EP2349612B1 - Method and continuous casting plant for manufacturing thick slabs - Google Patents

Description

Technical area

The invention relates to a method for producing thick steel slabs with a casting thickness exceeding 360 mm and a casting width exceeding 1000 mm in a continuous casting plant. Furthermore, the invention relates to a continuous casting plant for carrying out this method.

The casting of steel strands in continuous casting plants, in which the cast steel strand is first bent after its exit from the continuous casting mold in a downstream strand guide and then straightened again, becomes increasingly more difficult with increasing strand thickness. The tensile and compressive stresses occurring in the strand shell during the deformation process lead to crack formation in the strand edge and surface region of the steel strand. So far, there are only a few continuous casting plants, with which steel strands with strand thicknesses over 360 mm poured and slabs can be produced in this thickness range.

At present, there is an increasing demand for slabs in a thickness range of 360 to 450 mm for the subsequent production of correspondingly thick heavy plates on the part of the processing industry.

State of the art

A continuous casting plant of the type "vertical plant or vertical turning plant", which has a long vertical strand guide part with subsequent bending and straightening zone, is from the publication of Dr.-Ing. Klaus Harste et al; "Construction of a new vertical caster at Dillinger metallurgical works"; MPT International 4/1998; Pp. 112-122 already known. This casting plant, whose layout is shown in Figure 8, allows the casting of steel strands with a casting widths of 1400 to 2200 mm and a casting thickness between 230 and 400 mm. It has a very long vertical strand guide with cooling equipment for intensive strand cooling in this section to allow subsequent bending and straightening of the steel strand with solidified strand. This plant concept leads to a large construction height of the continuous casting plant of about 45 m and thus to high investment costs, especially in the necessary infrastructure and to difficult maintenance conditions. For casting thicknesses of 400 mm, the achievable Casting speed about 0.3 m / min, whereby the productivity per strand is relatively low. However, the low casting speed also means that the cast steel strand can not be kept hot enough for straightening and therefore must be kept below a critical temperature with intensive cooling to avoid Ductility problems that typically occur in temperature ranges of 600 to 850 ° C.

From the DE 31 12 947 A1 already a Bogenstranggießanlage for casting a steel strand with a lying in a thickness range of 200 to 300 mm strand thickness is known with which slabs can be produced in good quality. The shaping of the metal strand takes place in this Bogenstranggießanlage in a curved mold with a radius of curvature which is in a range of 2.0 to 4.9 m and which corresponds to the radius of curvature in a first zone of the subsequent strand guide. In a subsequent very long straightening zone, the steel strand is again straightened, forcibly leading to the formation of a trapezoidal cross-section of the steel strand. This cross-sectional distortion is greater, the greater the strand thickness and the smaller the radius of curvature in the arc mold and leads to quality problems in the subsequent rolling in the plate mill.

From the publication
Siemens: "First Ultra Thick Slab Caster in China - Siemens to Supply Shougang Qinhuangdao Works with Caster Capable of Casting 400-mm Thick Slabs" Aug 13, 2008 (2008-08-13), pp. 1-2 , XP002565642,
For example, it is known to cast a steel strand having a thickness of 400 mm through a straight die continuous casting machine. How an ultra-thick slab can be poured through a curved mold is not apparent from this document.

Presentation of the invention

The object of the present invention is therefore to avoid the disadvantages of the known prior art and to propose a method for the production of thick steel slabs and a continuous casting plant for carrying out this process, wherein the production of high-quality steel strands and slabs in a 360 mm bordering Casting thickness with good internal quality, low susceptibility to cracking and extensive Formathaltigkeit is guaranteed.

Another object of the invention is to keep the investment and operating costs low with high productivity of the casting plant.

• Gießen eines Stahlstranges mit noch flüssigem Kern in einer Bogenkokille mit einem zumindest über einen Teilbereich seiner Längserstreckung ausgangsseitig gekrümmt ausgerichteten Kokillenformhohlraum, wobei der gegossene Stahlstrang die Bogenkokille gekrümmt mit einem aufgeprägten Kokillen-Bogenradius verlässt,
• Umlenken des gegossenen Stahlstranges von einer durch den Kokillen-Bogenradius bestimmten Gießrichtung in eine horizontale Transportrichtung und Stützen und Führen des Stahlstranges in einer Strangführung, die sich vom Austritt des Stahlstranges aus der Bogenkokille bis zum Eintritt in eine Zerteileinrichtung erstreckt,
• Führen des Stahlstranges in einer Kreisbogenführung der Strangführung auf einem Strangführungs-Bogenradius von 9,0 bis 15,0 m,
• Rückbiegen des gegossenen Stahlstranges von dem Strangführungs-Bogenradius auf einen geraden Stahlstrang bei noch flüssigem bzw. teilflüssigem Kern in einer Richtzone innerhalb der Strangführung,
• kontinuierliches Kühlen des gegossenen Stahlstranges in der Strangführung, wobei das Kühlen des gegossenen Stahlstranges geregelt durch Aufbringen von Kühlmittel auf die Breitseiten des gegossenen Stahlstranges mit einer Kühleinrichtung in der Strangführung erfolgt,
• Halten der Oberflächentemperatur des Stahlstranges in die Richtzone der Strangführung über dem Duktilitätstief der jeweiligen Stahlsorte,
• Halten des Anteils der festen Strangschale des gegossenen Stahlstranges bei maximal 95% der halben Strangdicke während der Phase des Rückbiegens in der Richtzone,
• Zerteilen des Stahlstranges auf Brammen vorbestimmter Länge in einer Zerteileinrichtung.

The object underlying the invention is achieved in a method for producing thick steel slabs with a casting thickness exceeding 360 mm and a casting width exceeding 1000 mm by the combination of the following features:

• Casting a steel strand with a still liquid core in a curved mold with a mold cavity aligned on the output side curved over at least part of its longitudinal extension, the cast steel strand leaving the curved mold curved with an impressed mold arc radius,
• Deflecting the cast steel strand from a casting direction determined by the mold arc radius in a horizontal transport direction and supporting and guiding the steel strand in a strand guide extending from the exit of the steel strand from the arc mold until entry into a dicing device;
• Guiding the steel strand in a circular guide of the strand guide on a strand guide arc radius of 9.0 to 15.0 m,
• Bending back the cast steel strand from the strand guide arc radius to a straight steel strand with the liquid or semi-liquid core in a straightening zone within the strand guide,
• continuous cooling of the cast steel strand in the strand guide, wherein the cooling of the cast steel strand is controlled by applying coolant to the broad sides of the cast steel strand with a cooling device in the strand guide,
• Maintaining the surface temperature of the steel strand in the straightening zone of the strand guide above the ductility depth of the respective steel grade,
• Maintaining the proportion of the solid strand shell of the cast steel strand at a maximum of 95% of the half strand thickness during the phase of re-bending in the straightening zone,
• Cutting the steel strand on slabs of predetermined length in a dicing device.

Because of its curved shape and the resulting reduced vertical length, a curved mold does not have the conditions, which are known from a straight mold, for introducing the steel melt into the mold and for uniform strand shell formation. However, in contrast to a straight mold, the need for a strand bend in a bending zone immediately after or at a short distance from the mold can be largely or completely avoided. The risk of cracking in the edge or surface area of the strand is thereby reduced.

Furthermore, a system with curved mold compared to a plant with a straight mold at the same strand guide radius of curvature on a lower height.

The arc mold used in the proposed method may be formed with a straight inlet section and a curved outlet section, wherein the outlet section has a curvature corresponding to a predetermined mold bending radius. Alternatively, the mold cavity of the curved mold can also be continuously curved with a constant mold radius of curvature. Variations of these embodiments are possible.

When the mold bow radius of the cast steel strand at the exit from the arc mold corresponds to the strand guide arc radius of the circular arc guide in the strand guide, the cast steel strand is freely transferred from the arc mold into the arc guide of the strand guide.

Favorable production conditions for a cast steel strand or for slabs having a casting thickness exceeding 360 mm, in particular at a casting thickness in a thickness range of 360 to 450 mm, are achieved when the cast steel strand in the arc mold with a Kokillen- arc radius between 9.0 m and 15.0 m is generated, is held in a subsequent circular arc guide the strand guide on this radius of curvature without further deformation and in a subsequent straightening zone within the strand guide of a radius of curvature (R) between 9.0 m and 15.0 m straightened again.

In an alternative embodiment, the mold radius of curvature of the cast steel strand as it exits the arc mold may be greater or less than the strand guide arc radius in the strand guide and the cast steel strand in a bend zone within the strand guide from the mold arc radius of the cast steel strand as it exits the strand Curved mold can be bent to the strand guide arc radius in the strand guide. This embodiment makes it possible to hold the cast steel strand after its exit from the arch mold with the curvature impressed on it, which corresponds to the Kokillenausgangsseitigen Kokillen arc radius constant over a certain distance and then make a strand bend on the strand guide arc radius within a bending zone or make this bending process immediately after the exit of the steel strand from the Bogenkokille. In any case, the bending process is kept low even with low strand shell thickness.

The bending of the cast steel strand to a predetermined radius of curvature in a bending zone and the bending back of the cast steel strand in a straightening zone corresponds to the concept of known continuous slab casters and has proven itself as such. Essential for the casting of thick slabs is that both processes take place at times at which the steel strand still has a liquid or partially liquid core, or it is necessary to regulate the cooling of the steel strand in the strand guide accordingly. With increasing strand thickness, the requirements for the most uniform possible cooling, which must necessarily be reflected in a uniform over the strand length and strand width temperature distribution at high temperature level in order to ensure a uniform elasticity of the strand and to avoid cracking due to temperature differences.

The desired and the system control predetermined temperature profile is determined by an inlet surface temperature of the steel strand in the straightening zone of the strand guide. Thus, the steel strand including the surface area should be kept in a temperature range which is above the ductility low, whereby the tendency to form surface cracks is also minimized.

A plant with a bow mold has a lower strand length from the casting level to the straightening zone in comparison with a plant with a straight die at the same strand guide arc radius. Therefore, the time it takes the strand for the same casting speed for this route, shorter than in a comparable system with a straight mold. Due to the shorter time available for cooling, it is possible to keep the surface temperature at a comparatively higher level. This minimizes the tendency to form surface cracks.

Suitably, the proportion of the solid strand shell of the cast steel strand amounts to a maximum of 95% of half the strand thickness during the phase of re-bending in the straightening zone.

According to an expedient further development, through a reduction in the thickness of the steel strand using soft reduction or dynamic soft reduction, mixing of the preferably partially solidified core zone near the through solidification point of the strand is aimed for, thus achieving an improved microstructure in the core region of the slab and approaches to line separations and porosities avoided. Accordingly, a soft-reduction, in particular a dynamic soft-reduction, is applied to the cast steel strand in a still liquid or semi-liquid core region of the steel strand with a strand guide roll adjusting device.

According to an expedient development of the invention, the cast steel strand is bent in a bending zone within the strand guide to a radius of curvature between 9.0 m and 15.0 m, held in a subsequent circular arc guide the strand guide on this radius of curvature without further deformation and in a subsequent straightening zone within the strand guide, starting from an arc radius between 9.0 m and 15.0 m straightened again. Especially for casting thicknesses of between 360 and 450 mm, this radius of curvature, while providing the most accurate possible cooling in these areas of the strand guide, provides the best surface quality and minimizes cracking on the cast steel strand.

After an expedient development of the invention, the impact position of the coolant jets on the cooling of the cast steel strand Steel strand at least in a portion of the strand guide on the basis of a continuous determination of the temperature profile along the transport path of the steel strand and regulated in normal planes thereto.

Suitably, the amount of coolant applied to the steel strand in the strand guide until it enters the straightening zone is regulated as a function of a predetermined temperature profile along the transport path of the steel strand and in a normal plane. This is intended to achieve a further increase in the accuracy of the temperature distribution over the steel strand surface. The given temperature profile takes into account the ductility characteristics of the steel grade to be cast.

Further stabilization of the cooling conditions is achieved if the controlled cooling of the cast steel strand takes place after the dry operation within the strand guide with the inclusion of peripherally cooled strand guide rolls. Here, the need to consider the cooling of the strand guide rollers as an essential element in the measurement of the intensity of the coolant application, or to align the intensity of the coolant application in individual areas according to the needs of the strand guide rollers, avoided. This means that the strand surface temperature can be kept at a very high level, at least in the region up to the bending back of the steel strand. The cooling of the strand guide rollers takes place here almost exclusively by an internal cooling of the strand guide rollers, wherein the coolant is suitably guided in the roller sheath region as close as possible to the roller sheath surface through coolant channels.

In order to optimize the deposition rate of non-metallic elements, for example cast powder particles, in the region of the mold and just below, it is advantageous if the flow movement of the molten steel of the liquid core of the steel strand in the mold or in the region of the strand guide is influenced by an electromagnetic device. In addition to an increased rise of the non-metallic impurities to the bath level surface in the mold, there is a targeted mixing of the molten steel and to reduce segregation tendencies. Preferably, the method described is used for producing thick steel strands when the steel strand is cast with a casting thickness lying in a thickness range of 360 mm to 450 mm.

• eine Bogenkokille mit einem zumindest über einen Teilbereich seiner Längserstreckung ausgangsseitig gekrümmt ausgerichteten Kokillenformhohlraum mit einem ausgangsseitigen Kokillen-Bogenradius zum Herstellen eines Stahlstranges mit einem flüssigen Kern,
• eine Strangführung zum Stützen und Führen des gegossenen Metallstranges von einer durch den Kokillen-Bogenradius bestimmten Gießrichtung in eine horizontale Transportrichtung, die sich von der Kokille bis zu einer Zerteileinrichtung erstreckt,
• eine Kreisbogenführung innerhalb der Strangführung zum Führen des Stahlstranges auf einem Strangführungs-Bogenradius von 9,0 bis 15,0 m,
• eine Richtzone innerhalb der Strangführung zum Rückbiegen des gegossenen Stranges von dem Strangführungs-Bogenradius auf einen geraden Stahlstrang bei noch flüssigem bzw. teilflüssigem Kern,
• eine Kühleinrichtung in der Strangführung zum kontinuierlichen, geregelten Kühlen des Stahlstranges, die mit einer zentralen Recheneinheit verbunden und von dieser gesteuert ist und in der ein mathematisches Modell zur kontinuierlichen Ermittlung des Temperaturprofils entlang des Transportweges des Stahlstranges und in Normalebenen dazu hinterlegt ist,
• eine Zerteileinrichtung zum Zerteilen des Stahlstranges auf Brammen vorbestimmter Länge.

The object stated in the introduction is achieved in a continuous casting plant for the production of thick steel slabs with a casting thickness exceeding 360 mm, preferably at a casting thickness of 360 mm to 450 mm and a casting width exceeding 1000 mm, by the combination of the following features:

• a curved mold having a mold cavity which is curved on the output side at least over a partial region of its longitudinal extent and having an output-side mold arc radius for producing a steel strand with a liquid core,
• a strand guide for supporting and guiding the cast metal strand from a casting direction determined by the Kokillen arc radius in a horizontal transport direction, which extends from the mold to a dicing device,
• a circular arc guide within the strand guide for guiding the steel strand on a strand guide arc radius of 9.0 to 15.0 m,
• a straightening zone within the strand guide for bending back the cast strand from the strand guiding arc radius to a straight steel strand with the liquid or semi-liquid core,
• a cooling device in the strand guide for the continuous, controlled cooling of the steel strand, which is connected to and controlled by a central processing unit and in which a mathematical model for continuously determining the temperature profile along the transport path of the steel strand and deposited in normal planes,
• a dicing device for cutting the steel strand on slabs of predetermined length.

Essential in a continuous casting plant of this type is the combination of a curved mold with a downstream strand guide, with a circular arc guide and with a straightening zone, in conjunction with a cooling device for controlled cooling of the steel strand shaping, transporting and straightening the cast steel strand at liquid core and high quality requirements of the ensures cast steel strand or slabs in the claimed thickness range.

Bending stresses of the strand shell of the curved mold steel strand are avoided when the output side mold arc radius of the arc mold corresponds to the strand guide arc radius of the circular arc guide within the strand guide.

An optimization of metallurgical requirements and investment and operating costs of the casting plant for the production of a cast steel strand or slabs with a 360 mm casting thickness, in particular at a casting thickness in a thickness range of 360 to 450 mm, are achieved when the strand guide arc radius of Circular arc guide within the strand guide is 9.0 to 15.0 m. Accordingly, the selected value of the mold arc radius corresponds to the selected value of the strand guide arc radius within this preferred range.

According to a further embodiment of the curved mold, the output side mold arc radius is greater or smaller than the strand guide arc radius of the circular arc guide within the strand guide. Subsequent to the arc mold, a bending zone is disposed within the strand guide for bending the cast steel strand to a predetermined strand guide arc radius while the core is still liquid.

An optimization of metallurgical requirements and investment and operating costs of the casting machine result in this embodiment, when the output side Kokillen-arc radius of the arc mold is 8.0 to 20.0 m, with the exception of the set value for the strand guide arc radius and the strand guide arc radius the circular arc guide within the strand guide is 9.0 to 15.0 m.

In both cases, the overall height of the casting plant remains low and the quality specifications that are standard for cast steel strands with, for example, 200-250 mm casting thickness are almost reached.

The cooling device in the strand guide is equipped with several independently controllable cooling zones over the casting width and / or with height-adjustable spray nozzles with controllable adjusting devices. This is a targeted influencing the strand edge temperature by a width-dependent control of the amount of cooling water and / or a change in the distance of the spray nozzles from the steel strand surface and thus a change in the lateral distance of the coolant jet from the steel strand edge possible.

One or more electromagnetic devices, such as a stirring coil, for influencing the flow motion of the molten steel of the liquid core of the steel strand are arranged in the mold or in the region of the curved strand guide.

Advantageously, peripherally cooled strand guide rollers are arranged in the strand guide for supporting and guiding the steel strand. By using these peripherally cooled strand guide rollers, there is a significant decoupling of the different cooling requirements of the cast metal strand and the strand guide rollers, which are in direct line contact with the hot steel strand and its radiant heat are exposed.

Brief description of the drawings

Fig. 1

einen Längsschnitt durch eine erfindungsgemäße Stranggießanlage nach einer ersten Ausführungsform,

Fig. 2

einen Längsschnitt durch eine erfindungsgemäße Stranggießanlage nach einer zweiten Ausführungsform,

Fig. 3

die Anordnung von Spritzdüsen einer Kühleinrichtung in einer Strangführung,

Fig. 4

eine weitere Ausführungsform der Kühleinrichtung mit unabhängig regelbaren Kühlzonen.

Further advantages and features of the present invention will become apparent from the following description of non-limiting embodiments, reference being made to the following figures, which show:

Fig. 1

a longitudinal section through a continuous casting plant according to the invention according to a first embodiment,

Fig. 2

a longitudinal section through a continuous casting plant according to the invention according to a second embodiment,

Fig. 3

the arrangement of spray nozzles of a cooling device in a strand guide,

Fig. 4

a further embodiment of the cooling device with independently controllable cooling zones.

Embodiment of the invention

In FIG. 1 is a schematic longitudinal section of the structural design of a continuous casting plant for producing slabs of liquid steel for a casting thickness of 400 mm illustrated.

The continuous casting plant has a curved mold 1 with a curved aligned mold cavity 1a. It is designed as an oscillating, internally cooled Verstellkokille with broad side walls and narrow side walls and allows the casting of steel strands with different strand width and possibly also different strand thickness. The mold 1 is equipped with an electromagnetic device 2, such as a stirring coil or an electromagnetic brake, for influencing the flow motion of the molten steel in the liquid core of the cast steel strand.

To the mold 1 includes a strand guide 3, which extends to a cutting machine designed as a cutting device 4 for cutting the steel strand in slabs. In the strand guide, the cast steel strand is supported and guided on its broad side walls in a tight corset of driven and non-driven strand guide rollers 5 and redirected from a casting direction G determined by the Kokillen-Bogenradius RK in a horizontal transport direction T. Groups of both sides of the steel strand arranged strand guide rollers 5 are summarized in strand guide segments 6.

The strand guide 3 comprises a series of successive sections with specific functions, the structure of which is essentially known. The emerging from the mold 1 steel strand is transported without application of bending stresses along a circular arc with the strand guide arc radius RSt in a circular arc guide 9 and while maintaining this radius of curvature. The strand guide radius of curvature RSt here corresponds to the mold arc radius RK, whereby the Biegebelastungsfreie transport is guaranteed. In a first section of the strand guide 3, immediately after the curved mold 1, in addition, a strand support with strand guide rollers 5 also takes place on the narrow sides of the steel strand. In one of the circular arc guide 9 subsequent straightening zone 10 is a bending back and straightening of the steel strand. Subsequently, the steel strand is conveyed in a horizontal strand guide 11 to the dividing device 4.

This structural design can be supplemented by various additional devices not shown and not described between and within the described sections of the strand guide, without thereby departing from the scope of the claims.

A possible further embodiment of the continuous casting plant according to the invention is in FIG. 2 shown. Again, the strand guide 3 comprises a series of successive sections with specific functions. In a curved strand support device 7 emerging from the sheet mold 1 steel strand is performed and supported without applying bending stresses according to the Kokillen-Bogenradius RK. In a first region of the strand support device 7, a strand support with strand guide rollers 5 also takes place on the narrow sides of the steel strand. In a subsequent bending zone 8, a progressive bending of the steel strand from mold arc radius RK to the strand guiding arc radius RSt of the subsequent circular arc guide 9 takes place. In the circular arc guide 9, the steel strand is transported while maintaining the strand guiding arc radius. The further transport of the steel strand is analogous to the embodiment according to FIG. 1 ,

In the strand guide 3, the steel strand is subjected with its indicated by dashed lines liquid core of a controlled cooling. The cooling device 12 comprises, as in the FIGS. 3 and 4 shown, between the strand guide rollers 5 positionable spray nozzles 13, which are independently controllable in a normal plane N to the transport direction T at least in some areas. In each cooling zone Z over the casting width B are corresponding to the FIG. 3 height-adjustable spray nozzles 13 with associated adjusting devices 14, or as in FIG. 4 shown, spray nozzles 13 provided with control valves 18 for controlling the amount of water. The Adjustment devices 14 or the control valves 18 are actuated by a computing unit 15.

One or more of the strand guide segments 6, which are arranged between the straightening zone 10 and the dividing device 4, are associated with special positioning devices 17 for strand guide rollers 5. These segments form a soft reduction zone 16. The strand guide rollers in these segments can be wedge-shaped to the steel strand and thus allow a small reduction in the thickness of the metal strand and an improvement of the metallurgical properties in the core zone of the steel strand.

LIST OF REFERENCE NUMBERS

1

curved mold

1a

Kokillenformhohlraum

2

electromagnetic device

3

strand guide

4

Zerteileinrichtung

5

Strand guide rolls

6

Strand guide segment

7

Strand support means

8th

bending zone

9

Circular arc guide

10

straightening zone

11

Horizontal strand guide

12

cooling device

13

spray nozzles

14

Adjustment device for spray nozzles

15

computer unit

16

Soft Reduction Zone

17

Adjustment devices for strand guide rollers

18

control valves

RK

Mold arc radius

RSt

Strand guide arc radius

G

casting

T

transport direction

Z

cooling zone

B

casting width

Claims (21)

1. Method for manufacturing thick slabs of steel with a cast thickness exceeding 360 mm and a cast width exceeding 1,000 mm in a continuous casting plant, characterized by the combination of the following features:

   - casting a steel strand having a core which is still liquid in a bow-type mold (1) with a mold cavity (1a) which is oriented so as to be curved on the output side at least over a partial region of its longitudinal extent, the cast steel strand leaving the bow-type mold in curved form with an impressed mold arc radius (RK),

   - deflecting the cast steel strand from a casting direction determined by the mold arc radius (RK) to a horizontal direction of transportation and supporting and guiding the steel strand in a strand guide (3) which extends from the point at which the steel strand issues from the bow-type mold to the point at which it enters a divining means (4),

   - guiding the steel strand in a circular arc guide (9) of the strand guide (3) on a strand guide arc radios (RSt) of 9.0 to 15.0 m,

   - bending the cast steel strand back from the strand guide arc radius (RSt) to a straight steel strand while the core is still liquid or partially liquid in a straightening zone (10) within the strand guide (3),

   - continuously cooling the cast steel strand in the strand guide (3), the cast steel strand being cooled in a regulated manner by applying coolant to the wide sides of the cast steel strand using a cooling means (12) in the strand guide (3),

   - maintaining the surface temperature of the steel strand in the straightening zone (10) of the strand guide (3) above the ductility trough of the respective grade of steel,

   - maintaining the proportion of the solid strand shell of the cast steel strand at at most 95% of half the strand thickness during the bending-back phase in the straightening zone (10),

   - dividing the steel strand into slabs of predetermined length in a dividing means (4).
2. Method according to claim 1, characterized in that the cast steel strand is passed from the bow-type mold to the strand guide without bending forces, the mold arc radius (RK) of the cast steel strand corresponding, at the point at which the steel strand issues from the bow-type mold, to the strand guide arc radius (RSt) in the strand guide (3).
3. Method according to claim 2, characterised in that the cast steel strand is produced in the bow-type mold with a mold arc radius (RK) between 9.0 m and 15.0 m, is maintained in a subsequent circular arc guide (9) of the strand guide at this arc radius without further deformation and is restraightened in a subsequent straightening zone (10) within the strand guide (3) from an arc radius (R) between 9.0 m and 15.0 m.
4. Method according to claim 1, characterized in that the mold arc radius (RK) of the cast steel strand is greater or less, at the point at which the steel strand issues from the bow-type mold, than the strand guide arc radius (RSt) in the strand guide (3) and the cast steel strand is bent, in a bending zone (8) within the strand guide (3), from the mold arc radius (RK) of the cast steel strand, at the point at which the steel strand issues from the bow-type mold, to the strand guide arc radius (RSt) in the strand guide (3).
5. Method according to claim 4, characterized in that the cast steel strand is bent, in the bending zone (8) within the strand guide (3), to an arc radius (R) between 9.0 m and 15.0 m, is maintained in a subsequent circular arc guide (9) of the strand guide (3) at this arc radius without further deformation and is restraightened in a subsequent straightening zone (10) within the strand guide (3) from an arc radius (R) between 9.0 m and 15.0 m.
6. Method according to one of the preceding claims, characterized in that, during the cooling of the cast steel strand, the position in which the jets of coolant strike the steel strand is regulated on the basis of a continuous determination of the temperature profile along the path of transportation of the steel strand and in planes normal thereto.
7. Method according to one of the preceding claims, characterized in that the amount of coolant that is applied to the steel strand in the strand guide (3) until the steel strand leaves the straightening zone (10) is regulated as a function of a predefined temperature profile in consideration of the ductility properties of the respective grade of steel along the path of transportation of the steel strand and in a plane normal thereto.
8. Method according to one of the preceding claims, characterized in that the cast steel strand is cooled in a regulated manner after dry operation involving peripherally cooled strand guide rolls (5).
9. Method according to one of the preceding claims, characterized in that a soft reduction, in particular a dynamic soft reduction, is applied to the cast steel strand in a region with a steel strand core which is still liquid or partially liquid using a device for attaching strand guide rolls (17).
10. Method according to one of the preceding claims, characterized in that the flow movement of the steel melt of the liquid core of the steel strand is influenced by an electromagnetic means (2) in the mold (1) or in the subsequent region of the vertical guide of the steel strand.
11. Method according to one of the preceding claims, characterised in that the steel strand is cast with a cast thickness of up to 450 mm.
12. Method according to one of the preceding claims, characterized in that the steel strand is cast at a casting speed between 0.5 and 1.0 m/min.
13. Continuous casting plant for manufacturing thick slabs of steel with a cast thickness exceeding 360 mm and a cast width exceeding 1,000 mm, characterized by the combination of the following features:

    - a bow-type mold (1) with a mold cavity (1a) which is oriented so as to be curved on the output side at least over a partial region of its longitudinal extent and has an output-side mold arc radius (RK) for manufacturing a steel strand having a liquid core,

    - a strand guide (3) for supporting and guiding the cast metal strand from a casting direction determined by the mold arc radius (RK) to a horizontal direction of transportation extending from the mold (1) up to a dividing means (4),

    - a circular arc guide (9) within the strand guide (3) for guiding the steel strand on a strand guide arc radius (RSt) of 9.0 to 15.0 m,

    - a straightening zone (10) within the strand guide (3) for bending the cast strand back from the strand guide arc radius (RSt) to a straight steel strand while the core is still liquid or partially liquid,

    - a cooling means (12) in the strand guide (3) for continuously cooling the steel strand in a regulated manner, the cooling means being connected to and controlled by a central computing unit (15) in which a mathematical model is filed for continuously determining the temperature profile along the path of transportation of the steel strand and in planes normal thereto,

    - a dividing means (4) for dividing the steel strand into slabs of predetermined length.
14. Continuous casting plant according to claim 13, characterized in that the output-side mold arc radius (RK) of the bow-type mold corresponds to the strand guide arc radius (RSt) of the circular arc guide within the strand guide.
15. Continuous casting plant according to claim 13, characterized in that the output-side mold arc radius (RK) is greater or less than the strand guide arc radius (RSt) of the circular arc guide within the strand guide and in that, following the bow-type mold, a bending zone (8) is arranged within the strand guide for bending the cast steel strand to the strand guide arc radius (RSt) while the core is still liquid.
16. Continuous casting plant according to claim 15, characterised in that the output-side mold arc radius (RK) of the bow-type mold is 8.0 to 20.0 m not including the defined value for the strand guide arc radius (RSt) and the strand guide arc radius (RSt) of the circular arc guide within the strand guide (3) is 9.0 to 15.0 m.
17. Continuous casting plant according to one of claims 13 to 16, characterized in that the cooling means (12) in the strand guide is equipped with a plurality of cooling zones (Z), which can be regulated independently of one another, over the cast with (B).
18. Continuous casting plant according to one of claims 13 to 17, characterized in that the cooling means (12) in the strand guide (3) are equipped with height-adjustable spray nozzles (13) and activatable adjusting means (14).
19. Continuous casting plant according to one of claims 13 to 18, characterized in that an electromagnetic means (2) for influencing the flow movement of the steel melt of the liquid core of the steel strand is arranged in the mold (1) or in a strand support means (7) in the region of the vertical guide of the steel strand.
20. Continuous casting plant according to one of claims 13 to 19, characterized in that peripherally cooled strand guide rolls (5) are arranged in the strand guide (3) for supporting and guiding the steel strand.
21. Continuous casting plant according to one of claims 13 to 20, characterized in that at least one strand guide segment (6) is equipped with a regulatable means for attaching strand guide rolls (17) for carrying out a soft reduction, in particular a dynamic soft reduction, on the steel strand between the straightening zone (10) and the divining means (4) in a region with a steel strand core which is still liquid or partially liquid.

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