JPS63278655A - Light rolling reduction casting method - Google Patents

Abstract

PURPOSE:To reduce center segregation of a cast slab and to improve quality by dividing multiple pairs of rolls executing light rolling reduction to the non-solidified cast slab, measuring rolling reaction received from the cast slab and adjusting the roll reduction rate and cooling water injection rate, so as to come to the specific strain speed by grasping the strain speed of the cast slab. CONSTITUTION:At the time of applying the light rolling reduction at suitable strain speed to the cast slab 30 at the end time of solidification, the reaction (b) is acted to the divided roll 16b. The roll 16b is pushed by the cast slab 30 and detecting part of a measuring instrument 39b is deformed and the resistant value of the detecting part is changed, to generate current. This current is converted into voltage signal and inputted to a storing part of CPU40 and based on the input data of the reaction (b), the strain speed of the cast slab is calculated as a parameter. Then, the parameter is compared with the prescribed suitable strain speed and the difference is transmitted to a hydraulic control device 42 as the voltage signal. Then, the different signal is transmitted to a cooling water control device 44, too, to adjust the spray water rate injected to the divided roll 16b, so that the different signal comes to zero. Further, the reducing the rolling reduction rate of the roll 16b, the reaction (b) is relaxed, and by making the strain speed of the cast slab 30 at the suitable speed, flowing of the molten steel in the internal part of the cast slab 30 is prevented and the center segregation is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a light reduction casting method for preventing center segregation of slabs in continuous casting.

[Prior art] Normally, in continuous casting, when molten steel is cooled by a water-cooled mold, a solidified shell is formed in a thin part corresponding to the outer periphery of the slab, and the slab that has passed through the mold has unsolidified inside. While holding the molten steel, it is pulled out by pinch rolls while being guided by one layer of sabot and toe guide rolls. During the slab drawing process, spray water is injected onto the slab to promote solidification inside the slab, and when the thickness of the solidified shell grows beyond the thickness that can withstand deformation, the slab is pulled out at a predetermined curvature. While bending the slab 90 degrees, apply a light reduction blade to the solidified slab using a light reduction device. In this light reduction zone, cooling water is injected from a group of nozzles arranged in the width direction of the slab to completely solidify the slab, and then the cast slab is cast by a group of rolls of a straightening device at the end position (straightening point) of the light reduction zone. After straightening the bends in the slab, the straight slab is cut into a predetermined length using a cutting machine.

In the final solidification part of the slab (crater end), carbon (C),
Component elements such as sulfur (S), manganese (M n ), and phosphorus (P) are concentrated in the unsolidified molten steel.

Since this concentrated molten steel has a low melting point, it does not precipitate when the molten steel is stationary in the solidified shell, but when the concentrated molten steel flows in the solidified shell, it precipitates, resulting in so-called central segregation.

3 Normally, solidification shrinkage of molten steel causes the molten steel to be sucked and flow toward the bottom of the slab (in the direction of slab withdrawal), so a light reduction blade commensurate with the amount of solidification shrinkage is added to the unsolidified slab to prevent center segregation. ing.

On the other hand, when the casting speed becomes relatively high, the static pressure of the molten steel increases, and so-called bulging occurs, in which the solidified shell partially expands in areas where the reduction amount is insufficient. When bulging occurs, the expanded solidified shell is compressed by roll reduction, causing molten steel to flow toward the top of the slab (in the direction opposite to the direction in which the slab is pulled out), and concentrated molten steel precipitates at the crater end, forming a wide center. Segregation occurs. In particular, when the pitch interval of the rolls is large and when there is deflection or wear on the reduction roll,
Bulging is likely to occur. For this reason, one layer of small-diameter rolls is usually arranged in the light rolling zone to reduce the pitch between the rolls, thereby preventing the occurrence of bulging and reducing center segregation.

In the conventional light reduction casting technology, center segregation of the slab cannot be sufficiently reduced only by reduction using the light reduction device. For this reason, a rotating magnetic field or a moving magnetic field is applied to the crater end using an electromagnetic stirring device (EMS), and the concentrated molten steel at the crater end is stirred by electromagnetic induction to prevent center segregation.

[Problems to be solved by the invention] However, in the conventional light reduction casting technology, concentrated components such as [C] and [P] concentrated at the crater end are simply diffused within a certain area by electromagnetic stirring. Although it is possible to lower the peak value of the concentration of the segregated components, it is not possible to eliminate the segregation itself. For this reason, a segregation zone with an average concentration level is generated within a certain area at the center of the slab. This segregation zone contains small island-like segregation (semi-macro segregation), which causes various problems as shown below.

In recent years, demands from customers regarding the quality of steel materials have become more sophisticated and diversified, and it is necessary to further reduce the segregation of impurity elements and non-metallic inclusions that inevitably exist in manufactured steel materials. desired.

In other words, in pipe materials for oil and natural gas transportation, hydrogen-induced cracking (HIC) occurs along the central segregation zone due to the action of sour gas containing hydrogen sulfide.
There is a strong desire to prevent HIC by improving materials. It is known that HIC is likely to occur in areas where the P concentration is high in the central segregation zone, and generally, when the peak concentration of P is about 0.04% or more, the cracking occurrence rate due to HIC increases. With conventional light reduction casting technology, so-called macro-segregation occurs in the center of the slab, where the P concentration is about 10 times that of the sound part. In addition to reducing the temperature to a level of 50 ppI11 or less, the slab after solidification is soaked at about 1300°C to diffuse the segregated P and lower the maximum value of the P concentration.

Figure 9 shows the HIC of semi-macro segregated particles for various steel materials having a central segregation zone, with the horizontal axis representing the grain size of centrally segregated particles and the vertical axis representing the number of segregated particles present per 1001II11 of slab length. It is a graph diagram that investigated the influence on In the figure, black circles indicate those in which cracks occurred due to HIC, and white circles indicate those in which no cracks occurred.

As shown in this figure, for HIC generation, the particle size is approximately 0.
．． Large segregated particles of 5 m++n or larger (semi-macro segregation) are particularly harmful, and the reduction of this semi-macro segregation is the
It is known to be effective in preventing IC generation. That is,
In order to improve the HIC resistance properties of steel materials, it is necessary to reduce both the above-mentioned macro segregation and semi-macro segregation.

In addition, with respect to steel plate materials for offshore structures, there is a demand from customers mainly to improve the welding characteristics of the steel materials. In other words, if there is a central segregation zone in the steel material,
It is necessary to preheat the steel material during welding to prevent weld cracking, and after welding, the toughness of the weld heat-affected zone (HAZ) deteriorates and lamellar tear (step-like appearance that occurs along the lamination of the steel plates) occurs in the welded joint. cracks) occur. Therefore, from the viewpoint of improving the reliability of structures, it is strongly desired to reduce the central segregation zone of steel materials.

Furthermore, since segregation has a significant effect on the workability of deep-drawn steel such as beer cans, the development of segregation-free materials is strongly desired.

By the way, the amount of fluctuation of the light reduction rolls and segments during operation is kept to about 0.10 ma+ or less, but as the mechanical accuracy of each part of the equipment decreases due to long-term operation, it is necessary to apply a specified reduction blade to the slab. It becomes difficult to apply uniformly, and variations in the amount of light reduction occur in the width direction of the slab. For this reason,
There is a problem that bulging occurs, the molten steel flows, and center segregation occurs.

This invention was made in view of such circumstances, and
The purpose of the present invention is to provide a light reduction casting method capable of suppressing the flow of molten metal in an unsolidified slab due to variations in the amount of light reduction and reducing the absolute amount of impurities, etc. segregated in the center of the slab. .

[Means for Solving the Problems] The light reduction casting method according to the present invention involves injecting cooling water from a group of nozzles onto the continuously cast unsolidified slab while lightly reducing it with multiple pairs of rolls. In the light reduction casting method in which complete solidification is performed, the plurality of pairs of rolls are each divided into roll widths of a predetermined length, and the nozzle groups are arranged in the width direction of the slab along the six pairs of rolls, The roll reaction force that each split roll receives from the slab is measured, the strain rate of the slab corresponding to these roll reaction forces is determined, and the strain rate is adjusted so that these strain rates match the predetermined slab strain rate. The method is characterized in that the reduction amount of each pair of rolls to which the split roll belongs is adjusted, and the amount of cooling water sprayed from the nozzle group is increased or decreased in each region in the width direction of the slab.

[Operation] In the light reduction casting method according to the present invention, the roll reaction force that each split roll receives from each part of the slab in the middle of solidification is measured, and the strain rate of the slab corresponding to each roll reaction force is used as a parameter. grasp.

Then, the amount of reduction of each of the six pairs of rolls is adjusted, and the amount of cooling water in the nozzle group is increased or decreased in each area in the width direction of the slab.
The strain rate as a parameter is matched to a predetermined slab strain rate to prevent the flow of molten metal inside the slab. In other words, when a reaction force that exceeds the roll reaction force corresponding to a predetermined strain rate is applied to one split roll due to bulging, the rolling reduction amount of the pair of rolls to which the split roll belongs is reduced, and the split roll is The cooling of the slab is enhanced by increasing the amount of cooling water injected into the area of the rolls. When cooling is strengthened, the deformation resistance of the solidified shell increases, the strain rate acting on the slab decreases, and solidification shrinkage causes the molten metal to move in the slab drawing direction (
The fluid force sucked in the direction (toward the bottom of the slab) increases, and the fluid force in the opposite direction (towards the top of the slab) of pulling out the slab due to bulging is canceled out. On the other hand, if a reaction force lower than the roll reaction force corresponding to a predetermined strain rate is applied to one split roll, the rolling amount of the pair of rolls to which the split roll belongs is increased, and the roll reduction of the pair of rolls to which the split roll belongs is increased. Reduce cooling of the slab by reducing the amount of cooling water injected into the area. When the cooling is weakened, the deformation resistance of the solidified shell decreases, the strain rate acting on the slab increases, and the flow force that draws the molten metal in the slab drawing direction (towards the slab bottom) due to solidification contraction decreases. This counterbalances the force of pushing the molten metal back toward the top of the slab due to roll reduction, and prevents the molten metal from flowing. As a result, the actual strain rate occurring in the slab substantially matches the predetermined strain rate, and the flow of the molten metal at the final stage of solidification is prevented.

[Embodiments] Hereinafter, embodiments of the present invention will be specifically described with reference to the accompanying drawings.

First, the basic concept of center segregation reduction will be explained.

FIG. 4 is a schematic diagram showing the generation mechanism of center segregation at the final stage of solidification. In the figure, the shaded area indicates the solid phase, and the area other than the shaded area indicates the liquid phase. In addition, the symbol g in the figure is the limit solid phase ratio at which residual molten steel can flow, the symbol LI) is the thickness of the solid-liquid coexistence region, and the symbol LL is the thickness of the liquid phase region (100% liquid phase region). show. In the figure, assuming that central segregation is formed by the flowing and mixing of concentrated molten steel existing in the region from the thickness position where the solid fraction is zero to the thickness position where the solid fraction is gl. , the component concentration ratio C/Co of the molten steel at the final stage of solidification is calculated by the following equation (1).

However, each symbol in the above formula (1) is as follows.

α-LL/LD (ratio of liquid phase region to solid-liquid coexistence region at the final stage of solidification) LL, LD: Thickness of liquid phase region at the final stage of solidification, thickness of solid-liquid coexistence region g: Limit at which residual molten steel can flow The solid phase ratio Ko;
The equilibrium distribution coefficient for each component such as [C], [P], etc. in Figure 5 shows the concentration ratio C/Co of [C] obtained by the above equation (1) on the vertical axis, and the solid-liquid ratio at the final stage of solidification. The relationship between the flow of molten steel and the degree of segregation at the final stage of solidification was studied, with the horizontal axis representing the ratio α of the liquid phase region to the coexistence region. In the figure, the numbers written on each curve are the respective solid fraction g
shows. Note that the component concentration rate CL/Cθ was calculated with the equilibrium distribution coefficient Ko as O and L41. As is clear from this figure, as the flow limit solid fraction g of concentrated molten steel increases, the component concentration CL/Co increases, and as the ratio α of the completely liquid phase region decreases, the component concentration increases. The impact will be greater. That is, when the flow of concentrated molten steel becomes active, the component concentration rate increases and the degree of segregation increases. Therefore, in order to reduce center segregation, it is necessary to suppress the flow of concentrated molten steel.

As a means of suppressing the flow of this concentrated molten steel, firstly, the pitch between the rolls is narrowed to suppress the occurrence of bulging between the rolls of the slab, and secondly, the concentrated molten steel is moved toward the bottom side by solidification shrinkage. In order to prevent the slab from being sucked toward the downstream side of slab drawing, an appropriate amount of light pressure lower blade corresponding to the amount of solidification shrinkage may be applied to the slab. In addition, according to the results of actual casting tests conducted under various conditions, the effect of roll reduction of the light reduction zone is maximized when the crater end is positioned approximately 3/4 from the starting position of the light reduction zone. It turned out to be.

By the way, the inventors found that the thickness of the unsolidified region was about 30 mm.
As a result of driving studs containing a tracer (F e S) into slabs in the middle of solidification and investigating the flow condition of concentrated molten steel at the final stage of solidification by varying the amount of light reduction, the following findings were obtained. was completed.

Figure 6 shows the amount of light reduction (the amount of roll spacing reduced per 1 m of slab drawing length) on the horizontal axis, and the flow length of molten steel on the vertical axis, and the amount of light reduction and molten steel based on the above survey results. It is a graph diagram showing the relationship between flow length and the like. As is clear from this figure, the flow length of molten steel decreases as the light reduction increases, and it is confirmed that the flow length of molten steel becomes the minimum at a light reduction of approximately 1.2n+m/+++. Ta.

FIG. 1 is a schematic side view of a light reduction device used in a light reduction casting method according to an embodiment of the present invention, FIG. 2 is a perspective view showing a group of light reduction rolls, and FIG. 3 is a light reduction device. FIG. 2 is a schematic diagram showing a part of the device. A CPU (Central Processing Unit) 40 is installed in the control room of the vertical bending continuous casting machine, and controls the continuous casting operation based on various data and setting conditions detected by sensors (not shown) in various parts of the continuous casting machine. It's about to be controlled. The CPU 40 includes a storage unit that stores input data, a calculation unit that sequentially extracts data from the storage unit and performs various calculations based on a mathematical model, a comparison unit that compares the calculated value of the calculation unit with a predetermined set value, and a comparison unit. It has a command unit that transmits the result as a positive/negative voltage difference signal to each control device 42, 44 equipped with a process computer. That is, the receiving sections of the hydraulic control device 42 and the cooling water control device 44 are connected to the command section of the CPU 40, and the hydraulic control device 42 is installed in the reduction roll hydraulic system of the continuous casting machine, while the cooling water control device 44 is connected to the spray cooling system. It is installed in the water system, and the amount of roll reduction and the amount of cooling water are adjusted respectively.

On the other hand, a mold (not shown) is provided in the upper part of the continuous casting machine, and the unsolidified slab 30, which becomes a slab with a predetermined cross-sectional shape, is pulled out from the mold by pinch rolls (not shown). Below the mold, a group of support guide rolls (not shown) are arranged to surround the slab, thereby forming a vertical draw-out. A plurality of pairs of bending rolls 24 are provided below the vertical drawing section, and the bending rolls 24 bend the slab 30 during solidification so that the direction of drawing the slab is changed to horizontal.

Furthermore, a light reduction device 10 is provided below the bending rolls 24, and is configured to apply a reduction blade to the slab 30. The light reduction device 10 has two segments 12.14, each segment 12.14 having eight pairs of light reduction rolls 16.
are equipped with each.

Further, a group of spray nozzles 20 are arranged along the width of the slab 30, and each row of spray nozzles 20 is arranged between the light reduction rolls 16, and the spray nozzles 20 in each row are disposed between the light reduction rolls 16, and the spray nozzles 20 are disposed between the rolls 16 and the slab 30 from the gap between the rolls 16. Cooling water is injected into the The group of spray nozzles 20 is connected to a cooling water control device 44 that has a water volume adjustment function, and the spray volume of each row is adjusted, as well as the spray volume of the nozzles 20 belonging to each row. ing. In each row of nozzles 20, the amount of spray increases from the end region in the width direction of the slab toward the center region in the width direction of the slab.

As shown in FIG. 2, the light reduction roll 16 has a length of 3
It is divided or divided into six parts. The diameter of the light reduction roll 16 has been increased from the conventional approximately 375 mm to approximately 210 mm, and the pitch between the rolls has been increased from the conventional approximately 420 o + m to approximately 235 s + e.
In addition, the number of rolls in each segment has been changed from the conventional 5 pairs to 8 pairs. In addition, the length of the vertical drawing part in this continuous casting machine is about 4 m, the radius of curvature of the bent part of the slab is about 8 m, and the light reduction device 10
The height difference up to this point is about 1034m to 14.1m.

As shown in FIG. 3, the light reduction roll 16a, 1
6b and 16c are rotatably supported through roll chocks 17, and a rod 18 of a reduction cylinder 19 is connected to the roll chock 17. When the roll chock 17 is pushed by the rod 18, the rolls 16a, 16b, and 16c are moved to the slab 30. They are designed to be pressed against each other. Further, the reduction cylinder 19 is connected to each hydraulic pressure supply port (not shown) of the hydraulic control device 42 by a hydraulic circuit.

This hydraulic control device 42 has a pressure oil supply source (not shown). Further, a command section of the CPU 40 is connected to an operating circuit of a solenoid valve (not shown) that opens and closes each hydraulic supply port of the hydraulic control device 42. In addition, each roll 16a,
Load cells are used in bearings (not shown) that rotatably support the rolls 16 b and 16 c to absorb roll reaction force (each roll 16 a * 1 pressed against the slab 30
A roll reaction force measuring device 39 for measuring the reaction force that 6 b + 16 c receives from the slab 30 is attached to each of the roll reaction force measuring devices 39 . These measuring instruments 39 are connected to the CPU 40,
The force received from the slab 30 is converted into a voltage signal and sent to the CPU 40.
The information is sent to each

Further, a large number of nozzles 20 (only some of the - rows are shown) are arranged at predetermined intervals on the divided roll 16a.

16b, 16c, these nozzles 20
is connected to a cooling water supply port (not shown) of the cooling water control device 44. This cooling water control device 44 has a cooling water supply source (not shown).

A command section of the CPU 40 is connected to an operating circuit of a solenoid valve (not shown) that opens and closes each cooling water supply port.

When the cooling water control device 44 receives a signal from the CPU 40, each electromagnetic valve opens and closes to supply a predetermined amount of cooling water to the nozzle 20, so that the slab 30 is cooled at a predetermined cooling rate. .

Next, the case of producing slabs by the method of this invention will be specifically explained with reference to FIGS. 1 and 3. The casting steel type is Nb, V-based high tensile strength steel for in-pipe (API
-65), and the width of the slab is approximately 1950mm.
It is. Molten steel whose composition has been adjusted by RH degassing treatment and ladle refining treatment is cast into a mold from a tundish.

At this time, the temperature of the molten steel in the tandish was approximately 1552℃.
The molten steel is in a superheated state of about 33°C (the solidification temperature of this steel type is about 1519°C). When molten steel is injected into the mold, a solidified shell 32 is formed in contact with the mold wall. 0 per minute
．． The unsolidified slab 30 is pulled out at a casting speed of 75 m,
The crater end 36 is located approximately at the center of the segment 14. Further, the cooling water control device 44 adjusts the flow rate control valve of the cooling water supply source to control the amount of cooling water supplied to each spray nozzle 20, and the specific water amount o, 54. Cooling water is injected onto the slab 30 through each spray nozzle 20 in a spray pattern of e/kg (amount of spray water per 1 kg of slab).

FIG. 7 is a graph showing the relationship between strain rate and roll reaction force, with the horizontal axis representing the strain rate of the slab and the vertical axis representing the roll reaction force that the roll receives from the slab. As is clear from this figure, the strain rate and roll reaction force are in a proportional relationship with each other, and if the roll reaction force is known, the corresponding strain rate of the slab can be known. That is, there is a one-to-one correspondence between the roll reaction force and the strain rate, and for example, if the roll reaction force value detected by the roll reaction force measuring device 39 is 10 ton-f.
The strain rate at this time is 0.9 mm/min.

Now, a light reduction blade (
If a reaction force acts on the split roll 16b while applying a reduction ff1) of approximately 1.2 mm/IIl, the roll 16b is pushed by the slab 30 and the detection part of the load cell of the measuring device 39b is distorted. The resistance value of the detection section changes and a current is generated. This current is converted into a voltage signal and input to the storage section of the CPU 40. In the CPU 40, the calculation unit calculates the strain rate of the slab as a parameter based on the input data of the reaction force, compares this parameter with a predetermined appropriate strain rate, and uses the difference between the two as a voltage signal to send the command unit. via the hydraulic control device 42. At this time, a voltage difference signal is also transmitted from the command unit of the CPU 40 to the cooling water control device 44, and the amount of spray water injected to the area of the divided roll 16b is adjusted until the voltage difference signal becomes zero. In addition, the hydraulic control device 4
2, the solenoid valve of the reduction cylinder 19 is opened and closed based on the voltage difference signal from the CPU 40, and the rod 18 is moved back into the cylinder 19. As a result, the rolling reduction amount of the roll 16b is reduced, and the force of pressing the roll against the slab 30 is weakened.
The reaction force is relaxed, the strain rate of the slab 30 approaches the appropriate strain rate, and eventually the actual strain rate matches the appropriate strain rate and the voltage difference signal becomes zero. As a result, the flow of molten steel inside the slab 30 is substantially prevented, and concentrated molten steel does not precipitate at the crater end 36.

According to the above embodiment, when bulging occurs and a reaction force is applied from the slab 30 to the split rolls 16b, conventionally the roll reduction amount increases and the molten steel 34 flows toward the top of the slab, which is significant. However, since the amount of cooling water injected into the area of the split rolls 16b can be adjusted, it is possible to effectively prevent center segregation distributed in the width direction of the slab. On the other hand, when the slab strain rate decreases, the melt #A34 flows toward the bottom of the slab, but since the rod 18 can be made to protrude and the amount of reduction of the split rolls 16b can be controlled, the amount of rolling down of the split rolls 16b can be controlled. The flow of molten steel can be effectively prevented. As a result, the flow limit solid fraction g of molten steel could be reduced from the conventional 0.70 to 0.15, and the central segregation of components such as carbon could be reduced.

In addition, in the conventional light reduction casting method using electromagnetic stirring, excessive stirring occurs in unsteady parts such as the casting start part, the casting end part, or the joint part of continuous casting, and the concentration of components such as carbon is higher in the center than in the healthy part. However, according to the above embodiment, the reduction amount is adjusted for each divided roll 16 so that an appropriate strain rate is achieved over the entire area of the light reduction zone. Since precise control is possible, the quality of not only the steady portion but also the unsteady portion can be improved.

In Figure 8, the particle size distribution of semi-macro segregated particles was investigated by plotting the particle size of the segregated particles present in the segregation zone on the horizontal axis and the number of segregated particles per 100 mm of slab pulling length on the vertical axis. It is a graph diagram. In the figure, black circles represent semi-macro segregated particles present in the central segregation zone of slabs manufactured by the embodiment of the present invention, and white circles represent semi-macro segregation particles present in the central segregation zone of slabs manufactured by the conventional method. show.

As is clear from this figure, according to the embodiment of the present invention, the number of semi-macro segregated particles with a particle size of 0.5) or more, which is harmful to HIC cracking, can be significantly reduced compared to the conventional method. We were able to achieve a reduction effect.

A sample was taken from the slab manufactured according to the above example (without soaking treatment), and a corrosion test was conducted in a hydrogen sulfide atmosphere (
As a result of investigating the HIC occurrence rate on 24 cross sections using the NACE test, no cracks with a length of 0.01a+a+ or more were observed.

Furthermore, in the embodiment described above, since the diameter of the light reduction roll 16 and the pitch between the rolls are smaller than those of the prior art, the occurrence of bulging can be effectively prevented.

In addition, although the above example shows the case of manufacturing Nb, V-based high-strength steel, it is not limited to this, and can also be applied to the case of manufacturing other metal materials that exhibit hot work brittleness in a temperature range of about 800°C or less. This invention method can be used.

Furthermore, although the above embodiments have been described with reference to the case of manufacturing slabs, the method of the present invention is not limited to this, and can also be used in the case of manufacturing blooms, round billets, and the like.

[Effects of the Invention] According to the present invention, it is possible to adjust the cooling rate of the region where each divided roll is located along the width of the slab based on the reaction force that each divided roll receives from the slab; It is possible to correct the non-uniformity of the strain rate caused by variations in the amount of light reduction in the width direction of the slab.

Therefore, it is possible to effectively deal with the occurrence of bulging, and center segregation can be reduced. In addition, since the amount of roll reduction can be adjusted according to the roll reaction force measured over the entire area of the light reduction zone, it is possible to reduce the center segregation of the slab in the steady area, and also to reduce the center segregation of the slab in the unsteady area. Segregation can also be reduced. Therefore, the quality of the entire slab can be significantly improved.

[Brief explanation of the drawing]

FIG. 1 is a schematic side view of a light reduction device in which a light reduction casting method according to an embodiment of the present invention is used, FIG. 2 is a perspective view showing a group of light reduction rolls, and FIG. 3 is a light reduction device. A schematic diagram showing a part of the apparatus, FIG. 4 is a schematic diagram showing the solidification mechanism of concentrated molten steel, and FIG. 5 is a schematic diagram showing the relationship between the flow of molten steel and the degree of segregation.
Fig. 6 is a graph showing the relationship between light reduction amount and molten steel flow length, Fig. 7 is a graph showing the relationship between roll reaction force and strain rate, and Fig. 8 is a graph showing the effect of this invention. , No. 9
The figure is a graph showing the influence of semi-macro segregation on hydrogen-induced cracking (HIC). 10; light reduction device, 16; light reduction roll, 19; reduction cylinder, 30; slab, 32; solidified shell, 34; molten steel, 36
; Crater end, 39; Roll reaction force a'I11 regulator,
40; CPU, 42; Hydraulic II Ja equipment
ll, 44; Cooling water control device. Applicant's representative Patent attorney Takehiko Suzue Figure 3 Figure 1 Figure 4 α Figure 5 Figure 6 ffl 閂禮 [2111孝j-Icloud (mm) Fig. 9

Claims (1)

[Claims] In the light reduction casting method, a continuously cast unsolidified slab is lightly rolled down by a large number of pairs of rolls, and cooling water is injected onto the slab from a nozzle group to completely solidify it. The nozzle groups are each divided into roll widths, and each nozzle group is arranged in the slab width direction along each pair of rolls.The roll reaction force that each divided roll receives from the slab is measured, and these roll reaction forces are measured. The strain rate of the slab corresponding to each is determined, and the rolling reduction amount of each pair of rolls to which the split roll belongs is adjusted so that these strain rates match the predetermined slab strain rate, and the nozzle group is cooled. A light reduction casting method characterized by increasing or decreasing the amount of water sprayed in each region in the width direction of the slab.