JP5272720B2 - Steel continuous casting method - Google Patents

Abstract

A continuous casting method of steel is provided that can reduce segregation and center porosity by causing a slab to undergo impact vibration under optimum conditions. In the continuous casting method of steel in which a slab having a rectangular cross section is cast while causing vibration in the slab with liquid core by disposing impact-vibration equipments on both short side surfaces of slab and continuously impacting those surfaces, the method includes the steps of: adjusting a vibration energy, a distance between shafts of adjacent guide rolls and a liquid core thickness, so that, among intersections generated by the impacting of the short side surface, between a curve of displacement ´(x) of the long side slab surface in a slab thickness-wise direction as defined by the following formulas (1) and (2) and a straight line ´(x) = 0.10 mm, a distance from an impact position of the intersection farther away from the coordinate origin is at least 200 mm; and impacting the short side, ´ x = exp - 1.5 × ln x / 200 × ”R / ”R 0 0.587 2 × ´max ´max = L 0 × E / E 0 0.5 × ”R / ”R 0 × t / t 0 0.446

Description

  The present invention relates to a steel continuous casting method in which a surface of a slab including an unsolidified portion is hit and cast while applying vibration to the slab.

  Internal defects, which are macro segregation called center segregation, V segregation, and reverse V segregation, are likely to occur at the center in the thickness direction of the slab cast by continuous casting and in the vicinity thereof. Center segregation is an internal defect in which solute components such as C, S, P, and Mn that are easily segregated (hereinafter also referred to as “segregation components”) appear in the final solidified portion of the slab. Segregation is an internal defect in which these segregation components are concentrated in a V shape or an inverted V shape in the vicinity of the final solidified portion of the slab.

  Products that have been hot-worked using slabs with macrosegregation are prone to toughness reduction and hydrogen-induced cracking, and when these products are processed into final products in the cold. , Cracking is likely to occur.

  The generation mechanism of segregation in the slab is considered as follows. That is, as solidification progresses, segregation components concentrate between the columns of columnar crystals that are solidified structures. The concentrated molten steel of the segregation component (hereinafter also referred to as “concentrated molten steel”) flows out from the columnar crystals due to shrinkage of the slab during solidification or swelling of the slab called bulging. The concentrated molten steel that has flowed out flows toward the solidification completion point of the final solidified portion, and solidifies as it is to form a concentrated band of segregation components. The concentration band of the segregation component thus formed is segregation.

  As measures for preventing segregation of slabs, it is effective to prevent the movement of the concentrated molten steel remaining between the columns of columnar crystals and to prevent local accumulation of these concentrated molten steel. Conventionally, various methods have been proposed.

  And in these patent documents, when casting the slab whose cross-sectional shape is a rectangle in the patent document 1, the present inventors use a striking vibration device disposed at least at one place on the short side surface side of the slab including the unsolidified portion. The continuous casting method of steel for casting while applying vibration to the slab by continuously striking the short side surface of the slab including the unsolidified portion having a central solid phase ratio of 0.1 to 0.9 Proposed.

  In addition, in the Patent Document 2, the present inventors in the casting direction when the position of the casting direction including the unsolidified portion of the slab having a rectangular cross-sectional shape is reduced by a plurality of guide roll pairs for reduction. In the range of the reduction region, a continuous casting method of steel was proposed in which at least one spot on the surface of the slab is continuously hit to cast the slab while applying vibration.

According to these methods, the columnar crystals in the middle of growth can be broken by the striking vibration of the slab, and the growth of the columnar crystals can be suppressed. Further, when the generated equiaxed crystal bridges, a space is formed, and segregation occurs in the space, but this space is destroyed by the impact. Therefore, equiaxed crystals can be packed at high density, and the concentrated molten steel can be finely dispersed between crystal grains, and the segregation such as center segregation, V segregation, and reverse V segregation is reduced, and the internal quality is good. A slab can be obtained.
Japanese Patent No. 3835185 (claims, paragraphs [0018] to [0020]) JP 2003-334461 A (claims, paragraphs [0013] to [0015])

  There is central porosity as an internal defect along with segregation. The center porosity is a small hole generated near the center in the thickness direction, which is the final solidification position, due to solidification shrinkage when the molten steel solidifies in continuous casting or heat shrinkage due to cooling after solidification. In order to improve the internal quality of the slab, it is required to reduce the center porosity as well as segregation. Further, it is required to investigate the detailed relationship between the vibration condition of the cast slab due to impact and the quality of the center part of the slab, to establish an appropriate vibration condition, and to improve the efficiency of continuous casting.

  The present invention has been made in view of the above-mentioned problems, and the problem is that the slab is struck and vibrated under appropriate conditions, so that a slab having good internal quality without segregation or central porosity is efficiently produced. An object of the present invention is to provide a continuous casting method of steel that can be obtained well.

  The present inventors examined a continuous casting method of steel for efficiently obtaining a slab having good internal quality without segregation or central porosity, and obtained the following findings (A) and (B).

(A) From the striking position of the slab short side surface in the region where the displacement in the thickness direction of the slab is 0.10 mm or more, which occurs when one short side surface of the slab having an unsolidified portion is struck. If the maximum distance is set to 200 mm or more in the direction perpendicular to the short side surface, segregation inside the slab can be reduced.

(B) The displacement in the thickness direction of the slab caused by striking varies depending on the interaxial distance of the guide roll, the striking energy, and the thickness of the unsolidified portion at the striking position of the slab.

  The present invention has been completed on the basis of the above knowledge, and the gist thereof is the following (1) and (2) steel continuous casting methods.

(1) When casting a slab having a rectangular cross section, at least a pair of striking vibration devices are arranged on both sides of the short side surface of the slab including the unsolidified portion, and the short side surface of the slab is continuously provided. The steel is continuously cast by applying vibration to the slab by striking the slab, wherein the casting defined by the following formulas (1) and (2) is performed by striking the short side surface. Two intersections of the displacement curve δ (x) in the slab thickness direction of the long side surface of the piece and the straight line δ (x) = 0.10 mm are generated, and the intersection of the intersections farther from the origin among the intersections Adjusting the vibration energy, the distance between the shafts of the guide roll and the unsolidified thickness so that the distance in the slab width direction from the strike position of the slab short side surface is 200 mm or more, and hitting the short side surface A method for continuous casting of steel.
δ (x) = exp [−1.5 × {ln (x / (200 × (ΔR / ΔR ₀ ) ^0.587 ))} ² ] × δ _max (1)
δ _max = L ₀ × (E / E ₀ ) ^0.5 × (ΔR / ΔR ₀ ) × (t / t ₀ ) ^0.446 (2)
Here, each symbol in the above formulas (1) and (2) means the following quantities.
x: Distance in the slab width direction (mm), where the strike position of the slab short side surface is 0,
δ (x): displacement in the slab thickness direction at the position x (mm),
δ _max : Maximum displacement (mm) in the slab thickness direction,
ΔR: the distance between the axes of the guide roll at the position of hitting the short side surface (mm),
E: Impact energy per side of one segment (J),
t: Unsolidified thickness (mm) of the slab at the striking position on the short side surface of the slab,
However, E ₀ = 39 (J), ΔR ₀ = 245 (mm), t ₀ = 26 (mm), and L ₀ = 0.114 (mm).

(2) The displacement δ (x) generated by striking on each of the left and right short side surfaces is made equal by making the phase of the time for periodically striking the opposing left and right short side surfaces of the slab to be equal to each other. The method of continuous casting of steel according to (1) above, wherein the overlapped displacement δ (x) is set to 0.10 mm or more over the entire width direction of the striking position.

  According to the method of the present invention, since the vibration of the long side surface of the slab caused by striking the short side surface of the slab can be applied over a wide range of the slab, the segregation or The central porosity can be reduced, and a slab excellent in internal quality can be obtained.

  The reason why the method of the present invention is defined as described above and preferred embodiments of the method of the present invention will be described below.

  The inventors conducted a continuous casting test while applying vibration to the slab by striking and analyzed the effect of vibration, and as described below, the influence of vibration on the internal quality of the slab. investigated.

<1. Relationship between slab internal quality and impact energy>
(1-1. Casting test conditions)
FIG. 1 is a diagram showing an arrangement of a continuous casting machine and a striking vibration device to which the continuous casting method of the present invention can be applied. FIG. 1 (a) shows a side view of the continuous casting machine, and FIG. These show the top view of the part which installed the impact vibration apparatus of the continuous casting machine. The continuous casting machine shown in the figure is a vertical bending die and includes a slab striking vibration device.

  The molten steel 4 injected into the mold 3 from the tundish (not shown) through the immersion nozzle 1 is cooled by spray water sprayed from the mold 3 and a group of secondary cooling spray nozzles (not shown) below it, A solidified shell 5 is formed to become a slab 7. The slab 7 is pulled out while being supported by the group of guide rolls 6 while holding the unsolidified portion therein. In the mold 3 of FIG. 1, a meniscus which is the molten metal surface 2 of the molten steel 4 is shown. The guide roll 6 is divided into a plurality of segments (not shown).

  Then, two pairs of striking vibration devices 8 are installed for each segment on the downstream side of the guide roll 6 group in the casting direction, and strike the short side surface of the slab 7. The striking vibration device 8 has a driving portion 10 and a striking die 9 attached to the tip portion thereof.

  In this continuous casting test, a mold 3 for a slab having a thickness of 300 mm was used. In order to investigate the influence of the impact vibration in the width direction, a wide slab of 2300 mm was used as the slab 7.

  In the casting test, steel types having the following composition used for thick steel plates were employed. That is, C: 0.05-1.00 mass%, Si: 0.04-0.60 mass%, Mn: 0.50-2.00 mass%, P: 0.020 mass% or less, S: 0 It is a steel type containing 0.006% by mass or less, with the balance being Fe and inevitable impurities.

  The casting speed was 0.58 to 0.61 m / min, and the amount of secondary cooling water was 0.62 to 0.73 L / kg-steel. The average temperature of the molten steel in the tundish was made almost constant in the range of the molten steel superheat degree ΔT = 30-50 ° C. ΔT is the difference between the actual molten steel temperature and the liquidus temperature of the molten steel.

  The two pairs of striking vibration devices 8 were arranged at a position of 22.5 m and 24.0 m on the downstream side in the casting direction from the meniscus 2 in the mold 3 with reference to the center of the mold 9 in the casting direction. The mold 9 of the striking vibration device 8 had a striking surface having a casting direction length of 1155 mm, a vertical direction height of 135 mm, and a mass of 500 kg. An air cylinder device was used for the drive unit 10 of the impact vibration device 8. The frequency of impact vibration on the short side surface of the slab 7 was 4 to 6 Hz, that is, the number of impacts per second was 4 to 6 times.

  By striking the short side surface of the slab, the columnar crystals in the middle of growth can be broken and the growth of the columnar crystals can be suppressed. Further, when the generated equiaxed crystal bridges, a space is formed, and segregation occurs in the space, but this space is destroyed by hitting. Therefore, equiaxed crystals can be filled with a high density, the concentrated molten steel can be finely dispersed between crystal grains, and segregation and central porosity can be reduced.

  The center solid phase ratio of the slab 7 is calculated by one-dimensional heat transfer calculation mainly using the casting speed and the amount of secondary cooling water as variables, and based on the result, a predetermined central solid ratio is obtained at the striking position. The conditions were sought. And the continuous casting on the said conditions was performed, hitting the short side surface of a slab.

(1-2. Evaluation of internal quality of slab)
The internal quality of the slab obtained by continuous casting performed while striking the short side surface of the slab was evaluated by evaluating the state of occurrence of central porosity.

(1-2-1. Evaluation method of occurrence of central porosity)
The occurrence of central porosity was evaluated by the following method. The sample for calculating the specific volume of the center porosity collected from the slab is 50 mm in length (in the thickness direction of the slab), 100 mm in width (in the width direction of the slab), and the thickness (in casting) in consideration of the specific gravity measurement accuracy. The casting direction of the piece was a 7 mm rectangular parallelepiped, and the surface processing accuracy was a finish according to JIS (triangle symbol ▽▽▽: maximum surface roughness 3.2 μm). The center of the thickness, based on the density at the position of 1/4 of the thickness in the thickness direction from the surface of the slab where the occurrence of the center porosity is considered to be little (hereinafter also referred to as “1/4 thickness position”) The occurrence of central porosity was evaluated based on the specific volume of central porosity calculated from the density of. The central porosity specific volume Vp was defined by the following equation (1) by the average density ρ ₀ at the ¼ thickness position and the average density ρ at the center in the thickness direction.
Vp≡1 / ρ−1 / ρ ₀ (1)

FIG. 2 is a cross-sectional view of a slab showing a sampling position of a sample for calculating the center porosity ratio volume. In FIG. 2, the area | region of the one end side of the width direction of the cross section perpendicular | vertical to the casting direction of a slab is shown. The average density ρ ₀ at the ¼ thickness position of the slab was calculated by taking a total of two samples 7a, one each from both ends in the width direction of the slab, and averaging the respective densities. The average density ρ at the center in the thickness direction was calculated by taking a total of six samples 7b, 7c, and 7d from three ends in the width direction of the slab and averaging the respective densities. The positions at which the samples 7a to 7d were taken are based on the center of the sample, the samples 7a and 7b are 190 mm from the slab short side surface, the sample 7b is 320 mm from the slab short side surface, and the sample 7d is from the slab short side surface. 425 mm.

Then, based on the center porosity ratio volume Vp _{0 of} the slab that was not struck and the center porosity ratio volume Vp ₁ of the slab that was struck, the center porosity ratio volume reduction amount −ΔVp was defined by the following equation (2). .
-ΔVp≡Vp ₀ -Vp ₁ (2)

(1-2-2. Evaluation results of central porosity occurrence)
FIG. 3 is a graph showing the relationship between the impact energy per side of one segment and the amount of decrease in the central porosity ratio volume. In the graph, the reduction amount -ΔVp of the center porosity ratio volume is calculated and arranged for each slab that was struck with different impact energies. From the relationship shown in the graph, it was confirmed that when the impact energy E per side of one segment exceeds 25 J, the center porosity ratio volume decreases at the end in the slab width direction. When the regression equation is calculated with respect to the relationship between the impact energy E per one side of the segment and the amount of decrease in the central porosity ratio volume −ΔVp in the graph, the following equation (3) is obtained.
-ΔVp [cm ³ / g] = 0.0049347 × E [J]-1.297487 (3)

And from FIG. 3, when the impact energy E = 39J, the knowledge that the reduction effect of the central porosity is about −ΔVp = 0.57 × 10 ⁻⁴ cm ³ / g can be obtained. It was. Further, as a result of macro observation, it was found that the cast slab subjected to impact tended to have less granular segregation than the slab not subjected to impact.

<2. Generalization of the relationship between slab internal quality and impact energy>
On the basis of the above findings, the present inventors further examined generalization of the above results relating to the slab short side impact.

  FIG. 4 is a schematic diagram of a vibration model by striking a slab having an unsolidified portion. In the figure, the solidified shell 5 of the slab 7 is in a state of being restrained by a guide roll 6. In this state, the short side surface of the slab 7 is hit by the hit vibration device 8.

  The shape of the die 9 of the impact vibration device 8 was a rectangular parallelepiped having a length a in the casting direction of 1200 to 1600 mm, a thickness b of 140 mm, and a width c in the slab thickness direction of 200 mm. The slab 7 had a width of 2300 mm and a thickness of 300 mm. Using such a three-dimensional model, numerical analysis was performed on the displacement of the surface (long side surface) due to vibration of the slab 7.

From the numerical analysis result of the surface displacement due to the impact vibration in the slab 7, the present inventors have found that the maximum displacement δ _max in the slab thickness direction is a direction perpendicular to the short side surface from the impact position of the short side surface (the slab It was found that the value δ _{x = 200} mm at a position of 200 mm in the width direction) was almost equal.

In addition, the present inventors have examined the relationship between the displacement fluctuation width L at the solid-liquid interface position and various factors affecting the displacement fluctuation width L in the vibration region. It was found that energy E is arranged and the relationship can be described by the following equation (a). Hereinafter, each symbol with subscript 0 indicates a representative condition.
L / L ₀ = (E / E ₀ ) ^0.5 (a)

Furthermore, the influence on the displacement fluctuation range by the axial distance ΔR of the guide roll at the position where the short side surface is struck and the unsolidified thickness t of the slab at the position where the short side surface is struck can be arranged independently. It has been found that the displacement fluctuation width in the long side plate thickness direction at a position of 200 mm in the direction perpendicular to the short side surface from the strike position on the short side surface changes substantially in direct proportion to ΔR. Based on these findings, the following formula (b) was obtained by extending the formula (a) as an estimation formula for the displacement fluctuation width L.
L / L ₀ = (E / E ₀ ) ^0.5 × (ΔR / ΔR ₀ ) × f (t, t ₀ ) (b)
Here, f (t, t ₀ ) represents an influence term of the unsolidified thickness of the slab. Assuming that f (t, t ₀ ) is proportional to the power of the dimensionless quantity t / t ₀ , the following equation (c) is obtained as an example of f from the experimental simulation results.
f (t, t ₀ ) = (t / t ₀ ) ^0.446 (c)

Then, the expression (c) was substituted into the expression (b), and finally the following expression (4) was obtained as an estimation expression of the displacement fluctuation width L (= δ _max ).
δ _max ≈δ _{x = 200 mm} = L ₀ × (E / E ₀ ) ^0.5 × (ΔR / ΔR ₀ ) × (t / t ₀ ) ^0.446 (4)
Here, each symbol in the above formula (4) means the following various quantities.
E: Impact energy per side of one segment (J),
ΔR: the distance between the axes of the guide roll at the position of hitting the short side surface (mm),
t: Unsolidified thickness (mm) of the slab at the striking position on the short side surface of the slab.
E ₀ , ΔR _0, and t ₀ are numerical values under the condition that the central porosity reduction effect of E, ΔR, and t is the greatest, and L ₀ is the maximum in the slab thickness direction when the central porosity reduction effect is the largest. These are representative conditions for displacement, and are the following constant group (5). Hereinafter, this condition is also referred to as condition (5).
E ₀ = 39 (J), ΔR ₀ = 245 (mm), t ₀ = 26 (mm), L ₀ = 0.114 (mm) (5)

The inventors calculated the displacement in the slab thickness direction of the slab surface (long side surface) at the position of the distance x in the direction perpendicular to the short side surface from the striking position of the slab short side surface, calculated by numerical analysis. It has been found that when δ (x) is approximated by a lognormal distribution, it can be generalized as in the following equation (6) using δ _max in the above equation (4).
δ (x) = exp [−1.5 × {ln (x / (200 × (ΔR / ΔR ₀ ) ^0.587 ))} ² ] × δ _max (6)

FIG. 5 is a graph showing the relationship between the distance from the short side impact position and the displacement in the slab thickness direction. The horizontal axis of the graph is the distance x in the direction perpendicular to the short side surface from the striking position of the short side surface of the slab, and the vertical axis is the dimensionless displacement (δ (x) in the slab thickness direction of the slab surface. (Dimensionless value with the maximum displacement taken as 1 divided by δ _max ). In the graph, ◯ indicates a value calculated by numerical analysis, and ● indicates a value approximated by a lognormal distribution. From the results shown in the graph, it can be seen that the values calculated by numerical analysis are approximated with a lognormal distribution with high accuracy.

<3. Relationship between slab internal quality and slab displacement due to impact>
FIG. 6 is a graph showing the relationship between the maximum displacement δ _max in the slab thickness direction and the reduction amount −ΔVp of the center porosity ratio volume. The relationship shown in the graph is as follows: δ _max and − from the equation (3) and the equation (4) in which ΔR = 245 (mm) and t = 26 (mm) are applied by applying the condition (5). The relationship with ΔVp was obtained and created. As for the unsolidified thickness t of the slab at the striking position on the short side of the slab, the unsolidified thickness at the entrance of the segment where the striking vibration device 8 is arranged by heat transfer solidification calculation at a casting speed of 0.7 m / min. The thickness was calculated and used.

The present inventors have found from the results shown in FIG. 6 that, in the case of a slab having a thickness of 300 mm and a width of 2300 mm, the center porosity ratio volume decreases if δ _max is 0.10 mm or more.

Further, the present inventors have further investigated the relationship between the slab internal quality and the displacement of the slab due to impact, and the distance x from the short side surface where δ _max is 0.10 mm or more and δ _max is If the displacement x at a position where the distance x is less than 200 mm and the distance x is 200 mm or more is 0.10 mm or more at a position where δ _max is 200 mm or more, segregation or center over a wide range inside the slab It has been found that the porosity can be reduced and the internal quality of the slab can be improved. In addition, this continuous casting test was carried out with two pairs of impact vibration devices installed, but even if the impact vibration devices are one pair or three pairs or more, the effect of improving the internal quality of the slab is the same as in the case of two pairs. It was confirmed that

<4. Relationship between impact energy and vibration reach distance by impact>
When the above equation (6) is solved for x, the following equation (7) is obtained as a function of the displacement δ in the slab thickness direction and the inter-axis distance ΔR of the guide roll at the position where the short side surface is hit.
x = 200 × (ΔR / ΔR ₀ ) ^0.587 × exp [{− ln (δ / δ _max ) /1.5} ^0.5 ] (7)

FIG. 7 is a graph showing the relationship between the impact energy per side of one segment and the vibration reach distance. The maximum value x ^* of the distance x in the direction perpendicular to the short side surface from the striking position of the short side surface of the slab in the region where the displacement δ in the slab thickness direction by impact is 0.10 mm or more is defined as the vibration reach distance. To do. The ● marks in the graph are the results when the condition (5) is applied, the thickness of the slab is 300 mm, and the impact energy E per side of one segment on the short side of the slab is 40 J. , X ^* = 200 mm. The curve in FIG. 7 was calculated from the above equation (7) and the conditions indicated by ●. From the relationship shown in the graph, it is understood that the vibration reach distance x ^* can be increased by increasing the impact energy E. For example, by increasing the impact energy E from 40J to 65J, the vibration reach distance x ^* is increased by 25% from 200 mm to 250 mm. That is, by increasing the impact energy E, it is possible to improve the quality of the central portion in the slab thickness direction in the vicinity of the end portion in the slab width direction where central porosity is likely to occur due to solidification delay.

<5. Relationship between guide roll axis distance and striking vibration reach distance>
FIG. 8 is a graph showing the relationship between the impact energy per one segment side and the vibration reach distance when the distance between the axes of the guide rolls is changed. FIG. 8 is a graph for a case where the guide roll is hit under the same conditions as in FIG. 7 except that the inter-axis distance ΔR is 245 mm or 400 mm. From the relationship shown in the graph, it can be seen that the vibration reach distance x ^* increases when the inter-axis distance ΔR of the guide roll is increased from 245 mm to 400 mm. That is, when the slab is a slab having a large ratio of the long side length to the short side length, the slab width is wide and bulging between the guide rolls is likely to occur. I can't take it big. On the other hand, when the slab is a bloom with a small ratio of the long side length to the short side length, the slab width is narrow and the bulging between the guide rolls is small. Therefore, it is advantageous in that the impact effect can be obtained in a wide range.

<6. About the effect of batting from both sides>
FIG. 9 is a graph showing the influence of impact from the short side surfaces at both ends in the width direction of the slab. In the graph, the horizontal axis is the distance y in the direction perpendicular to the short side surface from the center in the width direction of the slab, and the vertical axis is the displacement δ in the slab thickness direction. The slab hit is a bloom having a width of about 400 mm, the guide roll axial distance ΔR is 400 mm, the impact energy E per segment piece side is 45 J, and only the short side on the left side of the slab in the casting direction or the right short side The calculation result about the case where only a side surface is struck and the case where a short side surface on both sides is struck simultaneously is shown. From the results shown in the graph, the slab thickness direction displacement δ _L when only the short side surface on the left side in the casting direction of the slab is struck and the slab thickness direction when only the right side surface is struck It can be seen that the displacement δ _D in the slab thickness direction when the short side surfaces on both sides of the slab are hit simultaneously is superimposed when the displacement δ _R is superimposed.

  When only the short side surface on the left side in the casting direction of the slab or only the short side surface on the right side is struck, the displacement of the slab thickness direction in the region where the displacement δ is 0.10 mm or more, The distance in the direction perpendicular to the short side surface from the striking position is about 300 mm, and the displacement δ cannot be 0.10 mm or more over the entire width. However, by simultaneously hitting the short side surfaces on both sides, the displacement δ can be made 0.10 mm or more over the entire width of the hitting position. In addition, as can be seen from FIG. 9, when the short side surfaces on both sides are hit simultaneously, the maximum value of the displacement δ reaches 0.40 mm at the center in the width direction of the slab, and the displacement δ can be greatly increased. It is possible to further improve the internal quality of the slab.

  According to the method of the present invention, since the vibration of the long side surface of the slab caused by striking the short side surface of the slab can be applied over a wide range of the slab, the segregation or The central porosity can be reduced, and a slab excellent in internal quality can be obtained. Therefore, the method of the present invention can be widely applied as a continuous casting method of a slab having good internal quality.

It is a figure which shows arrangement | positioning of the continuous casting machine and impact vibration apparatus which can apply the continuous casting method of this invention, (a) shows the side view of a continuous casting machine, (b) is the impact vibration of a continuous casting machine The top view of the part which installed the apparatus is shown. It is a cross-sectional view of the slab which shows the collection position of the sample for center porosity ratio volume calculation. It is a graph which shows the relationship between the impact energy per one segment side and the amount of reduction | decrease of a center porosity specific volume. It is a schematic diagram of the vibration model by the impact of the slab which has an unsolidified part. It is a graph which shows the relationship between the distance from a short side surface impact position, and the displacement of a slab thickness direction. It is a graph which shows the relationship between the maximum displacement (delta) _max of slab thickness direction, and the reduction | decrease amount-(DELTA) Vp of a center porosity ratio volume. It is a graph which shows the relationship between the impact energy per one segment side, and a vibration reach distance. It is a graph which shows the relationship between the impact energy per one segment side, and the vibration reach distance, and shows the influence of the interaxial distance of a guide roll. It is a graph which shows the influence of the impact from each short side surface of the width direction both ends of a slab.

Explanation of symbols

1: immersion nozzle, 2: molten steel surface (meniscus), 3: mold, 4: molten steel,
5: Solidified shell 6: Guide roll 7: Cast slab
7a, 7b, 7c, 7d: slab sample, 8: impact vibration device, 9: mold,
10: Drive unit

Claims (2)

When casting a slab having a rectangular cross section, at least a pair of striking vibration devices are arranged on both sides of the short side surface of the slab including the unsolidified portion, and the short side surface of the slab is continuously struck. By this, it is a continuous casting method of steel that casts while applying vibration to the slab,
Due to the impact on the short side surface, the displacement curve δ (x) and straight line δ (x) = 0 in the slab thickness direction of the long side surface of the slab defined by the following formulas (1) and (2) Vibration energy such that two intersections with 10 mm occur, and the distance in the slab width direction from the striking position of the short side surface of the slab at the intersection far from the origin of the intersections is 200 mm or more, A continuous casting method for steel, characterized by striking a short side face by adjusting an interaxial distance and an unsolidified thickness of a guide roll.
δ (x) = exp [−1.5 × {ln (x / (200 × (ΔR / ΔR ₀ ) ^0.587 ))} ² ] × δ _max (1)
δ _max = L ₀ × (E / E ₀ ) ^0.5 × (ΔR / ΔR ₀ ) × (t / t ₀ ) ^0.446 (2)
Here, each symbol in the above formulas (1) and (2) means the following quantities.
x: Distance in the slab width direction (mm), where the strike position of the slab short side surface is 0,
δ (x): displacement in the slab thickness direction at the position x (mm),
δ _max : Maximum displacement (mm) in the slab thickness direction,
ΔR: the distance between the axes of the guide roll at the position of hitting the short side surface (mm),
E: Impact energy per side of one segment (J),
t: Unsolidified thickness (mm) of the slab at the striking position on the short side surface of the slab,
However, E ₀ = 39 (J), ΔR ₀ = 245 (mm), t ₀ = 26 (mm), and L ₀ = 0.114 (mm).   By making the phase of time for periodically hitting the left and right short side faces of the slab opposite to each other, the displacement δ (x) generated by hitting on each of the left and right short side faces is superimposed on each other, 2. The steel continuous casting method according to claim 1, wherein the superposed displacement δ (x) is 0.10 mm or more over the entire width direction of the striking position.

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