

Description

  The present invention relates to a method for controlling applied strength at the end of casting in casting using an in-mold electromagnetic stirring device.

  Conventionally, casting using an in-mold electromagnetic stirrer that stirs molten steel in a mold by electromagnetic force has been performed. By stirring the molten steel, bubbles or alumina inclusions trapped at the solidification interface are washed away, improving the quality of the slab, and making the molten steel temperature uniform in the mold and suppressing the decrease in molten steel temperature near the meniscus. It is done. Here, at the end of casting, there is a possibility that inclusions and slag floating on the molten steel surface in the tundish are rolled up and cast. Therefore, in Patent Document 1, at the end of casting, the applied strength (magnetic flux density) is reduced and the stirring force is weakened to prevent inclusions and slag from being caught in the mold.

JP 59-229266 A

  By the way, when inclusions and slag in the tundish flow out into the mold, the cleanliness of the molten steel deteriorates and inclusions and the like are easily trapped at the solidification interface. If inclusions or the like are mixed into the slab without being washed away from the solidification interface, the quality of the slab is degraded. In particular, at the end of casting, inclusions and slag tend to flow out from the tundish into the mold. At this time, if the stirring force is weakened as in Patent Document 1, the effect of cleaning these is weak despite the large amount of inclusions, etc., so that the inclusions taken into the slab etc. Will increase. As a result, the quality of the slab at the end of casting is deteriorated.

  Further, if the stirring force is weakened at the end of casting as in Patent Document 1, a decrease in the molten steel temperature in the vicinity of the meniscus cannot be suppressed, so that the molten steel surface in the mold is easily solidified. As a result, the generation of dickel and the incorporation of bubbles and inclusions in the molten steel occur, leading to a deterioration in the quality of the slab at the end of casting.

  Then, an object of this invention is to provide the method which can improve the quality of the slab at the end of casting.

According to the present invention, in the deceleration region in which the casting speed is reduced after the steady region where the casting speed is constant, the ratio X _t of the applied intensity B _{d in} the deceleration region to the applied strength B _{s in the} steady region is _expressed by the following equation (1). It is the control method of the electromagnetic stirring device in the mold at the end of casting, characterized by satisfying the above.
[(20 / T) × t + 100] ≦ X _t ≦ 180 (1)
However, T is the time from the start of deceleration of the casting speed to the end of casting [min. ]
t is the elapsed time from the start of deceleration of the casting speed [min. ]
X _t is the ratio of the applied intensity B _{d in} the deceleration region to the applied intensity B _s in the steady region at time t [%]

According to the present invention, as the ratio X _t is within a predetermined range, by controlling the applied intensity B _d of the deceleration zone, in casting the end, it is possible to improve the cleaning effect of the solidification interface, the meniscus near The decrease in molten steel temperature can be suppressed. Thereby, since mixing of slag into a slab and uptake | capture of a bubble and an inclusion can be prevented, the quality of the slab at the end of casting can be improved.

  According to the present invention, it is possible to prevent the slag from being mixed into the slab and the introduction of bubbles and inclusions in the molten steel at the end of casting, so that the quality of the slab at the end of casting can be improved.

(A) is a cross-sectional schematic diagram which shows the structure of a part of continuous casting machine of this embodiment, (b) is sectional drawing along the IB-IB line of (a). (A) is a figure which shows the relationship between casting speed and casting time, (b) is a figure which shows the relationship between ratio _Xt and casting time. It is a figure which shows the relationship between ratio _Xt and time ratio t / T. It is a figure which shows experimental conditions (relationship between a casting speed and casting time). It is a figure which shows experimental conditions (plan view of a casting_mold | template). It is a figure which shows an experimental result (Example). It is a figure which shows an experimental result (Example). It is a figure which shows an experimental result (Example). It is a figure which shows an experimental result (Example). It is a figure which shows an experimental result (comparative example). It is a figure which shows an experimental result (comparative example). It is a figure which shows an experimental result (comparative example).

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, the continuous casting machine 100 includes a tundish 1 that accommodates molten steel supplied from a ladle, an immersion nozzle 2 attached to the bottom of the tundish 1, and a lower portion of the immersion nozzle 2. The mold 3 and an in-mold electromagnetic stirring device 4 disposed outside the mold 3 are provided. Further, the mold powder 6 is floating on the molten steel 5 in the mold 3. As shown in FIG.1 (b), the casting_mold | template 3 is formed in the substantially rectangular shape in planar view.

  The in-mold electromagnetic stirring device 4 has a pair of motors 4a and 4b disposed on opposite sides of the mold 3 with respect to each other. As shown in FIG. 1B, the motors 4 a and 4 b are provided along the long side of the mold 3. The molten steel 5 in the mold 3 flows mainly by the electromagnetic force generated by the in-mold electromagnetic stirring device 4 and the discharge flow from the immersion nozzle 2. The arrow shown in FIG.1 (b) has shown the flow (an example) of the molten steel 5. FIG.

  By the way, when the casting speed reaches a predetermined operational speed after the start of casting, the speed is maintained and then decelerated at the end of casting (see FIG. 2A). In the present embodiment, the time when the casting speed is maintained at a predetermined speed is referred to as “steady region s”, and the time when the casting speed is subsequently reduced is referred to as “deceleration region d”. The “deceleration zone d” is from the start of deceleration (at the end of the “steady zone s”) to the end of casting, and starts deceleration when the amount of molten steel in the tundish 1 becomes equal to or less than the specified amount. 2 and 3, the initial casting is omitted.

In the present embodiment, as shown in FIG. 2 (b), in the "deceleration zone d", so that the ratio X _t is within a predetermined range, controls the application intensity B _d in-mold electromagnetic stirring device 4 Then, by increasing the stirring force of the molten steel 5, the effect of cleaning the solidification interface is improved and the temperature drop of the molten steel 5 is suppressed. Here, the ratio X _t, is the ratio of the applied intensity B _d of the reduction zone d with respect to the applied intensity B _s of constant region s. Hereinafter, a method for controlling the application intensity B _{d in} the “deceleration region d” will be described in detail with reference to FIG.

(Lower limit of the ratio _{X t)}
In FIG. 1 (a), when the stirring force of the molten steel 5 in the mold 3 is small, the detergency of the solidification interface is weak, so that inclusions (slag) and bubbles trapped at the solidification interface cannot be sufficiently washed away ( The inclusions and bubbles 8 attached to the solidified shell 7 in FIG. Further, since the amount of heat supplied to the molten steel 5 is small, the surface of the molten steel 5 is easily solidified. Here, the “inclusions” refer to slag flowing out from the ladle into the mold 3, oxides in the molten steel 5, and the like. The “bubbles” are floating from the molten steel 5 and are caused by Ar gas blown from the upper nozzle connected to the upper part of the immersion nozzle 2 or the immersion nozzle 2.

Therefore, "deceleration zone d" in "" ratio X _t of the "applied intensity B _d of the reduction zone d" with respect to the applied intensity B _s "of constant region s" [%] is to satisfy the following equation (A).
[(20 / T) × t + 100] ≦ X _t (A)
Here, T is the time from the start of deceleration to the end of casting (time of the deceleration region d) [min. It is calculated from the amount of molten steel remaining in the tundish.
T is the elapsed time from the start of deceleration [min. And 0 ≦ t ≦ T.
Furthermore, X _t is the time t, is the ratio of the "applied intensity B _d of the reduction zone d" to "applied intensity B _s of constant region s" [%] is represented by the following formula (B).
X _t = (B _d / B _s ) × 100 (B)

In the above formula (A), the lower limit of _{X t (X t = (20} / T) × t + 100) , as shown in FIG. 3, with gradual increase of the ratio _{X t} from the deceleration start to finish casting, during the casting End the ratio X _t in which increased 20% from the deceleration start time of the ratio X _t.

(The upper limit of the ratio _{X t)}
In FIG. 1A, when the stirring force of the molten steel 5 in the mold 3 is too large, the surface of the molten steel greatly fluctuates, and the mold powder 6 on the molten steel 5 is caught in the molten steel 5. Therefore, "deceleration zone d" in "" ratio X _t of the "applied intensity B _d of the reduction zone d" with respect to the applied intensity B _s "of constant region s" [%] is to satisfy the following equation (C).
X _t ≦ 180 (C)

In the above formula (C), the upper limit of _{X t (X t} = 180), as shown in FIG. 3 shows the case where the ratio _{X t} across from deceleration start to the end casting is 180%.

From the above, in the “deceleration region d” at the end of casting, “the ratio X _{t of} “ applied intensity B _d of deceleration region d ”to“ applied intensity B _s of steady region s ”” [%] is _{expressed by the following} equation (1). The application intensity B _d of the deceleration region _d is controlled so as to satisfy (see FIG. 3). In FIG. 3, a region that satisfies the following expression (1) is a region R.
[(20 / T) × t + 100] ≦ X _t ≦ 180 (1)

Here, the operation conditions of this embodiment will be described. Note that the following conditions are examples and can be changed.
Casting speed in the steady region s (V _c shown in FIG. 2 (a))
0.60 [m / min. ] 2.3 [m / min.] ] Below ・ Mold powder
Viscosity: 0.05 Pa · s to 0.24 Pa · s ・ Immersion nozzle
2-hole nozzle with discharge hole angle of 15 ° to 35 °
10 degreeC or more and 30 degrees C or less A molten steel superheat degree is calculated | required from "the molten steel temperature (measurement temperature) in a tundish-solidification temperature". Here, the molten steel temperature (measurement temperature) in the tundish was measured by immersing a batch temperature measuring rod from the molten steel surface to a depth of 100 mm or more and 200 mm or less immediately above the injection hole formed in the bottom of the tundish. Temperature.
-Steel type Carbon content is 0.01 [mass%] or more and 1.05 [mass%] or less Oxygen content is 0.0003 [mass%] or more and 0.0010 [mass%] or less Here, the above-mentioned “oxygen content” "Is the amount of oxygen dissolved in the steel (the amount of free oxygen) and does not include the amount of oxygen in the inclusions. Therefore, the “oxygen content” is different from the total oxygen amount including the free oxygen amount and the oxygen amount in the inclusions.

Moreover, the control method of the in-mold electromagnetic stirring apparatus 4 of this embodiment can be applied to continuous casting using the following continuous casting machine or the like.
・ Slab continuous casting machine capable of casting slabs of (thickness) 230 mm × (width) 800 mm to 1800 mm ・ Bloom continuous casting machine capable of casting bloom of (thickness) 380 mm × (width) 600 mm

As described above, in this embodiment, so that the ratio X _t satisfies the above formula (A), by controlling the applied intensity B _d of the reduction zone d, it can be secured agitation force of the molten steel 5. Thereby, since the washing | cleaning effect of a solidification interface can be improved, the inclusion and bubble which adhered to the solidification interface can be washed away sufficiently. Therefore, these can be prevented from being mixed into the slab. Moreover, since sufficient heat quantity can be supplied to the molten steel 5, the temperature fall of the molten steel 5 of the meniscus vicinity can be suppressed. Thereby, since solidification of the surface of the molten steel 5 can be prevented, it is possible to prevent generation of dickel and intake of bubbles and inclusions in the molten steel.

The prevention, so that the ratio X _t satisfies the above formula (C), by controlling the applied intensity B _d of the reduction zone d, it is possible to suppress the melt surface variations of the molten steel 5, the entrainment of mold powder 6 it can.

Thus, improved in the deceleration range d of the cast end, so as to satisfy the ratio X _t is a (1), by controlling the applied intensity B _d of the reduction zone d, the casting end, the cleaning effect of the solidification interface And the temperature drop of the molten steel 5 in the vicinity of the meniscus can be prevented. Therefore, since inclusions and bubbles can be prevented from being mixed into the slab, the quality of the slab at the end of casting can be improved.

  Next, examples and comparative examples of the present invention will be described.

(Example (Experiment Nos. 1 to 16), Comparative Example (Experiment Nos. 17 to 28))
Whether generation of deckle in the mold of "ratio X _t of the" applied intensity B _d of "deceleration zone d with respect to the applied intensity B _s" of constant region s'"[%] when changing the" deceleration zone d " And the presence or absence of defects in the slab was examined.

Table 1 shows the evaluation results and experimental conditions, as the experimental conditions, shows an example of a ratio X _t at time t. 4 and 5 show the experimental conditions, and FIGS. 6 to 12 show the evaluation results (relationship between the ratio _Xt and the time ratio t / T at the end of casting). Here, “the end of casting” in FIGS. 6 to 12 indicates “deceleration range d”. The “upper limit” in FIG. 10 is the upper limit (X _t = 180) of the formula (1), and the “lower limit” in FIGS. 10 to 12 is the lower limit (X _t = (20 / T) × t + 100 of the formula (1). ). Moreover, in FIGS. 6-12, the casting initial stage and the steady region s are abbreviate | omitted.

  The experimental conditions and evaluation results shown in Table 1 will be described below. In addition, the short side D of the mold upper inner dimension shown in Table 1 corresponds to the thickness of the slab, and the long side W corresponds to the width of the slab (see FIG. 5). Moreover, in the present Example and the comparative example, it operate | moved on the same conditions as the operation conditions (Mold powder, an immersion nozzle, a continuous casting machine, etc.) illustrated by this embodiment.

<減速域ｄの時間Ｔ（減速開始から鋳造終了までの時間）>
減速開始時にタンディッシュ内に残存した溶鋼量から時間Ｔを算出した。本実施例及び比較例では、溶鋼量が５０ｔｏｎ以下になってから減速を開始した。図４に示すＴ_１，Ｔ_２，Ｔ_３，Ｔ_４は、それぞれ、減速パターン１，２，３，４の時間Ｔである。また、図４では、パターン３，４の減速開始時が同時である場合を図示しているが、本実施例及び比較例にはパターン３，４の減速開始時が同時でない場合も含まれる。同様に、図３では、パターン１〜３（４）の減速開始時がそれぞれ異なる場合を図示しているが、本実施例及び比較例にはパターン１〜４の減速開始時が同時である場合も含まれる。
<磁束密度>
鋳型内のメニスカス位置（溶鋼表面）で測定した複数の磁束密度の平均磁束密度を算出した。図５に示すように、鋳型の対向する２つの長辺からそれぞれ１０ｍｍ離れた位置において、鋳型の一方の短辺から１／４Ｗ，１／２Ｗ，３／４Ｗだけ離れた位置（合計６箇所）で磁束密度を測定した。表１には、これらの平均磁束密度を示している。 [Experimental conditions]
<Casting speed in deceleration area d>
The casting speed in the deceleration region d was changed in the following four patterns shown in FIG.
Pattern 1: The casting speed is reduced stepwise three times in the deceleration range d.
Pattern 2: The casting speed is decelerated four times stepwise in the deceleration region d.
Pattern 3: The casting speed is decelerated five times stepwise in the deceleration region d.
Pattern 4: The casting speed is gradually reduced over the entire deceleration area d.
In the column of “Deceleration pattern” in Table 1, the pattern numbers shown in FIG. 4 are shown. In FIG. 4, the casting speed in the deceleration region d is mainly shown, and a part of the casting initial stage and the steady region s is omitted.
The column of “Deceleration (average deceleration amount)” in Table 1 shows the average deceleration amount per unit time in the deceleration range d (see the following formula).

<Time T of deceleration area d (time from the start of deceleration to the end of casting)>
Time T was calculated from the amount of molten steel remaining in the tundish at the start of deceleration. In this example and comparative example, deceleration was started after the amount of molten steel became 50 ton or less. T ₁ , T ₂ , T ₃ , and T ₄ shown in FIG. 4 are times T of the deceleration patterns ₁ , ₂ , ₃ , and ₄ , respectively. FIG. 4 illustrates the case where the deceleration start times of the patterns 3 and 4 are simultaneous, but the present embodiment and the comparative example also include the case where the deceleration start times of the patterns 3 and 4 are not simultaneous. Similarly, FIG. 3 illustrates a case where the deceleration start times of patterns 1 to 3 (4) are different from each other, but in this embodiment and the comparative example, the deceleration start times of patterns 1 to 4 are simultaneous. Is also included.
<Magnetic flux density>
An average magnetic flux density of a plurality of magnetic flux densities measured at the meniscus position (molten steel surface) in the mold was calculated. As shown in FIG. 5, at a position 10 mm away from two opposing long sides of the mold, positions separated by 1/4 W, 1/2 W, 3/4 W from one short side of the mold (total of 6 locations) The magnetic flux density was measured. Table 1 shows these average magnetic flux densities.

[Evaluation results]
<Generate Dickel>
When the deckle is generated on the molten steel, when the detection rod is inserted into the molten steel in the mold, a reaction force (load) due to the deckle acts on the detection rod. Therefore, in this embodiment and the comparative example, when the detection rod made of iron wire is inserted into the molten steel in the mold in the deceleration region d and the detection rod can be inserted into the molten steel without resistance, deckle is generated on the molten steel. In other words, “◯” is shown in Tables 1 and 2. Here, the time when the detection rod can be inserted into the molten steel without resistance is when the reaction force (load) by the deckle is less than 0.2 kgf. On the other hand, when the detection rod was inserted into the molten steel in the mold and received a load of 0.2 kgf or more, it was evaluated that Dickel was generated on the molten steel, and Tables 1 and 2 indicate “x”. . In the above description, the insertion position of the detection rod is set to a position separated by ½ W from the short side of the mold. Note that the above-described evaluation of the generation of the deckle is performed with reference to a method using the deckle generation state detection apparatus described in JP-A-2-41740.
<Occurrence of epidermal defect>
The presence or absence of pinhole defects in the slab surface layer, defects due to mold powder, inclusions, etc. was examined. The surface of the slab was surface-treated (cared for) by gas cutting (scarf), and when no defects having a depth of 1 mm or more were generated from the surface of the slab, it was evaluated that no product defect occurred. “○” is shown. On the other hand, when a defect having a depth of 1 mm or more has occurred from the surface of the slab, it is evaluated that a product defect such as a baldness occurs in the subsequent rolling process due to the defect, and “x” is shown in Table 1. (Source: Steel Times (incorporating IRON & STEEL), APRIL 1989, VOL217, NO 4, p. 180, FIG. 1).

From Table 1 and FIGS. 5-11, in Example (experiment number 1-16), ratio _Xt exists in the range of the area | region R which satisfy | fills (1) Formula in the whole deceleration area | region d (refer FIG. 3). At the same time, it was found that it was possible to prevent the generation of deckle and the occurrence of product defects. On the other hand, in Comparative Example (Test No. 17 to 28), the ratio X _t deceleration region d, (1) is outside the range of the region R does not satisfy the equation, it found that the generation of product failure of deckle occurs It was.

In Experiment numbers 17 and 18 of the comparative example, greater than the ratio _{X t} is the upper limit of the (1) formula _{(X t> 180 [%]} ), for agitation force of the molten steel was large, the mold powder on the molten steel caught in the molten steel It is thought that the epidermal defect occurred.

Further, in Experiment No. 19 to 28 of the comparative example, the ratio Xt is (1) may formulas smaller than the lower limit of _{(X t <(20 / T} ) × t + 100), stirring force of molten steel was small. For this reason, it is considered that the decrease in the molten steel temperature in the vicinity of the meniscus could not be suppressed, and Dickel was generated. Further, it was considered that inclusions and bubbles adhering to the solidification interface could not be sufficiently washed away, and inclusions and bubbles were trapped in the solidification shell, resulting in epidermal defects.

Here, the lower limit of the ratio X _t, is described by comparing the Test No. 1 (Example) and Experiment No. 19 (comparative example).

In Experiment No. 1, gradually increasing the ratio _{X t} from the deceleration start to finish casting, the ratio _{X t} during the casting completion was increased 20% than the ratio _{X t} at the start of casting _{(X t = (20 / T} ) × t + 100 [%]), the effect of the present invention was obtained. In contrast, in Experiment No. 19, gradually increasing the ratio X _t from the deceleration start to finish casting, the ratio X _t during the casting completion was increased by 10% than the ratio X _t at the start of casting (X t ₌ ( 10 / T) × t + 100 [%]), the effect of the present invention was not obtained. Therefore, by setting the lower limit of the ratio _{X t} and _{X t = (20 / T)} × t + 100, it was found that the effect of the present invention can be obtained.

Next, the upper limit of the ratio X _t, is described by comparing the experimental number 16 (Example) and Experiment No. 18 (comparative example).

In Experiment No. 16, when the ratio _Xt was set to 180 [%] in the entire deceleration range d ( _Xt = 180), the effect of the present invention was obtained. On the other hand, in Experiment No. 18, when the ratio X _t was set to 186 [%] in the entire deceleration range d (X _t = 186), the effect of the present invention was not obtained. Therefore, by setting the upper limit of the ratio X _t and 180 [%], it was found that the effect of the present invention can be obtained.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above-described embodiments and examples, and various modifications are possible as long as they are described in the claims.

For example, FIG. 2B shows an example of the relationship between the ratio _Xt and the casting time, but the relationship between the ratio _Xt and the casting time can be changed as long as the ratio _Xt satisfies the expression (1). . Further, in the present embodiment and the embodiment (FIG. 2 (b) and FIG. 6-12), across the velocity reduction zone d, but when and ratios X _t the ratio X _t is increased been described is a constant, The ratio _Xt is not limited to the case described above. For example, the ratio _Xt may be increased to the middle of the deceleration range d, and then the ratio _Xt may be decreased. Alternatively, the ratio _Xt may be kept constant until the middle of the deceleration range d, and then the ratio _Xt may be decreased.

  2A and 4 show a case where the casting speed is gradually reduced over the entire deceleration area d, and FIG. 4 shows a case where the casting speed is reduced stepwise 3 to 5 times in the deceleration area d. However, the casting speed in the deceleration area d is not limited to that shown in FIGS. For example, the casting speed may be gradually reduced to the middle of the deceleration region d, and then the casting speed may be made constant. Further, in the deceleration area d, the casting speed may be reduced only once or twice stepwise.

Furthermore, the casting speed and the applied intensity of the casting speed of the casting early and applying strength and, constant region s can be changed as long as it meets X _t deceleration region d is the (1) formula.

  In addition, the method for controlling the electromagnetic stirring device in the mold according to the present invention is not limited to the shape of the slab and the steel type, but can be applied to casting of various shapes of slab (slab, bloom, billet, etc.) and various steel types. Can do.

  If the present invention is used, the quality of the slab at the end of casting can be improved.

DESCRIPTION OF SYMBOLS 1 Tundish 2 Immersion nozzle 3 Mold 4 Electromagnetic stirring apparatus 4a, 4b Motor 5 Molten steel 6 Mold powder 7 Solidified shell d Deceleration zone s Steady zone

Claims (1)

In the deceleration area where the casting speed is reduced after the steady area where the casting speed is constant,
The ratio X _t of the applied intensity B _d of the reduction zone for applying the intensity B _s of the constant region is characterized by satisfying the following formula (1), the control method in the mold electromagnetic stirrer device in the cast end.
[(20 / T) × t + 100] ≦ X _t ≦ 180 (1)
However, T is the time from the start of deceleration of the casting speed to the end of casting [min. ]
t is the elapsed time from the start of deceleration of the casting speed [min. ]
X _t is the ratio of the applied intensity B _{d in} the deceleration region to the applied intensity B _s in the steady region at time t [%]

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