EP3184202B1 - Method for continuously casting a metal strand - Google Patents

Description

The invention is directed to a method for producing a metal strand, in particular a steel strand comprising the casting of a molten metal, in particular molten steel, in a continuous casting process to a casting strand, which is cooled with coolant and, if desired, reduced in thickness, based on one or more of the time-dependent temperature distribution over the cast strand length and / or the formation of a desired structure of the cast strand over the cast strand length descriptive and / or calculating simulation and computational models, in particular the so-called DSC ( D ynamic S olidification C ontrol) calculation and control program, constantly during the production of Gießstrangs values be considered, which describe the formation of the respective microstructure composition and / or this or the cast strand training influencing process parameters and based on which online dynamically during the production d It is cast strand cooling the casting strand and / or the casting speed is adjusted. Furthermore, the invention is directed to a casting strand obtained by such a process.

When casting a molten steel in a continuous casting the temperature of the cast strand obtained during solidification at each cross-sectional position of the cast strand during the production of the analysis dependent about 1,550 ° C amounting casting temperature drops below 900 ° C, sometimes below 700 ° C. The ductility of the steel material used, which is an evaluation criterion for the weakening of the material, has local minima in this temperature interval. When carrying out the casting process, special emphasis is therefore placed on the temperature control and this selected and adjusted so that in the crack-critical bending and Ranges of a continuous caster in the production of the cast strand ductility is high enough to avoid cracks.

This has been achieved by the fact that the cast strand is cooled in the so-called hot driving only with little splash water as the cooling medium. This ensures that the temperatures during the production of the cast strand remain so high that the otherwise due to forming precipitates in the steel structure occurring Ductility drop does not occur. Alternatively, another way of reducing or avoiding the drop in ductility is to very strongly cool the steel during the production of the cast strand, to such an extent that the steel has already completed the conversion of γ-iron into α-iron, if it does enters the crack-critical bending and straightening area of a continuous casting plant. This procedure with intensive cooling of the cast strand obtained has the advantage that due to the low temperatures to reduce the spread of the cast strand obtained and on the narrow sides of the cast strand obtained to reduce the bulge.

There is also the risk that ferrite grains on the austenite grain boundaries form in the formation of low ferrite fractions in the self-adjusting microstructure, which is the case, for example, when ferrite spaces with a volume fraction of 5% to 40% form on the surface side settle, which in turn leads to an increased risk for the formation of cracks in the cast strand.

Furthermore, during the cooling of the cast strand, the problem arises that, in the case of uneven cooling, for example, one of the narrow sides of the resulting cast strand, in a cross section of the cast strand, it may be possible to produce non-uniform structural parts. Since ferrite has a lower density and thus a larger specific volume than austenite, the respective steel material expands when converting austenite into ferrite different strong. If there is now an uneven cooling of Gießstrangquerschnittes, different ferrite shares and different voltages over the course of a narrow side of the cast strand. This may, in turn, if necessary, lead to cracks, in particular if additional external stresses, such as, for example, the bending of the cast strand in the bending or straightening area of a continuous casting plant, are added.

From the DE 10 2012 224 502 A1 a simulation and calculation model is known, by means of which it is possible to calculate and adjust ZTU (time-temperature-conversion) diagrams or diagrams when rolling metallic rolling stock, and in particular when rolling steel in a hot strip mill or a heavy plate mill To predict structure compositions. The basis of this simulation and calculation model is a temperature calculation model in which, among other things, the dynamic development of the enthalpy and the heat conduction as an input variable is taken into account.

The WO 01/91943 A1 discloses a method in which by means of a simulation and calculation model, the amount of coolant to be applied is calculated in order to obtain the target structure defined desired structure of the casting strand produced during continuous casting. The continuous casting is carried out under on-line calculation on the basis of a simulation and calculation model describing the desired structure of the casting strand, whereby the variable of the continuous casting process affecting the structure formation, such as the specific coolant quantity provided for cooling the strand, is dynamically online, ie during of running casting. With this method it is possible to carry out a continuous steel casting in such a way that desired ferrite and pearlite structures are set and / or eliminated and unwanted precipitates, such as, for example, aluminum nitride precipitates, are avoided at the grain boundaries. The simulation and calculation model includes a metallurgical computational model considering the phase transformation kinetics and nucleation kinetics and a thermal computational model that allows temperature analysis due to the solution of heat equation equations. The basis is in particular the appropriate consideration of the Gibbs energy and the multicomponent systems are integrated into the calculation model. This known simulation and computational model also includes the measure to calculate the proportion of converted material on the basis of the ZTU graphs stored in the computer and the temperature which changes as a function of time, thus also taking into account the optionally non-uniform cooling of the cast strand produced to be able to.

für jede Strangposition dynamisch für die aktuellen Gießverhältnisse in der Gießanlage numerisch zu lösen. Insbesondere bei Dick- und Dünnbrammen sowie Knüppel, Rund- und Vorblockanlagen findet dieses Modell Anwendung. Mit einem integrierten Materialmodell können dann Werkstoffdaten wie Phasengrenzen, Enthalpien, Liquid Fraction Anteile, Dichte und Wärmeleitzahl für jede Analyse und jede Temperatur berechnet werden. Die Temperaturberechnung erfolgt unter Berücksichtigung aller Anlagenkomponenten wie:

• Kokille (Wassermenge, Wassertemperatur, Wassertemperaturerhöhung, Kupferwanddicke, Gießpulvereinfluss)
• Rollen (Durchmesser, Anpresskraft, Rollentemperatur)
• Rührer (Position und Intensität)
• Isolierungen (Verminderung der Wärmestrahlung)
• Sekundärkühlzone (Einzelposition jeder Düse, Wasser- und Luftmenge, Wasser und Luftdruck, Schwallwasser, Wassertemperatur, Leidenfrosteffekte)
• Lagerlücken (kein Rollenkontakt, eventuell mehr Schwallwasser) Rollgängen (Wärmeverlust durch Strahlung und Konvektion an Luft)

With known temperature calculation methods, such as the DSC (Dynamic Solidification Control) method and the DSC (Dynamic Solidification Control) calculation and control program, respectively, which designates a program developed by the applicant, it is possible to use the heat equation $${\mathit{pc\; of}}_p\frac{\partial T}{\partial t}-\frac{\partial }{\partial s}\left(\lambda \frac{\partial T}{\partial s}\right)=Q$$

to solve numerically for each strand position dynamically for the current casting conditions in the casting plant. This model is used, in particular, for thick and thin slabs as well as billets, round and bloc systems. With an integrated material model, material data such as phase boundaries, enthalpies, liquid fraction fractions, density and thermal conductivity can then be calculated for each analysis and each temperature. The temperature calculation takes into account all system components such as:

• Mold (amount of water, water temperature, water temperature increase, copper wall thickness, Gießpulvereinfluss)
• Rolls (diameter, contact force, roll temperature)
• Stirrer (position and intensity)
• Insulations (reduction of heat radiation)
• Secondary cooling zone (individual position of each nozzle, amount of water and air, water and air pressure, splash water, water temperature, Leidenfrosteffekte)
• Bearing gaps (no roller contact, possibly more splash water) roller tables (heat loss through radiation and convection in air)

From the calculated temperature at each strand position further technological parameters can be derived:

Strand shell thickness:

Since the temperature is known at each calculation node, the thickness of the strand shell can be calculated by knowing the solidus temperature from the material model at each time point and for each plant position.

Of particular interest is the average temperature of the strand shell, because temperature fluctuations in the already solidified material can lead to tensions and cracks.

Location of the marsh tip:

As soon as all temperatures of the strand cross-section are smaller than the solidus temperature, the strand is solidified. The position of complete solidification is of particular importance in a casting plant, since it must not exceed the last roll in order to prevent an uncontrolled swelling of the strand (whale formation). For performing a so-called soft reduction, the exact position of the sump tip is also required.

Solid Fraction Shares (Solid Phase Shares):

In addition to the shell thickness, the isolines for all Solid Fraction fractions in the solidification interval and the isolines below the solidus temperature (Ts-10 ° C to Ts-50 ° C) can also be calculated. With this method, it is also possible to evaluate the formation of internal cracks in the cast strand in the plant and the relationship between internal cracks near the zero toughness temperature T _NZ (ZDT) to clarify. Characteristics of the internal crack susceptibility are the Zero Strength Temperature (ZST) or, better, the Zero-Toughness Temperature (ZDT). With the temperature T _NZ (ZDT) solid fractions of 0.97, 0.98, 0.99 and 1.0 are equated in the literature. The starting point is a crack formation in the range 0.90 <fs <1.0. The crack propagation extends outwardly into the region of zero toughness into the temperature range Ts-10 ° C to Ts-50 ° C. The Solid Fraction Shares are also needed to determine the soft reduction positions. The optimum time for soft reduction is determined by the liquid fraction ratio (solid fraction fraction) in the strand core, which is a criterion for evaluating the effect of soft reduction on center segregation. During the solidification of the liquid steel, the different solubility of the alloying elements in solid and liquid causes an enrichment of the alloying elements in the molten phase. As a result, the last solidifying areas have a higher concentration than the initial concentration (nominal analysis). In this area, this leads to a lowering of the solidus temperature. This is not important for whale formation, but for the detection of hot cracks.

ductility:

For a given ductility curve of a material and a value for the minimum permissible ductility in the crack-critical bending and straightening range, the ductility profile over the entire surface can be represented. Likewise, isotherms of the critical ductility profile can be used for the localization of internal cracks.

bulging:

With the aid of the temperature and the strand shell thickness, the bulge and the associated expansion can be calculated at each plant position, taking into account the roll distances. The elongation can be compared with a given maximum allowable elongation.

Voids and nuclear blockers:

One of the metallurgical problems of continuous casting is the formation of a large directional dendritic zone at the expense of the area of the globulitic core zone, since the significantly higher cooling rates in continuous casting cause large temperature gradients at the mushy zone interface.

During solidification a volume shrinkage occurs. These resulting cavities must be filled with melt. If a continuous flow with liquid melt can no longer or insufficiently be ensured, core cavities (billets and billets) and nuclear pores / core loosening (slabs and billets) may form during solidification.

In slabs, the sump tips wedge-shaped due to the one-dimensional heat dissipation and solidification. Local crystal bridges do not lead to a complete constriction of the sump, so that the make-up of melt is still possible and no Kernlunker but at most loosening occur.

Round and square strands have a tapered conical crater due to the two-dimensional heat dissipation and solidification, is fed by the liquid metal to compensate for the solidification shrinkage. Favorably oriented, leading dendrites can form bridges, complete the sump underneath and obstruct or prevent desserts with melt from above. These processes lead in the strand to Kernlunker and core loosening.

Prerequisite for the calculation of voids and pore formation is the temporal temperature field of the strand. By means of the temperature distribution and the rate of solidification calculated therefrom, the secondary dendrite arm spacing (SDAS) and a permeability which counteracts the hydrostatic pressure can be calculated. The permeability describes the permeability of the Dendrite. The greater the permeability, the greater the permeability. The pressure loss of the inflowing melt increases with decreasing permeability. The make-up ends when the pressure loss of the feeding flow is greater than the ferrostatic load. This is the case with a plot of pressure loss and hydrostatic pressure in bar over the distance from the pouring mirror in meters (m), and thus over the cast strand length, intersection of the curves of pressure loss and hydrostatic pressure of the case.

Solidification structure (macrostructure):

The center segregations are associated with the appearance of the trans-crystalline (directional) digestion structure. The causes are flows of the residual melt in the area of the sump tip, which lead to a redistribution of the alloying elements. The enriched melt reaches the center of the strand and causes the positive center segregation there. It is characteristic of a mid-segregation that the enrichment in the middle of the strand always involves a depletion of the adjoining areas. The positive segregation must correspond quantitatively to the negative one. It is of great importance to see how the proportion of globulitic (undirected & equiaxed) solidification structure depends on continuous casting techniques and steel composition. If the solidification structure is globulitic (undirected & equiaxed), the observed segregations are usually smaller.

High carbon steels have a much greater tendency for center segregation (macrosegregation) than those with low or medium carbon content. High carbon content favors the transcrystalline (directional) solidification and thus the center segregation. The material is additionally weakened by internal defects, which leads to fragility during transport.

In order to avoid surface defects (tensile roughness) in the finished rolled cold strip in the case of ferritic steels, it is desirable to achieve a minimum proportion of globulitic (equiaxed) microstructure.

From the calculated temperature fields, the solidification rates and the temperature gradient at the solidification front can be determined. With a coupled material model CET, the proportion of globulitic structure can then be calculated. The globulitic part of the solidification structure can be increased by using stirrers and casting with a low overheating temperature.

Microstructure: ▪ γ / α phase transformation

An important aspect of the ductility characteristics of slabs is the structural condition. In the "hard cooling" the strand is e.g. To avoid bulges strongly cooled to quickly get a thick strand shell. In this case, the temperature may fall below the transformation temperature γ / α. Since ferrite is much softer than austenite, it is believed that the deformation of the material is preferably at the ferrite spaces. The break is then initiated at the ferrite spaces. From calculated temperature fields, the cooling rates can be calculated for any line positions. With these cooling rates and the minimum temperatures achieved, the microstructure distribution can be read off with a coupled synthetic ZTU model.

▪ Elimination

In most studies, ferrite embrittlement under A ₃ temperature is explained by the interaction of ferrite spaces and precipitates. The ferrite spaces form when the A ₃ temperature falls below the austenite grain boundaries and precipitates of the nitrides and carbonitrides take place in these ferrite spaces.

Scale calculation:

In a "hot driving" no splash water is applied in parts of the horizontal region of the cast strand. As a result, the forming scale does not break off and the heat dissipation of the strand is reduced by a scale layer. By adding the existing and the chipped scale, the loss of production can be determined.

From practice, the following control systems are known: Spray plan:

Using tables, the water quantities for each casting speed control point are specified for each control loop. Between these interpolation points, the quantities of water are linearly interpolated. If the casting speed is changed, the water quantities in all control loops are changed immediately.

LifeTime regulation:

If the casting speed is changed, the water quantities of all control loops are not changed immediately. The changes are determined by the strand age.

Temperature control:

For certain positions in the secondary cooling, usually the end of a cooling zone, setpoint temperatures are specified depending on the material group. The spray water volumes are now controlled so that these predetermined temperatures are set. As a result, the strand retains the same temperature distribution and thus constant qualities even with changes in the casting speed. By dynamically changing the setpoint temperature curve, you can automatically react to unwanted problems.

Thus, by lowering the setpoint temperatures early the formation of a too long sump tip can be avoided.

Swamp tip control:

Control of the amounts of water or the casting speed to the sump tip to a desired position.

Gießgeschwindigkeitsregelung:

The casting speed is varied to set the sump tip at a predetermined position or to reach a desired temperature.

Duktilitätsregelung:

The temperature profile is controlled so that the surface temperatures in the crack-critical bending and straightening range do not fall below a critical value. This critical temperature value is calculated from the intersection of the given ductility curve with the value of a critical limit (e.g., 75%).

Strain control:

Just as the current strain can be calculated from the current temperature curve, a maximum permissible temperature value can also be calculated back from the permissible maximum strain. The calculation of the maximum permissible temperature values takes place from the maximum elongation with the aid of a recursive calculation method, since with decreasing temperature the strand shell becomes thicker and the bulge and thus also the expansion decreases.

The invention has for its object to provide a solution with which the influence of cooling on the production of a cast strand obtained in continuous casting can be further improved.

In a method of the input specified type, this object is achieved by claim 1.

Various control mechanisms can now be implemented with the method according to the invention, all of which bring about an improvement in the cooling of the casting strand forming during continuous casting and / or its geometric, mechanical, microstructural or surface properties or configurations. The basis is always at least one simulation and calculation model, to which the current temperature distribution over the cast strand length and / or in each considered cross-section of the cast strand can be calculated. With the help of such one or more such simulation and computational models, various control concepts with respect to the macrostructure, the microstructure, to achieve a uniformly formed sump tip, to regulate a constant outlet thickness of the cast strand and to reduce voids and Kernlockerstellen can be realized, which are still outlined below ,

Control concept macrostructure:

For a control concept directed to the macrostructure, it is advantageous if, according to the invention, a desired macrostructure, which is the solidification structure, has a globulitic structure fraction of at least 30%, preferably at least 35%, and in the case of ferritic steel at least 40 %, preferably at least 45%. The% data refers in each case to the surface of a micrograph.

It is advantageous for the adjustment of the macrostructure, but also of the microstructure, further, if the casting speed and the amount of spray water are controlled to set the desired macrostructure in a continuous casting machine equipped with a stirrer and in addition to that in a continuous casting machine with adjustable stirrer the desired macrostructure and / or the desired structure composition of the casting strand optimal stirrer position and the stirring intensity can be calculated and adjusted by means of or based on the simulation and calculation model, which further distinguishes the invention. At a given overheating, the casting speed and / or the secondary cooling is controlled so that the desired structure is achieved.

Control concept microstructure:

A control concept for the formation of the microstructure in the forming cast strand is characterized in that for setting the desired microstructure, the simulation and calculation model ZTU (time-temperature conversion) diagrams includes and calculated using an online temperature model of the cast strand Gießstrangabkühlraten be combined such that for each defined calculation element of each Gießstrangquerschnitts the current Gießstrangkkühlrate and the resulting structure composition can be calculated and calculated and by controlling the Gießstrangabkühlraten the desired structure is set.

With the aid of this embodiment of the method according to the invention, it is possible to adjust the cooling conditions on the forming cast strand during continuous casting such that the microstructure transformation takes place uniformly over the cross section and in particular in the edge regions to the surface side of the cast strand and ferrite spaces with a ferrite content of about 5 40% and thus in areas with low ferrite levels on the grain boundaries can be avoided.

A continuous, dynamic and constant online calculation of the respectively on a Gießstrangquerschnitt adjusting microstructure, i. the microstructure composition and microstructure distribution which arises in such a cross-sectional area has hitherto not been carried out in the continuous casting process in the production of a metal strand, in particular a steel strand.

With the embodiment of the method according to the invention, it is now possible to uniformly cool a casting strand during its manufacture, since for each casting strand cross-section the respective cast strand cooling rate and the structure arising at any time in this casting strand cross-section, i. the particular microstructure composition, can be calculated. If irregularities or undesired microstructural compositions show up, it is possible with the aid of the simulation and computational models to carry out such readjustment and modification of the respective cast strand cooling rates that a uniform cooling and thus a nearly uniform microstructure on the surface of the respective cross section is achieved.

With the method according to the invention and its refinements and further developments, and in particular with the simulation model or mathematical models stored in a corresponding computer unit, it is possible to that the limits of the third ductility minimum occurring at different cooling rates for the respective steel grades are calculated and plotted. Such a possibility is in the DE 10 2012 224 502 A1 described and can in principle also be adapted for use in casting a casting strand in a continuous casting. The respectively calculated cooling rates can be plotted in the respectively calculated ZTU diagram (s) or in ZTU diagrams calculated on the basis of measured values and stored in the simulation and calculation model and used for the calculation of the then resulting structure fractions. In each of the created ZTU diagrams, the ductility minima occurring at the different temperatures for the respective steel grade can also be drawn. An online temperature model, with which the respective cooling rates are calculated, represents the Dynamic Solidification Control (DSC) method or model. With the help of the thus constructed simulation and calculation model can at any position in the casting direction of the casting strand a Gießstrangquerschnitt with then be created there existing microstructure distribution and visualized or presented. For all calculation elements across the cross-section of the cast strand at a defined, specific location, the respective current cooling rates and the resulting microstructural fractions can be calculated.

With the method according to the invention and its refinements and developments, the amount of coolant to be applied to the respective surface side (s) of the cast strand, in particular the amount of water, or the position of the nozzles, for example by adjusting the height of the nozzles, can be regulated and controlled in such a way that a uniform transformation of the microstructure can be obtained from the austenite in the ferrite on the narrow and / or broadside. As a result, the risk of surface cracks occurring as a result of uneven cooling can be reduced, in particular in the case of strong, intensive cooling.

The aim of an embodiment of the method according to the invention is to achieve a uniform desired microstructure distribution. In an embodiment, the invention is characterized in that the Gießstrangabkühlraten at their respective position with respect to the casting strand by controlling the impacting in this area each on the casting strand coolant quantity and / or the control of the location or the surface of the impact of the coolant on the cast strand in such a way be controlled and regulated that the most uniform transformation of the metal structure on the narrow side and / or the broad side of the cast strand, in particular in a steel strand while avoiding the formation of the deposition of ferrite grains austenite grain boundaries, so-called Ferrites, is achieved.

According to the invention, it is then also possible in this case to calculate ZTU diagrams or diagrams directly by means of the simulation and computational models that are used and to base the control of the coolant admission. The invention therefore further provides that the ZTU (time-temperature conversion) diagrams are calculated by means of the simulation and calculation model. For this purpose, a recursive calculation method is necessary, with the aid of which the required cooling intensity of the secondary cooling is calculated from the cooling rate.

It is possible that the Gießstrangabkühlraten at their respective position with respect to the Gießstrangs by controlling the impacted in this area respectively on the Gießstrang coolant quantity and / or the control of the location or the surface of the impact of the coolant on the Gießstrang be controlled and controlled so that the most uniform possible transformation of the metal structure over the respectively considered cross-sectional area or side surface of the cast strand is achieved.

In particular, the application of the method according to the invention for the control of a uniform microstructure formation and a uniform Cooling of the narrow sides of a cast strand, which is generally rectangular in cross-section, to avoid cracking is advantageous. The invention therefore also provides that the Gießstrangabkühlraten be determined with respect to the narrow sides of the casting strand and the incident on the narrow sides of the casting strand coolant quantity and / or the location or area to which (n) the coolant on the respective narrow side of the casting strand is applied, is controlled in dependence of the adjoining in the boundary region to the surface of the narrow side structure and / will be.

Control concept uniform sump tip

A control concept for achieving a uniformly shaped sump tip can be realized according to another embodiment of the invention in an advantageous manner that for setting the desired position and / or formation of the sump tip of Gießstrangs or on the basis of or simulation and computational models a desired sump length in The SPDF (Solidification Point Difference Factor) value (see definition below) is calculated and, if a maximum SPDF _max value is exceeded, the desired SPDF value is adjusted and adjusted by increasing the amount of sprayed water in the edge zones of the casting strand in the area of the sump tip ,

Control concept constant outlet thickness

A control concept for achieving a constant outlet thickness of the cast strand can advantageously be realized according to the invention by adjusting the desired geometric dimension of the cast strand by means of or on the basis of the simulation and calculation models starting from the desired final thickness of the cast strand at the end of the plant to the mold over the length of the casting strand which calculates, adjusts and adjusts a position for providing the cooling rate and / or deformation necessary for achieving the desired dimension of the casting strand for each segment and / or roll. In this embodiment of the invention, it is also expedient if the segment adjustment and / or roller adjustment to be set at each segment there to achieve a strand thickness necessary for achieving the desired final thickness (temperature-dependent) density (determined from the respectively determined temperature or temperature distribution) ( of the material) and the density difference resulting over the casting length is calculated by means of or on the basis of the simulation and calculation models, which the invention also provides.

Control concept voids formation

To reduce voids and nucleation sites, resorting to cruise control is particularly advantageous. In order to realize a control concept based thereon, the invention is characterized in a further embodiment in that for setting the desired surface finish or internal structure of the cast strand and for reducing voids or Kernlockerstellen means or on the basis of or simulation and calculation models on the cast strand length a desired cavity diameter is calculated and when a predetermined maximum value of the cavity diameter is exceeded, the casting speed is reduced.

In particular, the method according to the invention is used in the secondary cooling of the cast strand, which finally also provides the invention in an embodiment.

Fig. 1

in schematischer Darstellung eine Stranggießanlage mit Gießstrang,

Fig. 2

ein mit einem erfindungsgemäßen Simulations- und Rechenmodell berechnetes ZTU-Diagramm mit eingezeichneten Gießstrangabkühlkurven,

Fig. 3

in schematischer Darstellung einen Querschnitt durch den Gießstrang mit Darstellung der bei einer Abkühlung gemäß Fig. 2 entstehenden Gefügeanteile,

Fig. 4

eine der Fig. 2 entsprechende Darstellung bei ungleichmäßiger Abkühlung des Gießstranges nach dem Stand der Technik,

Fig. 5

das ZTU-Diagramm nach der Fig. 4 mit eingezeichnetem kritischen Ferrit-Bereich,

Fig. 6

in schematischer Darstellung den Regelungsmechanismus zur Erzielung einer gleichmäßigen Kühlung, insbesondere der Schmalseiten des Gießstrangs,

Fig. 7

ein Regelungsschema für die Realisierung eines Regelungskonzeptes zur Einstellung eins gewünschten Makrogefüges,

Fig. 8

ein Regelungsschema für die Realisierung eines Regelungskonzeptes zur Erzielung einer gleichmäßig ausgebildeten Sumpfspitze,

Fig. 9

ein Regelungsschema für ein Regelungskonzept zur Erzielung einer konstanten Auslaufdicke des Gießstrangs und in

Fig.10

ein Regelungsschema eines Regelungskonzepts zur Verminderung von Lunker- und Kernlockerstellen im Gießstrang.

The invention is explained in more detail below by way of example with reference to a drawing. This shows in

Fig. 1

a schematic representation of a continuous casting plant with cast strand,

Fig. 2

a ZTU diagram calculated with a simulation and calculation model according to the invention with drawn cast strand cooling curves,

Fig. 3

in a schematic representation of a cross section through the cast strand with the representation of a cooling according to Fig. 2 resulting microstructural components,

Fig. 4

one of the Fig. 2 corresponding representation with uneven cooling of the casting strand according to the prior art,

Fig. 5

the ZTU diagram after the Fig. 4 with marked critical ferrite area,

Fig. 6

a schematic representation of the control mechanism to achieve a uniform cooling, in particular the narrow sides of the casting strand,

Fig. 7

a control scheme for the realization of a control concept for setting a desired macrostructure,

Fig. 8

a control scheme for the realization of a control concept to achieve a uniformly shaped sump tip,

Fig. 9

a control scheme for a control concept to achieve a constant outlet thickness of the casting strand and in

Figure 10

a control scheme of a control concept to reduce voids and Kernlockerstellen in Gießstrang.

The Fig. 1 shows the generally designated 1 Gießbogen a continuous casting, starting from a continuous casting mold 2, in which a liquid molten steel is poured 3, extends over the bending region 4 and the straightening region 5 into the region of solidified Gießstranges 6. In the course of the pouring arc of the forming cast strand 6 is guided on hydraulically adjustable support rollers 7 and cooled with spray water 8 as a coolant that is sprayed from the outside on its surface sides, so that within the cast strand 6, a liquid core 9 of non-solidified melt. 3 forms until this liquid core ends after passing through the straightening region 5 in the form of a sump tip 10 in the cast strand. The spray 8 emerges from spray nozzles, which are arranged to several in each one engagable segment 29, of which a plurality of strung together along the casting strand 6 is arranged. In this area, the casting strand 6 is also exposed to a water cooling 11. The cast strand 6 has a substantially and approximately rectangular cross-sectional area with two opposite broad sides and two opposite narrow sides. During the cooling of the molten steel 3, different microstructures and microstructures form within the cast strand 6 and thus in each (conceivable) cross-sectional area over those of the continuous casting mold 2 to the sump tip 10 or thereafter, depending on the respective steel grade and respectively set cast strand cooling rates formed continuous solidified casting strand 6 extending length of the casting strand 6 or metal strand, in particular steel strand, from.

The Fig. 2 shows a ZTU diagram drawn in the context of carrying out the control concept according to the invention for setting a desired microstructure with the simulation and computational model used here with cast strand cooling curves 12-15, which are characterized by their positions 12 'on the surface of a broad side of the cast strand 6, 13 'in the transition region of the broad side to an adjacent narrow side of the Gießstranges 6 and 14 'and 15' on the narrow side of the casting strand 6 differ, as shown schematically in the upper right partial image, which is a cross section through a portion of a casting strand 6, schematically. The individual Gießstrangabkühlkurven 12-15 are each different Gießstrangkkühlraten associated with the result that shown at the respective positions 12'-15 'in the simulation and calculation model respectively associated and detected calculation element 16 (shown the position 14' associated computing element 16 ) of the cross-sectional area set different structural components. In FIG. 2 are the Gießstrangabkühlraten and the structural components on a cross section after 2235 mm, so even before the bending area shown. The different Gießstrangkkühlraten and obtained microstructural components are in the upper left part of the Fig. 2 in the respective columns 12 "to 15", which are respectively associated with the same number cast strand cooling curve and the same-numbered position. The Gießstrangabkühlkurve 12 is thus carried out with a Gießstrangkkühlrate of 0.1 K / s and there is a microstructure of 100% austenite in the area 12 'adjacent area. By means of the cast strand cooling curve 13, with a cast strand cooling rate of 2.30 K / s in a region adjoining the edge of the cast strand 6, a composition of the structure consisting of 77.91% ferrite, 1.65% pearlite, 4.24% bainite and 16.2% austenite. The Gießstrangabkühlkurve 14 is performed with a Gießstrangkkühlrate of 9.93 K / s and in the adjacent to the position 14 'region 16 is a microstructure composed of 72.73% ferrite, 3.13% perlite, 7.17% bainite and 16.97% austenite. The Gießstrangabkühlkurve 15 is performed with a Gießstrangkkühlrate of 5.30 K / s, so that in the adjoining the position 15 'cross-sectional area of the casting 6, a microstructure composition is composed of 10.41% ferrite and 89.59% austenite.

In the above with reference to the Fig. 2 example explained, the cooling rates are determined, for example by means of Dynamic Solidification Control (DSC) and calculated and in the either using the simulation and calculation model calculated ZTU diagram or in such a computing unit 17, see FIG. 6 and associated description, stored and deposited ZTU diagram drawn. The simulation and calculation model can also be used to calculate the structural components then obtained in the individual calculation element 16, so that the cast strand cooling rates can be controlled and influenced in a targeted manner for setting the desired structure composition at the respective position, for example by regulating the amount of coolant sprayed at the respective position or by influencing the spray area and thus the surface on which the coolant impinges on the respective surface side of the casting strand 6.

With the above based on the Fig. 2 explained example of an uneven cooling can be adjusted and is now also a uniform cooling of the narrow side 18 of the casting strand 6 set and achieved. In this uniform cooling is at a casting speed of the casting strand 6 of 1.09 m / min in the adjacent to the narrow side 18 cross-sectional area for the same considered cross-sectional area of the casting strand 6 from the Fig. 3 apparent structure composition. While liquid melt 3 is still present in the core 9, a ferrite region adjoining the surface of the casting strand 6 forms on the narrow side 18. At the position of 2.235 m below the casting level, ie even before the bending region, liquid melt 3 is still present in the core 9. In Mushy area 30, the first dendrites form. These solidify in this analysis (MediumCarbon) first to austenite 31. On the narrow side 18 forms due to the lower temperatures on the surface of the casting 6, a ferrite 32 from. The middle of the narrow side 18 is cooled to the strongest, so that there already the first bainite 33 is formed.

In this way, with the method according to the invention, uniform cooling and, as a result, a microstructure composition, in particular in the region of the narrow side 18, can be formed, in which the temperature control is such that the ductility is high enough to avoid cracks in the surface regions. If, on the other hand, the casting strand cooling rates were not controlled and influenced in the manner according to the invention by means of a simulation and calculation model, and if uneven cooling of the narrow side 18 were to occur, then there would be those in the Fig. 4 and 5 shown progressions of Gießstrangabkühlkurven 12a to 15a and at the in the Fig. 2 and 3 analog positions 12a 'to 15a' to the analog to the casting cast strand cooling rates and structural surface portions 12a "to 15a". In the right part of the picture Fig. 4 Due to the given ductility, the formation of cracks in the casting strand 6 would have to be expected. In the Fig. 5 In addition, the critical ferrite region, which extends over the range of 5% to 40% proportion of ferrite in a microstructure cross section, is drawn into the ferrite region 20. The Gießstrangabkühlraten and Gießstrangabkühlkurven can be controlled according to the invention so that this range of ductility minimum in the cooling of the casting strand 6 is not set.

In order to carry out the desired uniform cooling and uniform structure distribution in each considered cross-section of the casting strand 6 at an arbitrary position between the mold 2 and the end of the casting machine of the casting of the continuous casting 1, according to the invention a control and regulation of the application of broadsides 19 and / or the narrow sides 18 of the casting strand 6 are provided. The basic structure of this control and regulation shows the Fig. 6 , The centerpiece is the arithmetic unit 17, in which the simulation and calculation model 21, which is based on a mathematical / physical model, as for example in the DE 10 2012 224 502 A1 is described, is deposited. With the help of this simulation and calculation model 21 and for example by means of the Dynamic Solidification Control (DSC) method at the respective positions 12 'to 15' determined temperatures and Gießstrangabkühlraten or cast strand cooling curves 12 to 15 calculated in this arithmetic unit 17 which adjusts itself to the particular cross-sectional area structure distribution 22, in particular on the narrow side 18, calculated. In a test step 23, it is checked whether the calculated microstructure distribution 22 is a uniform microstructure distribution. If this is the case (test result: OK 24), the process is continued with the current coolant application. If a negative result 25 is ascertained as the result of this test step 23, a change in the coolant flowing out of the respective nozzles, in particular water, and / or the position of the nozzles relative to the surface of a broad side 19 or narrow side is produced with the aid of the simulation and calculation model 21 18 or the distance of the nozzle from the respective associated surface side changed, as indicated in step 26. With the implementation of step 26 is intervened in the spray plan 27 of the respective loop and / or in the nozzle distribution and nozzle assembly 28. The intervention in the spray plan is that the output to the respective surface side of the casting strand 6 coolant quantity is changed, that is increased or decreased. The influence with respect to the nozzle distribution 28 is that thereby the position of one or more nozzles along one or more side surface (s), ie the broad side 19 and / or a narrow side 18, but in particular a narrow side 18, is changed. This can be achieved, for example, by spray nozzles which are height-adjustable in relation to the height (thickness) of a cast strand 6, so that an adjustable relative position of the respective nozzle to the narrow side 18 can be adjusted by this height adjustability. However, it is also possible or supplementary possible, the distance of the respective nozzle of a broad side 19 or narrow side 18 formed changeable, so that on such an adjustment of each nozzle sprayed surface of a broad side 19 or narrow side 18 can be influenced. Part of the control step 28 is thus also a control and regulation of the nozzle distribution with wide control circuits. Which From the adjustment in steps 27 and 28 resulting changes in the amounts of coolant and the coolant, which each bring changed Gießstrangkkühlraten with it, then in turn flow into the simulation and calculation model 21, so that there is a closed loop. By means of this control loop, the structure formation on the broad sides 19 and the narrow sides 18 of a cast strand 6 can be controlled and influenced in a targeted manner, the influencing of the structure formation and structure distribution on the narrow sides 18 of the cast strand 6 being provided according to the invention. It is aimed at a uniform cooling.

By means of the arithmetic unit 17 and the simulation and calculation model 21, values are continuously and continuously calculated during the production of the cast strand 6 which describe the formation of the respective microstructure composition and control process parameters, ie in particular the coolant admission, so that on the basis of these calculated values and process parameters a dynamic online control of the production of the casting strand 6 and in particular the cooling of the casting strand 6 is possible and adjusted. In this case, the simulation and calculation model 21 combines ZTU diagrams and cast strand cooling rates determined by an online temperature model such that for each defined calculation element 16 of each Gießstrangquerschnittes each Gießstrangabkühlrate determined at a respectively defined and determined position and the resulting microstructure composition is calculated and is influenced by the control of Gießstrangabkühlraten to the effect that adjusts the particular desired structure or desired structure composition in the respective calculation element 16. In particular, this regulation and control is performed on the narrow sides 18 of the cast strand 6. The control concept thus has an effect on the height-adjustable side cooling of the cast strand 6 and the control of the narrow side injection water quantity on the basis of the microstructure calculation.

Control concept for setting a macrostructure (CET "Columnar to equiaxed transition").

To avoid surface defects, the proportion of globulitic structure in ferritic steels should be above 45%. For other materials, to improve the internal quality of a cast strand, it is also desirable to obtain a globulitic fraction of at least 35%. The globulitic part of the structure is dependent not only on the overheating, the casting speed and the secondary cooling, but above all on the type and position of the stirrer used in the casting of a molten metal, in particular molten steel in continuous casting. With a non-adjustable stirrer and a predetermined overheating, the casting speed and the spray water quantities (coolant) can be controlled so that the desired solidification structure is achieved with model calculations. Adjustable stirrers also allow their optimal position and intensity to be calculated and adjusted. The control concept for setting a macrostructure (CET) is the Fig. 7 refer to. As usual, current process parameters are determined and fed to the mathematical-physical model, which is part of a simulation and calculation model 21. With the aid of this simulation and calculation model 21, the globulitic fraction of the macrostructure in the macrostructure which is established over the cast strand length at a respectively defined location is calculated in% and it is checked whether this calculated globulitic fraction is ≥ the desired globulitic fraction. If so, the process parameters remain unchanged. If not, the stirrer action is increased, if possible, and / or superheat is reduced and / or the casting speed is increased. The calculation model 21 is checked using micrographs. If the micrographs show a different globulitic component of the macrostructure than results from the calculation, the calculation model is adapted accordingly. With this control concept, in particular the power-adjustable stirrer with associated automation and the secondary cooling are applied and influenced.

Control concept for achieving a uniformly shaped sump tip

If a uniform amount of spray water is applied over the width of the cast strand 6, a uniform temperature distribution across the width of the cast strand is also established. Only at the edges, i. the transitions to the adjacent vertical side areas, the temperature drops much more due to a two-dimensional heat dissipation. This "two-dimensionality" refers to the fact that the mutually perpendicular sides are both supplied with cooling water or coolant. The narrow sides are usually acted upon only in the upper part of the strand guide below the mold with cooling water. In the lower part of the strand guide, on the other hand, mainly the heat radiation on the narrow sides in two dimensions leads to the temperature drop at the edge.

The result of uniform cooling is a uniformly formed sump tip. In order to reduce the strong temperature drop at the edges, the applied or applied spray water volumes over the strand width are often not constant, but the marginal areas then so-called edge control loops are assigned by means of which a smaller specific amount of water than in the remaining area of the surface of the strand width is applied , This increases the surface temperature of the edge and the temperature drop at the edge is then not so high. Negative here, however, is that the strand over its width no longer solidifies uniformly, but the sump tip forms a so-called "W" shape. An uneven sump tip is very problematic. It can lead to an increased center segregation at the edges and thus in itself set an increased internal defect at various points of the casting strand 6. Furthermore, no optimal position for performing a soft reduction can be determined. This problem is in the control concept according to the invention to achieve a uniformly shaped bottom tip by avoiding defining and forming a so-called "SPDF" ( S olidification Point Difference Factor) value that describes deviations of the swamp length. This SPDF value is: $$\mathrm{SPDF}=\frac{\mathit{maximum}\mathit{marsh\; length}-\mathit{marsh\; length}\mathit{in}\mathit{the}\mathit{strand\; center}}{\mathit{marsh\; length}\mathit{in}\mathit{the}\mathit{strand\; center}}$$

The quantities of water in the peripheral zones are now regulated so that the SPDF value does not exceed a predetermined level, the SPDF _max value. If this is the case, the spray water volumes in the edge zones are increased again. The determination of the respective solidification position takes place with the aid of a mathematical-physical model which forms or is part of the one or more possibly simulation and calculation models 21. The regulatory scheme is the Fig. 8 refer to. With the aid of the simulation and calculation model 21, the solidification front is calculated and determined. Furthermore, it is checked whether the currently calculated SPDF value ≦ a desired, maximum SPDF _max value. If deviations from the SPDF _max value can be detected here, the temperature difference in the edge areas of the casting strand 6 is reduced by adjusting the specific water quantities between the center and edge control loops. This control concept acts and applies the secondary cooling and the measurement and feedback of possible measured values into the simulation and calculation model 21.

Control concept for achieving a constant outlet thickness of the cast strand

In order to always have the same starting conditions in a rolling mill following the continuous casting plant with respect to the cast strand 6 to be rolled, it is desirable to produce a cast strand or slabs made therefrom with a constant final thickness. For all steel grades, casting speeds and the resulting temperature distribution in the Gießstrang 6 the slabs produced at room temperature must then not exceed or fall below a certain thickness tolerance. From a material model integrated into the simulation and calculation model 21, for example when using the so-called Dynamic Solidification Control (DSC) model, the density of the casting strand 6 that then arises can be determined for each analysis and each temperature. Important here is the knowledge of the transformation temperatures, ie at which temperature the material undergoes a phase transformation. The Kokillenaustrittsmaß can not be determined directly from the desired final thickness and the density difference. Namely, the individual segments 29 and rollers have to be adjusted in such a way that they push away the natural sock formed by the density difference. For this purpose, the temperature difference in each calculation element 16 and the associated contraction must be calculated for the current process values. The contraction of the still liquid material (metal, steel) does not have to be taken into account, as it constantly flows through the ferrostatic load inside the strand. Thereafter, starting from the required final thickness from the end of the system to the mold down over the length of the casting strand 6, the employment for each segment 29 and its rollers 7 is calculated. If the process values are changed, a new determination of the segment position takes place immediately. If the slabs are to have a thickness of 250 mm, for example, when cold at 25 ° C., the difference in density and the temperature distribution at the last setting position, ie at the last segment 29 of the cast strand 6 before separation of a slab, may be required there Thickness can be calculated. The hydraulically adjustable segments in slab casters or adjustable single rolls in long-tailed plants serve as a strand setting. Likewise, with knowledge of the difference of the temperature distributions over the cross section and / or the length of the cast strand 6 between the penultimate and last setting position of the cast strand 6 and the resulting volume shrinkage, the local employment can be calculated again. The Gießstrangdicke at the exit from the mold 2, however, is determined plant-specific and fixed and can not dynamic be adjusted. In order to still obtain the desired final thickness in case of temperature fluctuations due to stationary process conditions such as a changed overheating, it is necessary to set the Kokillenaustrittsmaß of the cast strand 6 slightly larger than it would have to compensate for the natural shrinkage. About an Anstellverteilung this additional thickness decrease is distributed over the individual Anstellpositionen. If the calculated material thickness after cooling is already less than the specified final thickness even without setting, this can not be compensated by changing the casting speed or amount of spray water. These changes would only delay the end of the cooling period. To reduce the shrinkage, the outlet temperature of the strand on the mold 2 then has to be reduced by, for example, a reduction in the mold temperature. But this should not be automated without a warning to the operators. A control scheme implementing this control concept for achieving a constant outlet thickness of the cast strand 6 is disclosed in US Pat FIG. 9 shown. Influenced and acted upon with this control concept, the hydraulic segment and / or role employment.

Control concept for the reduction of voids and core-lock points in the cast strand

For the calculation of voids and pore formation in a cast strand 6 during continuous casting, the knowledge of the temporal temperature field of the cast strand 6 is a prerequisite. By means of the temperature distribution and the rate of solidification calculated from this, the secondary dendrite arm spacing (SDAS) and a permeability which counteracts the hydrostatic pressure can be calculated. The permeability describes the permeability of the dendrite structure. The greater the permeability, the greater the permeability. The pressure loss of the inflowing melt increases with decreasing permeability. The make-up ends when the pressure loss of the feeding flow is greater than the ferrostatic load. In the application of the pressure loss and the hydrostatic pressure in the unit of measure "bar" over the cast strand length or the distance of the viewing place from the pouring mirror in the unit "m" the limit is reached exactly at the intersection of pressure loss and hydrostatic pressure. From the literature it is known that the voids volume is a function of the casting speed and with an increase in the casting speed, the voids volume increases almost linearly. The control concept according to the invention consists in varying the casting speed in a continuous casting plant for slabs and long products (billet, billet or round plants) such that the shrinkage diameter determined with the mathematical-physical calculation model or one of the simulation and calculation models 21 is a given Measured value does not exceed. As a result, although the productivity of the system can be reduced, but in any case this improves the quality of the cast strand 6 obtained. The regulatory scheme for this regulatory concept is in the FIG. 10 shown. It can be seen that with the aid of the simulation and calculation model 21 the voids diameter (at the respective location of the cast strand 6) is calculated and compared with the desired size, ie a desired voucher diameter. If the calculated blow hole diameter is greater than specified, the casting speed will be lowered to reduce the blowhole diameter that will be created.

With this control concept, the hydraulic segment and / or roller adjustment as well as the measuring and control systems of the continuous caster are influenced and acted upon

LIST OF REFERENCE NUMBERS

1

casting bow

2

ended mold

3

Molten steel / melt

4

bending area

5

leveling range

6

cast strand

7

role

8th

Coolant / splash water

9

liquid core

10

crater tip

11

Coolant / water cooling

12 - 15

Gießstrangabkühlkurven

16

computing element

17

computer unit

18

narrow side

19

broadside

20

ferritic

21

Simulation and calculation models

22

structure distribution

23

Test step

24

positive test result

25

negative test result

26

step

27

spraying plan

28

nozzle distribution

29

segment

30

Mushy - structure

31

Austenite structure

32

ferrite structure

33

Bainitic structure

Claims (12)

1. Method of producing a metal strip, particularly a steel strip, in the casting curve (1) of a continuous casting plant, comprising pouring a metal melt, particularly steel melt (3), in a continuous casting procedure to form a cast strip (6), which is cooled by coolant (8, 11) and if desired reduced in thickness, wherein on the basis of one or more simulation and computation models (21), for example the DSC (Dyanmic Solidification Control) computation and control program, which describe or calculate the time-dependent temperature distribution over the cast strip length and the formation of a desired structure of the cast strip (6) over the cast strip length and which are filed in a computer unit, there is, during production of the cast strip (6), constant and continuous computation on-line by means of a computer unit (17) and the simulation and computation model or models (21) of values which describe the formation of the respective structural composition and control this or process parameters influencing the cast strip information and on the basis of which the cooling of the cast strip (6) and/or the casting speed is or are dynamically set on-line during production of the cast strip (6),
   characterised in that
   the simulation and computation model or models (21) filed in the computer unit realises or realise on the basis of mathematical/physical models, which are a constituent of the simulation and/or computation model or models (21), different regulation concepts with respect to the macro-structure, the micro-structure, for achieving a uniformly formed end of liquid phase, for regulation of a constant exit thickness of the cast strip and for avoidance of voids and unconsolidated core locations, wherein depending on the computed instantaneous temperature distribution over the cast strip length or in a respective cross-section, which is under consideration, of the cast strip the coolant quantity or coolant distribution, particularly spray water quantity or spray water distribution, to be locally applied to the cast strip and the casting speed and the roller or segment adjustment are regulated in such a way that the desired structure or the desired structural composition is continuously, dynamically and constantly computed and set on-line and a desired position and formation of the end of the liquid phase and a desired geometric dimension or surface property or internal structure property of the cast strip (6) are set.
2. Method according to claim 1, characterised in that a desired macro-structure (= solidification structure) with a globulitic structure proportion of at least 30%, preferably at least 35%, and in the case of ferritic steel of at least 40%, preferably at least 45%, is set.
3. Method according to claim 1 or 2, characterised in that for setting the desired macro-structure in the case of a continuous casting plant equipped with an agitator the casting speed and the spray water quantity are regulated and in the case of a continuous casting plant with an adjustable agitator additionally the agitator position and agitation intensity, which are optimal with respect to attainment of the desired macro-structure and/or the desired structural composition of the cast strip (6), are set by means or on the basis of the simulation and computation model (21).
4. Method according to any one of the preceding claims, characterised in that for setting the desired micro-structure the simulation and computation model (21) comprises TTC (Time Temperature Conversion) diagrams and these are so combined with cast strip cooling rates calculated by means of an on-line temperature model of the cast strip (6) that for each defined computation element (16) of each cast strip cross-section the respective instantaneous cast strip cooling rate and the structural composition resulting therefrom can be and are computed and the desired structure is set by control of the cast strip cooling rates.
5. Method according to claim 4, characterised in that the cast strip cooling rates at the respective position thereof with respect to the cast strip (6) are so controlled and regulated through regulation of the coolant quantity, which is respectively incident on the cast strip (6) in this region, and/or control of the place or the area of incidence of the coolant (8, 11) on the cast strip (6) that a conversion of the metal structure on the narrow side (18) and/or the wide side (19) of the cast strip (6), particularly in the case of a steel strip, is achieved as uniformly as possible with avoidance of formation of deposition of ferrite grains on austenite grain boundaries.
6. Method according to claim 4 or 5, characterised in that the TTC (Time Temperature Conversion) diagrams are computed by means of the simulation and computation model (21).
7. Method according to one of more of claims 4 to 6, characterised in that the cast strip cooling rates are determined with respect to the narrow sides (18) of the cast strip (6) and the coolant quantity incident on the narrow sides (18) of the cast strip (6) and/or the place or area on which the coolant (8, 11) is applied to the respective narrow side (18) of the cast strip (6) is or are controlled and regulated in dependence on the structure arising in the boundary region with respect to the surface of the narrow side (18).
8. Method according to claim 1, characterised in that for setting the desired position and/or formation of the end of the liquid phase of the cast strip (6) a desired liquid phase length in the form of an SPDF (Solidification Point Difference Factor) value is calculated by means or on the basis of the simulation and computation model or models (21) and if a maximum SPDF_max value is exceeded the desired SPDF value is regulated towards and set by increasing the spray water quantity in the edge zones of the cast strip (6) in the region of the end of the liquid phase.
9. Method according to claim 1, characterised in that for setting the desired geometric dimension of the cast strip (6) by or on the basis of one or more calculation model(s) starting from the desired final thickness of the cast strip (6) at the plant's end to the mould along the length of the cast strip (6), the cooling rate necessary for achieving the desired dimension of the cast strip (6) and/or the adjustment causing a deformation for each segment and/or roll is calculated, controlled and set.
10. Method according to claim 9, characterised in that the segment adjustment and/or roller adjustment, which is or are to be set at each segment (29) for achieving a strip thickness respectively necessary for attainment of the desired final thickness, is or are computed by means of or on the basis of the simulation and computation model or models (21) from the density, which is determined from the respectively determined temperature or temperature distribution, and the resulting density difference over the cast strip length.
11. Method according to claim 1, characterised in that for setting the desired surface property or internal structure property of the cast strip and for avoidance of void locations or unconsolidated core locations a desired void diameter is computed by means of or on the basis of the simulation and computation model or models (21) over the cast strip length and the casting speed is reduced if a predetermined maximum value of the void diameter is exceeded.
12. Method according to any one of the preceding claims, characterised in that the method is used in the secondary cooling of the cast strip (6).

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