JP5029694B2 - Stroke vibration device for continuous casting - Google Patents

Description

  The present invention relates to a striking vibration device that applies vibration due to striking to the short side surface of a slab during continuous casting in order to improve center segregation and the like.

Macro segregation called center segregation or V segregation is likely to occur at the center portion in the thickness direction and in the vicinity of the continuously cast slab. Hereinafter, this macro segregation is also referred to as an internal defect.
Among these, the center segregation is an internal defect that appears in the final solidified portion of the slab by concentrating solute components (hereinafter also referred to as segregation components) such as C, S, P, and Mn. V segregation is an internal defect in which these segregation components are concentrated in a V shape in the longitudinal section of the slab in the vicinity of the final solidified portion of the slab.

  When these slabs in which macro segregation has occurred are hot processed into products, toughness reduction, hydrogen-induced cracking, and the like are likely to occur. Further, when these products are processed into a final product in a cold state, cracks are likely to occur.

By the way, the generation mechanism of segregation in a slab is considered as follows.
That is, as the solidification progresses, segregation components are concentrated between the columnar crystal trees which are solidified structures. The molten steel enriched in the segregation component flows out between the columns of columnar crystals due to shrinkage of the slab during solidification or blistering 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 become a concentrated zone of segregation components. The concentrated band of the segregation component thus formed is segregation.

  In order to prevent such segregation of the slab, it is necessary to prevent the movement of the molten steel enriched in the segregation component remaining between the columns of the columnar crystals, and to prevent these concentrated molten steel from locally accumulating. It is effective to do.

Therefore, during continuous casting, an air hammer is installed between the rolls arranged on the long side of the slab, and impact vibration with an amplitude of about 2.0 mm or less per minute is applied to the slab moving between the rolls. Patent Document 1 proposes a method of giving 10 to 100 times.
Japanese Unexamined Patent Publication No. 51-128631

In addition, the applicant, when rolling down the position including the unsolidified portion of the slab having a rectangular cross section with a plurality of guide roll pairs for reduction, while casting while giving vibration to the slab, This is proposed in Patent Document 2. In this method, at least one spot on the surface of the slab is continuously hit within the range of the reduction region.
Japanese Laid-Open Patent Publication No. 2003-334641

  The method described in Patent Document 2 bulges a slab at a position including an unsolidified portion, and at least one pair of the bulged slab until solidification of the central portion in the thickness direction is completed. This is a method of reducing with a pair of reduction rolls. At that time, a method for casting while applying vibration to the slab has been proposed. That is, it is a method of continuously hitting at least one location on the slab surface within the range of the casting direction region from the start of bulging to the start of reduction or within the range of the reduction region in the casting direction.

However, the method proposed in Patent Document 1 has the following major problems in order to fully exhibit the effect of reducing center segregation.
Between the rolls arranged on the long side of the slab, the slab is easily bulged. When impact vibration is applied to the long side of the bulged slab, a large amplitude cannot be applied to the central portion in the thickness direction of the slab. Moreover, since it is necessary to install an air hammer between rolls, there exists a possibility that the spray arrangement for secondary cooling of a slab between rolls may be inhibited. Therefore, continuous vibrations cannot be applied when appropriate secondary cooling is performed. Furthermore, it is difficult to propagate sufficient vibration energy to the slab with 10 to 100 impact vibrations per minute.

  On the other hand, the method of Patent Document 2 is effective in preventing segregation of a slab. However, as a result of subsequent studies by the inventors, it has been found that the segregation may not be sufficiently reduced depending on the shape of the slab.

  The reason is that when the slab is struck from the short side, when the slab width is large, the impact vibration does not sufficiently propagate to the inside of the slab near the center in the width direction. In this case, since the columnar crystal in the middle of growth is not broken, the columnar crystal grows and a fine crystal structure cannot be generated. Furthermore, vibration is not sufficiently transmitted to the equiaxed crystal formed in the vicinity of the final solidified portion at the center in the width direction, and the equiaxed crystal is likely to bridge.

  Incidentally, the test conditions described in paragraphs 0039 to 0041 of Patent Document 2 (vibration amplitude is ± 3.0 mm, vibration frequency is 120 times / minute (2 Hz), mold dimensions are 200 mm × 100 mm × 400 mm (weight calculation value is In 62.4 kg)), the vibration energy is 7.8 J when the impact speed is 0.5 m / sec.

  The problem to be solved by the present invention is that in conventional hitting performed from the short side of the slab during continuous casting, the occurrence of segregation such as center segregation and V segregation is effectively prevented as the slab width increases. The point is that there are cases where it is not possible.

The striking vibration device during continuous casting of the present invention is
In order to effectively prevent the occurrence of segregation of the slab by effectively hitting the slab including the unsolidified portion from the short side surface side even in the slab having a large slab width,
When continuously casting a slab having a rectangular cross section, the slab has a central solid phase ratio f _S at the center of the slab thickness of at least 0.1 to 0.9 per 1 m in the casting direction length. Of the slab at least at one location where the central solid fraction f _S is in the range of 0.1 to 0.9. A device that strikes the short side surfaces on both sides continuously in the slab width direction with a striking vibration frequency of 4 to 12 Hz and a vibration energy of 30 to 150 J,
A mold that strikes the short side of the slab,
A striking device that generates periodic vibrations and transmits the vibrations to the mold;
An impact positioning device for setting a distance between the mold and the short side surface of the slab;
The mold has a structure capable of hitting the short side surface of the slab at least between two pairs of adjacent pinch rolls of a light rolling zone composed of a plurality of pinch roll pairs as a whole,
The hitting positioning device sets the distance between the tip end surface of the mold and the slab short side surface at the pull back position of the mold after detecting the pressing position of the mold to the slab short side surface, or The most important feature is that the impact positioning is performed in a state in which a guide for setting the interval between the slab and the tip surface of the mold is pressed.

The central solid phase ratio f _S is calculated from the liquidus temperature T _L , the solidus temperature T _S, and the temperature T at the thickness center of the molten steel, f _S = (T _L −T) / (T _L − T _S ). When the temperature T at the thickness center of the slab is equal to or higher than the liquidus temperature _{TL of the} molten steel, f _S = 0, and when the temperature T at the thickness center is lower than the solidus temperature T _{S of the} molten steel, f _S = 1.0. The temperature T at the center of the slab thickness can be obtained by one-dimensional unsteady heat transfer analysis calculation in the slab thickness direction in consideration of the casting speed, surface cooling of the slab, physical properties of the cast steel type, and the like.

  According to the present invention, even in the case of a slab having a large slab width, occurrence of segregation such as center segregation and V segregation is effectively prevented, and a slab having good internal quality can be obtained.

It is a schematic diagram which shows the example of the pinch roll pair which attached the striking device from the short side surface direction of slab. It is the figure explaining the positional relationship of the metal mold | die of a striking device, and a slab, (a) is a figure which shows the standby position of a striking device, (b) shows the state which pressed the metal mold | die on the short side surface of the slab. (C) is a diagram showing a state in which the mold is returned by a predetermined amount starting from the position (b). It is the figure explaining the positional relationship of the metal mold | die of another striking device, and a slab, (a) is a figure which shows the standby position of a striking device, (b) makes a pressing guide contact | abut to the short side surface of a slab. FIG. 5C is a diagram showing a state during hitting. It is the figure which showed the casting direction length and the unsolidified thickness of the area | region where the center solid phase rate in the case of high carbon steel is 0.1-0.9. It is the figure which showed the casting direction length and the unsolidified thickness of the area | region where the center solid phase rate in the case of medium carbon steel is 0.1-0.9. It is the figure which showed the experimental result.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cast slab 2a, 2b Pinch roll 3 Mold 3a Striking plate 6 Striking device 7 Striking positioning device 8 Pressing guide

  When striking from the short side of the slab during continuous casting, if the slab width is large, the occurrence of segregation such as center segregation or V segregation may not be effectively prevented. The present invention achieves this problem by enabling the die structure to be continuously and collectively hit with at least the entire short side surface of the slab located between two adjacent pairs of pinch rolls. did.

  Hereinafter, the best mode for carrying out the present invention will be described in detail together with the process up to the establishment of the invention.

  As described above, when the slab is struck from the short side surface side, when the slab width is large, vibration due to the impact is not sufficiently propagated to the inside of the vicinity of the central portion in the width direction of the slab. In this case, since the columnar crystals in the middle of growth cannot be broken, the columnar crystals cannot grow into a fine crystal structure, and a sufficient segregation reduction effect cannot be obtained. Furthermore, vibration is not sufficiently transmitted to the equiaxed crystal formed in the vicinity of the final solidified portion at the center in the width direction of the slab, and the equiaxed crystal is easily bridging, and a sufficient segregation reducing effect cannot be obtained.

  In view of this, the inventors repeated experiments in which impact was imparted from the surfaces of the short sides facing both sides of the slab including the unsolidified portion in order to prevent the occurrence of center segregation and V segregation. By this experiment, it was investigated how the slab was struck from the side of the short side to sufficiently propagate the impact vibration to the inside of the slab near the center in the width direction.

As a result, the inventors have found that there is a vibration frequency and vibration energy at which a striking vibration effect is obtained when the center solid phase ratio f _S of the slab is in the range of 0.1 to 0.9. Furthermore, it has also been found that hitting almost the entire range is extremely effective in reducing segregation.

And when the inventors cast a slab having a rectangular cross section, the central solid phase ratio f _S at the central portion in the thickness direction of the slab is lightly reduced within a range of at least 0.1 to 0.9. A continuous casting method for steel was proposed (Japanese Patent Application No. 2006-53057). In this method, when the light reduction is performed, the central solid phase ratio f _S is continuously hit in the width direction of the slab at at least one position within the above range.

  At that time, light reduction is continuously performed so that the rolling reduction in the thickness direction of the slab is within 1% per 1 m in the casting direction length. Further, the opposing short side surfaces of the slab are continuously struck in the slab width direction with a striking vibration frequency of 4 to 12 Hz and a vibration energy of 30 to 150 J.

  In Japanese Patent Application No. 2006-53057, an apparatus for carrying out the continuous casting method is proposed. This device is a striking vibration device having a structure in which the entire short side surfaces of the short side surfaces on both sides of the slab in at least one segment of the segments composed of a plurality of guide rolls can be hit collectively. .

By the way, the light reduction in continuous casting of steel is not performed by the segment comprised by a some guide roll from the characteristic of the structure of a continuous casting machine, and may be performed by a pinch roll part.
When the inventor conducted a hitting test in the continuous casting method of steel proposed in Japanese Patent Application No. 2006-53057 in the pinch roll part, the same effect as when hitting in the segment was obtained. Was made.

  When hitting in such a pinch roll part, as shown in Table 1 below, the structure is simpler, the installation space can be easily secured, and the maintenance of the equipment is easier than hitting in the segment. There is an advantage that can be done.

The impact vibration device at the time of continuous casting of the present invention was made based on the above knowledge,
When continuously casting a slab having a rectangular cross section, the slab has a central solid phase ratio f _S at the center of the slab thickness of at least 0.1 to 0.9 per 1 m in the casting direction length. Of the slab at least at one location where the central solid fraction f _S is in the range of 0.1 to 0.9. A device that strikes the short side surfaces on both sides continuously in the slab width direction with a striking vibration frequency of 4 to 12 Hz and a vibration energy of 30 to 150 J,
A mold that strikes the short side of the slab,
A striking device that generates periodic vibrations and transmits the vibrations to the mold;
An impact positioning device for setting a distance between the mold and the short side surface of the slab;
The mold has a structure capable of hitting the short side surface of the slab at least between two pairs of adjacent pinch rolls of a light rolling zone composed of a plurality of pinch roll pairs as a whole,
The hitting positioning device sets the distance between the tip end surface of the mold and the slab short side surface at the pull back position of the mold after detecting the pressing position of the mold to the slab short side surface, or The hitting positioning is performed in a state where a guide for setting the interval between the cast piece and the tip surface of the mold is pressed.

  The striking vibration device at the time of continuous casting according to the present invention is shown in FIG. 1 between a pair of pinch rolls 2a and 2b arranged on the downstream side in the casting direction of a slab 1 solidified and cast in a mold. A mold 3 or the like is arranged.

  In FIG. 1, reference numeral 3 denotes a mold for hitting the short side surface of the slab 1. This mold 3 has a structure having a striking plate 3a between at least two adjacent pairs of pinch rolls 2a, 2b among a plurality of pairs of pinch rolls 2a, 2b. With this structure, the entire short side surface of the slab 1 positioned between at least two adjacent pairs of pinch rolls 2a and 2b can be integrally and continuously hit. The mold 3 is preferably made of a casting from the viewpoints of durability and heat resistance.

  By the way, bridging such as equiaxed crystal occurs at a position where the central solid fraction of the slab 1 is 0.1 or more. However, bridging may occur again if bridging is not completely prevented by hitting. Accordingly, it is desirable that the center solid phase ratio of the slab 1 is sufficiently continuously hit within a range of 0.4 or more, and it is preferable to hit the entire length between a plurality of pairs of pinch rolls 2a and 2b.

  Further, as will be described later, the center solid phase ratio of the slab is 0.1 to 0.9, and the position constantly changes during actual operation. Therefore, there may be cases where it is sufficient to strike between two adjacent pairs of pinch rolls 2a and 2b, and there are cases where it is necessary to strike between pairs of adjacent three stages of pinch rolls 2a and 2b as shown in FIG. However, hitting a long range in order to apply to all the ranges of the central solid fraction results in excessive equipment costs. Therefore, as a range in which a vibration effect can be obtained, for example, a pair of adjacent three-stage pinch rolls 2a and 2b Strike between them.

  That is, it is important that the slab 1 vibrates over a wide range in the casting direction, and if possible, the length of the mold 3 in the casting direction is such that the entire area of the plurality of pairs of pinch rolls 2a and 2b can be hit. It is desirable to do. However, in reality, the pair of pinch rolls 2a and 2b may be placed in or taken out from the continuous casting machine, so that the length that can be struck is made as long as possible so long as various continuous casting apparatuses do not interfere with each other. Is desirable.

  The pair of pinch rolls 2a and 2b is generally structured such that the amount of reduction can be adjusted by a hydraulic cylinder 5 or the like attached to the upper frame 4 and light reduction can be avoided.

  Reference numeral 6 denotes a striking device having the die 3 attached to the tip thereof, which generates periodic vibrations and transmits the vibrations to the die 3. For example, an air cylinder is employed. This striking device 6 is disposed, for example, at two locations on the short side surface side on both sides of the slab 1 including the unsolidified portion.

  7 is an impact positioning device, and the mold 3 is pressed against the short side surface of the slab 1 from the standby position shown in FIG. 2A (see FIG. 2B). This hitting positioning device detects the pressing position, and then, at the retracted position of the mold 3 (see FIG. 2C), the distance L (the hitting amplitude) between the tip surface of the mold 3 and the short side surface of the slab 1 : Approx. 8 mm).

  The hit positioning device 7 is not limited to the configuration shown in FIG. 2, and may have the configuration shown in FIG. 3. The hitting positioning device 7 of FIG. 3 makes the pressing guide 8 abut against the short side surface of the slab 1 from the standby position shown in FIG. And a distance L (striking amplitude: about 8 mm) between the slab 1 and the short side surface of the slab 1. This striking positioning device 7 keeps the pressing guide 8 pressed against the short side surface of the slab 1 during the striking shown in FIG. In addition, the arrangement conditions of the pressing guide 8 are set in advance so that the interval L between the mold 3 and the slab 1 becomes a predetermined interval.

  Since the distance L between the mold 3 and the short side surface of the slab 1 varies depending on the width of the slab 1 to be cast, the distance L between the mold 3 and the slab 1 can be actually set on the basis of the short side surface of the slab 1 being cast. is necessary. This interval L affects the stroke of the striking device 6. When the stroke is insufficient, the striking speed at the time of striking cannot be secured, and sufficient vibration energy cannot be obtained. Therefore, at the start of striking, the relative position adjustment between the mold 3 and the short side surface of the slab 1 is performed as positioning.

When continuously casting the slab 1 having a rectangular cross section using the apparatus of the present invention, the central solid phase ratio f _S at the center of the slab thickness is in the range of at least 0.1 to 0.9, Light rolling is continuously performed so that the rolling reduction in the thickness direction of the slab 1 is within 1% per 1 m in the casting direction length. At the same time, in at least one place where the central solid fraction f _S is in the range of 0.1 to 0.9, the short side surfaces on both sides of the slab 1 facing each other have an impact vibration frequency of 4 to 12 Hz and vibration energy. Hits continuously in the slab width direction at 30 to 150 J.

In the present invention, the short side surfaces of the opposite sides of the slab 1 are continuously hit at at least one location within the range where the central solid phase ratio f _S of the slab thickness center is 0.1 to 0.9. The reason is as follows.

  Since bridging such as equiaxed crystals occurs at a position where the central solid fraction is 0.1 or more, the formation of equiaxed crystals is sufficient at the position of the slab 1 where the central solid fraction is less than 0.1. This is because the effect of hitting the slab 1 is small. Further, if the central solid phase ratio exceeds 0.9, the unsolidified molten steel becomes difficult to vibrate and flow, so that the space formed by bridging or bridging such as equiaxed crystal is caused by striking the slab 1. This is because it becomes difficult to destroy.

  FIG. 4 shows a case where a high carbon steel (C = 0.40 mass%) having a thickness of 300 mm is continuously cast at a casting speed of 0.75 m / min and a secondary cooling specific water amount of 0.8 liter / kg. FIG. 6 is a diagram showing a casting direction length and an unsolidified thickness in a region where a central solid phase ratio of a slab is 0.1 to 0.9.

  In the present invention, the central solid phase ratio in the range of 0.1 to 0.9 is a long region in the casting direction as shown in FIG. Note that two double arrows in FIG. 4 show an example in which a striking plate for applying vibration to the slab is arranged at a distance of these two locations from the mold exit side.

Accordingly, in the example of the striking plate of FIG. 4, the short side surfaces on both sides of the slab are continuously struck in the slab width direction in the range where the central solid phase ratio f _S is 0.4 to 0.8. This is an example.

FIG. 5 shows a case where a medium carbon steel (C = 0.06 mass%) having a thickness of 250 mm is continuously cast at a casting speed of 1.0 m / min and a secondary cooling specific water amount of 0.8 liter / kg. FIG. 6 is a diagram showing the casting direction length and the unsolidified thickness in the region where the center solid phase ratio f _S of the slab is 0.1 to 0.9.

In addition, two double arrows in FIG. 5 indicate an example in which a striking plate for applying vibration to the slab is disposed at a distance of these two locations from the mold exit side.
The example of the striking plate of FIG. 5 casts the short side surfaces on both sides of the slab 1 facing each other at 0.25 to 1.0 including the central solid phase ratio f _S in the range of 0.25 to 0.9. This is an example of striking continuously in the single width direction.

  In the case of the present invention, the reduction ratio in the thickness direction of the slab 1 is within 1% per 1 m of the casting direction length in the range where the central solid fraction fs at the thickness center of the slab is at least 0.1 to 0.9. Thus, the slab is continuously lightly reduced. The reason for this is that when the inventors calculated the roll interval (squeezing amount) of the pair of pinch rolls 2a and 2b in consideration of the solidification shrinkage amount and the heat shrinkage amount, the range having the effect of reducing the center segregation is the length in the casting direction. This is because the rolling reduction in the thickness direction of the slab 1 is within 1% per meter.

  In other words, when the rolling reduction in the thickness direction of the slab 1 greatly exceeds 1% per 1 m in the casting direction length in the range of low solid fraction, the strain at the solidification interface increases and internal cracks occur. Cheap. In the case of continuous light reduction, it is sufficient to reduce the internal cracking while reducing the amount more than the amount of solidification shrinkage. In this case, the reduction ratio is the thickness direction of the slab 1 per 1 m of the casting direction length. Within 1%.

  Moreover, in this invention, not the long side surface of a slab but a short side surface is hit | damaged continuously. Between the rolls on the long side, the slab is easy to bulge, and when striking vibration is applied to the long side surface that is bulged, fluctuation of the molten metal surface on the upstream side is promoted. Moreover, since the slab is bulging, a large amplitude cannot be given to the thickness center part of the slab. Moreover, since the impact imparting means is installed between the rolls, there is a possibility that the spray arrangement for secondary cooling of the slab between the rolls may be hindered, so that continuous vibration cannot be imparted.

  On the other hand, when applying impact vibration to the short side surface, even if it receives displacement due to vibration, a large volume change does not occur compared to the long side, so when applying impact vibration to the long side surface Such a problem does not occur. Moreover, there are few facilities problems for installing a hit | damage provision means.

  For example, when the slab width is 2300 mm and the mold 3 is 200 mm wide, when the impact vibration is applied to the long side surface, the portion where the impact vibration can be applied is 200 mm in the casting direction. On the other hand, when striking vibration is applied to the short side surface, the portion to which the striking vibration can be imparted can be about 2300 mm in the casting direction if, for example, the length of the striking plate is sufficiently secured. Therefore, when the impact vibration is applied to the short side surface, the volume change is about 1 / 11.5.

  In the present invention, the impact vibration frequency when hitting is 4 to 12 Hz because the vibration energy is not sufficiently transmitted to the unsolidified portion of the slab when the impact vibration frequency is less than 4 Hz. Because there are few.

  From the viewpoint of applying vibration energy, it is advantageous that the frequency is large. However, when an air cylinder system is used as the vibration energy applying means, the vibration waveform is disturbed as the vibration frequency increases. Further, when the slab 1 is hit, if the vibration up to about 12 Hz is applied from the deformation characteristics of the slab, a sufficient effect can be obtained. Furthermore, when increasing the vibration frequency, it is necessary to increase the supply air pressure, and there is a concern about the influence of vibration on peripheral devices. Therefore, the upper limit of the center segregation reduction range is set to 12 Hz.

  Moreover, in this invention, vibration energy shall be 30J-150J. This is because, when vibration energy exceeding 150 J is applied, peripheral equipment installed in the continuous casting machine may be damaged. Furthermore, the addition of vibration energy more than necessary is because the durability of the striking device 6 itself is hindered.

  On the other hand, when the vibration energy is less than 30 J, the impact vibration performed from the short side surface side of the slab 1 does not sufficiently propagate to the inside of the slab near the center of the slab width direction.

The vibration energy E (J) is E = 0.5 × M × V, where M (kg) is the weight of the mold 3 and V (m / sec) is the impact speed of the mold 3 on the slab 1. ² can be obtained. Therefore, the vibration energy can be changed by changing the weight of the mold 3 or changing the collision speed of the mold 3 with the slab 1. However, the vibration frequency is particularly important since bridging at a high solid fraction can not be completely suppressed even when a large vibration energy is applied several times per minute.

  In addition, the range of the impact vibration frequency prescribed | regulated by the said invention does not change with the bloom and slab from which slab width differs. However, since the volume including unsolidified is different between bloom and slab, the optimum vibration energy changes.

Under light pressure when continuously casting using the striking vibration device of the present invention, the central solid phase ratio f _S is 0.1 to 0.1 in the range from the upstream side to the downstream side of the position where the surface of the slab 1 is hit. It is desirable to perform the slab 1 of 0.9 at a rate of 0.5 to 2.5 mm per 1 m in the length in the casting direction.

  As described above, in the present invention, even when the slab 1 is lightly reduced, the vibration due to the impact is sufficiently propagated to the inside of the slab 1 by giving the slab 1 the impact vibration that satisfies the optimum vibration condition. And a further effect of reducing segregation can be obtained.

(Example)
Hereinafter, experimental results performed to verify the present invention will be described.
Two pairs of striking devices as shown in FIG. 1 were installed in the casting direction. High carbon steels with the component ranges shown in Table 2 below were cast into blooms or slabs. The size is 250-310 mm thick and 425 mm or 2300 mm wide. The casting speed was 0.70 m / min or 0.75 m / min.

  The central solid phase ratio during light reduction was in the range of 0.1 to 0.9, and the slab was lightly reduced at a rate of 1.0 mm per 1 m length in the casting direction. As the secondary cooling, the specific water amount was unified under the condition of 0.8 liter / kg.

  Using an air cylinder type striking device, the frequency of 4 Hz or 6 Hz so that the amplitude of the vibration of the striking surface is ± 3 mm at the two short side surfaces on both sides of the slab at the position including the unsolidified part. Stroke was continuously performed at (240 times or 360 times per minute), and vibration was imparted to the slab.

  The striking conditions were a mold weight of 450 kg and a striking speed of about 0.47 m / sec or 0.71 m / sec (vibration energy was 50 J or 114 J). The shape of the contact surface with the bloom or slab of the die attached to the tip of the impacting device was about 200 mm in width in the slab thickness direction and about 1100 mm in length in the casting direction.

  In the casting test, a sample of a slab was taken, and from the position corresponding to the thickness of the cross section of the sample and the center part in the width direction, the thickness direction center part sandwiched the thickness direction 10 mm, the width direction 200 mm, A test piece of about 15 mm was taken in the casting direction.

  Using these test specimens, chips were collected from 26 locations corresponding to the center of the slab in the thickness direction with a drill blade having a diameter of 7 mm and a diameter of 2 mm, and the C content was analyzed. The ratio C / C0 obtained by dividing the analysis value C (mass%) by the C analysis value C0 (mass%) of the molten steel in the ladle is obtained, and the maximum value of these ratios (hereinafter referred to as “maximum center segregation rate”) is obtained. It was.

  The experimental conditions are shown in Table 3 below. In this experiment, the striking vibration was generated in the segment portion by the invention example (high carbon steel C) in which the striking vibration was applied between the pinch rolls by the striking vibration device of the present invention and the striking vibration device proposed in Japanese Patent Application No. 2006-53057. It performed about the comparative example (high carbon steel A) manufactured without adding the comparative example (high carbon steel B) and striking vibration.

  The experimental results are shown in FIG. When impact vibration was applied, there was no significant difference in the maximum center segregation in any case, and the maximum center segregation rates were all good at 1.15 or less. On the other hand, when no impact vibration was applied, the maximum center segregation rate sometimes exceeded 1.15 as the slab width increased. In the evaluation of the experimental results, the case where the maximum center segregation rate was 1.15 or less was evaluated as good, and the case where the maximum center segregation rate exceeded was determined as poor.

  The present invention is not limited to the above example, and it goes without saying that the embodiments may be changed as appropriate within the scope of the technical idea described in each claim.

  For example, in the above description, an air cylinder is shown as the striking device 6. However, as long as the die 3 can be driven, a hydraulic cylinder, a method using an eccentric cam, a method using a spring, etc. This method may be used.

  The present invention can be applied not only to high carbon steel slabs as shown in the examples, but also to continuous casting of other steel types such as medium carbon steel slabs and low carbon steel slabs.

Claims (1)

When continuously casting a slab having a rectangular cross section, the center solid phase ratio fs at the center of the slab thickness is in the range of at least 0.1 to 0.9 per 1 m of the casting direction length. While reducing lightly continuously so that the reduction ratio in the thickness direction is within 1%, the slab relative to at least one place where the central solid fraction f _S is in the range of 0.1 to 0.9. A device that strikes the short side surfaces on both sides continuously in the slab width direction with a striking vibration frequency of 4 to 12 Hz and a vibration energy of 30 to 150 J,
A mold that strikes the short side of the slab,
A striking device that generates periodic vibrations and transmits the vibrations to the mold;
An impact positioning device for setting a distance between the mold and the short side surface of the slab;
The mold has a structure capable of hitting the short side surface of the slab at least between two pairs of adjacent pinch rolls of a light rolling zone composed of a plurality of pinch roll pairs as a whole,
The hitting positioning device sets the distance between the tip end surface of the mold and the slab short side surface at the pull back position of the mold after detecting the pressing position of the mold to the slab short side surface, or A striking vibration device during continuous casting, wherein the striking positioning is performed in a state where a guide for setting a distance between the slab and the tip surface of the mold is pressed.

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