EP2209573B2 - Method for continuous austenitic rolling of a preliminary strip, which is produced in a continuous casting process - Google Patents

Description

The invention relates to a process for the continuous austenitic rolling of a pre-strip produced in a continuous casting process in a continuous casting plant with a casting thickness of less than 300 mm, preferably with a casting thickness of less than 150 mm, by thickness reduction steps in at least one of several successive rolling stands - Rolling mill to a hot strip with a Walzenddicke between 0.5 and 15 mm and subsequent transverse division of the rolled hot strip in waist sizes or bundle lengths before winding in a storage device.

Furthermore, the invention relates to a combined casting and rolling plant for the production of austenitic rolled hot strip in a continuous continuous casting and rolling process with a continuous casting for casting steel strands with a casting thickness of less than 300 mm, preferably for casting steel strands with a casting thickness of less as 150 mm, and with at least one rolling mill, which comprises a plurality of successive rolling stands, for producing a austenitic temperature range rolled hot strip with a Walzenddicke between 0.5 and 15 mm and a last mill downstream subdivision and strip storage device.

A process according to the invention for the continuous austenitic rolling of a pre-strip produced in a continuous casting process is to be understood as a process in which the pre-strip produced in a continuous casting line without pre-strip cutting section has a casting speed into the first rolling stand or the first rolling line and transport speed into each with a reduction in thickness subsequent rolling mill is introduced to produce hot strip. Likewise, the combined casting and rolling mill is configured in its structural configuration so that the cast pre-strip enters the first mill stand of the first mill train without a pre-strip parting cut at casting speed.

From the DE 38 40 812 A1 a combined casting and rolling process is known in which a steel strip cast in a continuous casting plant is rolled in two deformation steps directly from the casting heat and without a separating cut between the casting plant and the downstream rolling devices. A first rolling deformation of the cast steel strand takes place immediately after the solidification in the outlet region of the continuous casting plant with a single roll stand at a strand temperature of about 1100 ° C. The further rolling takes place in a multi-stand rolling train with a rolling speed which depends on the casting speed, which is a maximum of 5 m / min, and the degree of deformation achieved in the first rolling stand. To ensure a final rolling in the austenitic region, an inductive reheating of the steel strip between the first roll stand and the subsequent rolling train is absolutely necessary. Intermediate heating stages between the individual rolling mills of the rolling train are also provided.

From the WO 92/00815 A1 Furthermore, a combined casting and rolling process is known, in which a cast steel strand produced in a continuous casting plant is roll-formed without prior transverse division in two successive stages of deformation into a rollable material having cold rolling properties. A first Dikkenreduktion the cast steel strand is still within the continuous casting machine at a time in which the steel strand still has a liquid core (liquid core reduction). A second reduction in the thickness of the subsequently solidified steel strand takes place immediately after leaving the continuous casting machine in a multi-stand rolling mill at a strip temperature of about 1100 ° C. in the austenitic region. In the course of these two deformation stages, the steel strip of a casting thickness <100 mm is hot-rolled onto a coilable hot strip with a strip thickness of 10-30 mm.

From the WO 97/36699 A1 a method for the production of hot rolled steel strip is known in which the cast steel strand is fed without separating cut directly to a multi-stand rolling mill and finish rolled in the austenitic region. Here, a specific minimum number of deformation steps is proposed for a specific, relative to a slab width of 1.0 m volume flow, which is greater than 0.487 m ² / min, in order to ensure an austenitic final rolling safely. Due to different circumstances in the casting process, a steel strip temperature at the end of the continuous casting plant can no longer be ensured due to operational conditions, which no longer guarantees austenitic rolling in the last stand of the rolling train and can not be corrected by the homogenization before the first rolling stand. It has therefore been proposed in a procedural development, to provide additional heating or cooling units for adjusting any temperature characteristics of the rolled strip between two or more rolling mills of the rolling train. This very general definition for the positioning of appropriate heating and / or cooling units does not allow an optimal design of the rolling mill and the determination of the best possible grouping of rolling stands.

From the EP 0 823 294 A1 Furthermore, a method for producing a rolled steel strip of low carbon and ultra-low carbon steels in a continuous casting and rolling process is described in which also no separation cut is made between the casting process and the rolling process. The cast steel strip with a solidification thickness of more than 70 mm is austenitically rolled in a first deformation step in a temperature range of 1150 ° C - 900 ° C down to a strip thickness <20 mm. This is followed by an accelerated cooling to a temperature in the range of <738 ° C with subsequent ferritic rolling in at least three Rolling passes.

The object of the present invention is therefore to avoid the disadvantages of the known prior art and a method for the continuous austenitic rolling of a pre-strip produced in a continuous casting process with minimized capital expenditure by specifying the maximum number of scaffolds, intermediate heaters and / or heating powers and in dependence of proposed production and material indicators. These include, for example, the final roll thickness (of the strip to be wound) and the casting thickness and the austenite limit temperature defined by the chemical analysis.

Another object of the invention is to optimize the overall plant configuration for carrying out the rolling process based on an expected production spectrum under the constraint that slab thicknesses are from 30 to 150 mm and the composite production wide rate 2.5 to 4.5 t / min Hot strip, preferably 3.0 to 3.6 t / min (at a typical hot-plate density of 7.4 t / m ³ ) should be.

bestimmt wird, wobei

• T_VB,i [°C] die querschnittsgemittelte Vorbandtemperatur am Ende der Gießmaschine (im Bereich der Sumpfspitze) bzw. am Ende einer vor der i-ten Walzstraße installierten Zwischenerwärmungseinrichtung,
• T_aust [°C] die stahlgüteabhängige Austenitbildungs-Grenztemperatur (austenit. Endwalztemperatur),
• h_Br [mm] die Brammen-/Gießdicke bei Durcherstarrung (= Sumpfspitze),
• d _end,i [mm] die Banddicke nach den n_i Dickenreduktionsschritten, der i-ten Walzstraße,
• m_vor die Anzahl aller ab der Brammendurcherstarrung erfolgten Dickenreduktionsschritte bis zum Einlauf in das erste Gerüst der nachfolgenden i-ten Walzstraße,
• v_g [m/min] die Brammengießgeschwindigkeit

sind.This object is achieved in a method according to the preamble of claim 1, characterized in that the Vorband in each of the continuous casting mill downstream rolling mill with a number of n _i thickness reduction steps is reduced, wherein the number n _i to be performed thickness reduction steps by the condition $${\mathrm{n}}_{\mathrm{i}}\le \left\{\frac{T_{\mathit{VB}.i}-T_{\mathit{aust}}}{75}+{\mathrm{1.5.}}^{10}\log \left[\frac{H_{\mathit{br}}}{2^{\mathit{MVOR}}},{\left(\frac{1.4}{d_{\mathit{end}.i}}\right)}^{2.2},\frac{T_{\mathit{VB}.i}-T_{\mathit{aust}}}{T_{\mathit{aust}}}\right]\right\}\frac{\mathrm{7.4.}{H}_{\mathit{br}},v_G}{4000};n_{\mathrm{i}}\in \mathrm{N}$$

is determined, where

• T _{VB, i} [° C] is the cross-sectional average pre-strip temperature at the end of the casting machine (in the area of the sump tip) or at the end of an intermediate heating device installed in front of the i-th rolling line,
• T _aust [° C] the steel grade dependent austenite formation limit temperature (austenite finish rolling temperature),
• h _Br [mm] the slab / casting thickness when solidified (= sump tip),
• d _{end, i} [mm], the strip thickness after the n _i the thickness reduction steps, the i-th rolling mill,
• in _{front of} the number of all thickness reduction steps taken from the slab solidification until the entry into the first stand of the following i-th rolling train,
• v _g [m / min] is the slab casting speed

are.

With this calculation rule can be determined in a simple manner for a given steel quality at specified input and output conditions (tape formats, temperatures), the maximum number of required thickness reduction steps or rolling stands of a rolling mill, in which even in the last thickness reduction step or rolling mill of the rolling mill Rolling in the austenitic region is possible. And subsequently, how many intermediate heats and which intermediate heats are required to determine a given hot strip thickness, austenitic rolled throughout.

The term "rolling train" is to be understood as meaning the successive arrangement of a plurality of rolling stands, the stand spacing of adjacent rolling stands not exceeding 5.6 m, preferably 4.9 m, and no intermediate heating stage being arranged between adjacent rolling stands or an intermediate heating of the rolled strip taking place. Each rolling stand comprises a pair of work rolls.

Furthermore, it is also possible with this calculation rule to determine the number of necessary thickness reduction steps or the number of required rolling stands of several successively arranged rolling mills or groups of rolling mills, if between the individual rolling mills or groups of rolling mills interim heating devices are provided to increase the strip temperature. When the calculation rule is applied to a second or further rolling train arranged downstream of the continuous casting plant, all the already existing thickness reduction steps in the first rolling train (s) _are taken into account by the factor m, the original slab thickness h _{Br being} taken into account. Thus, even with multiple rolling mills or groups of rolling stands for each of these groups, the maximum reasonable number of thickness reduction steps can be determined. In the first of the continuous casting immediately downstream rolling mill applies m _before = 0, there still exist no upstream thickness reduction steps.

bestimmt. Dies bedeutet, dass die Anzahl der innerhalb jeder Walzstraße entsprechend den produktspezifischen Anforderungen aktivierten Dickenreduktionsschritte durch die beiden größten natürlichen Zahlen N aus der Menge der sich aus der mathematischen Bedingung ergebenden natürlichen Zahlen N bestimmt ist und aus diesen ausgewählt werden kann.Preferably, the number n of the thickness reduction steps activated within a rolling mill becomes the condition $$\begin{array}{l}\left\{\frac{T_{\mathit{VB}.i}-T_{\mathit{aust}}}{75}+{\mathrm{1.5.}}^{10}\log \left[\frac{H_{\mathit{br}}}{2^{\mathit{MVOR}}},{\left(\frac{1.4}{d_{\mathit{end}.i}}\right)}^{2.2},\frac{T_{\mathit{VB}.i}-T_{\mathit{aust}}}{T_{\mathit{aust}}}\right]\right\}\frac{\mathrm{7.4.}{H}_{\mathit{br}},v_G}{4000}-2\le n\le \\ \left\{\frac{T_{\mathit{VB}.i}-T_{\mathit{aust}}}{75}+{\mathrm{1.5.}}^{10}\log \left[\frac{H_{\mathit{br}}}{2^{\mathit{MVOR}}},{\left(\frac{1.4}{d_{\mathit{end}.i}}\right)}^{2.2},\frac{T_{\mathit{VB}.i}-T_{\mathit{aust}}}{T_{\mathit{aust}}}\right]\right\}\frac{\mathrm{7.4.}{H}_{\mathit{br}},v_G}{4000};\mathrm{}n\in N\end{array}$$

certainly. This means that the number of thickness reduction steps activated within each rolling train according to the product-specific requirements is determined by the two largest natural numbers N and can be selected from the set of natural numbers N resulting from the mathematical condition.

Thus, in an existing casting and rolling plant for continuous casting and austenitic rolling of steel strip, this method allows a determination of the optimum number of thickness reduction steps or rolling stands to be activated in each of the rolling mills downstream from the amount of existing rolling stands.

From thickness reduction step to thickness reduction step, there is a decrease in the cross-section-averaged pre-strip temperature, which must not be less than the austenite formation limit temperature dependent on steel content. In order to ensure that the steel-grade-dependent austenite formation limit temperature does not fall below even in the last thickness reduction step of a rolling train, after the reduction of thickness in a rolling train and before reduction of thickness in a subsequent rolling train, intermediate heating of the rolled strip takes place, whereby the cross-section averaged rolled strip temperature is 50 K to 450 K, preferably by 120 K to 350 K, is increased. This intermediate heating is preferably carried out by an inductive transverse field heating. However, other known methods for the implementation of the intermediate heating can be used, especially as a function of the intermediate strip thickness.

Preferably, with a casting thickness h _Br <45 mm, all thickness reduction steps in a rolling train and at a casting thickness h _Br > 60 mm, all required thickness reduction steps are carried out in at least two rolling mills. In the casting thickness range between 45 mm and 60 mm, rolling can be carried out in a rolling mill as well as in two rolling mills, depending on various influencing factors. For example, rolling in heavy plate production would preferably take place in one rolling line and preferably in two rolling lines during hot strip production.

It has been found to be expedient that, with a casting thickness h _Br <50 mm, all thickness reduction steps are carried out in a single rolling train without intermediate heating and at a casting thickness h _Br ≥ 50 mm, the required thickness reduction steps are carried out in at least two rolling mills.

For casting thicknesses below 50 mm and Walzbandenddicken over 3.5 mm, it is usually sufficient to provide a single rolling mill with a maximum of n rolling stands according to the calculation rule after the casting process and then cooling the band in a cooling section, according to the predetermined bundle weight schrosszuteilen and a winding system supply. An additional significant band heating is not necessary here.

In the case of a casting thickness of the preliminary strip of 50 mm and more, when determining the number of thickness reduction steps required to achieve the hot strip thickness to be coiled, it is usually the case that at least two groups of rolling stands are to be arranged, wherein the number of maximum necessary rolling stands for each group satisfies the conditions of Calculation rule fulfilled, ie The calculated number of reduction steps should by no means be overstated, but should tend to be undercut. Between the two groups of rolling stands, an intermediate heating of the pre-strip takes place by at least 50 K to a pre-strip temperature which is significantly higher than the austenite formation limit temperature. In any case, for the envisaged broad specific production rates of 2.5 to 4.5 t / min, preferably 3.0 to 3.6 t / min, a division into at least two groups of rolling stands is expedient if the final rolling thickness is less than 3.5 mm lies.

The method can be used advantageously if the preliminary strip produced in a continuous casting process is produced with a casting thickness of at least 30 mm, preferably with a casting thickness of at least 60 mm. The method is particularly advantageously applicable if, for casting thicknesses of 30 to 300 mm, preferably at casting thicknesses of 60 to 150 mm, a final rolling thickness of 0.5 to 15 mm, preferably from 0.8 to 12 mm and in particular from 1.0 to 8 mm, to be achieved.

als mathematisches Modell einem Prozessrechner auf einer Prozessleitebene zugeordnet ist und von diesem entsprechende Aktivierungssignale zur Aktivierung einzelner Walzgerüste einer oder mehrerer Walzstraßen an Einzelregelkreise der einen oder mehrerer Walzstraßen übermittelt werden, wobei Zustandsinformationen über den gegossenen Vorstreifen von einem Prozessrechner der vorgelagerten Stranggießanlage mitberücksichtigt werden und wahlweise insbesondere die erforderliche Temperatur T_vB'i' d.h die gemittelte Querschnittstemperatur des jeweiligen Vorbandes am Ende der Zwischenerwärmung vor der Walzstraße.To implement the method, it is expedient that the calculation rule for determining the number of n _i or n consecutive thickness reduction steps for each rolling mill based on the condition $$\begin{array}{l}\left\{\frac{T_{\mathit{VB}.i}-T_{\mathit{aust}}}{75}+{\mathrm{1.5.}}^{10}\log \left[\frac{H_{\mathit{br}}}{2^{\mathit{MVOR}}},{\left(\frac{1.4}{d_{\mathit{end}.i}}\right)}^{2.2},\frac{T_{\mathit{VB}.i}-T_{\mathit{aust}}}{T_{\mathit{aust}}}\right]\right\}\frac{\mathrm{7.4.}{H}_{\mathit{br}},v_G}{4000}-2\le n\le \\ \left\{\frac{T_{\mathit{VB}.i}-T_{\mathit{aust}}}{75}+{\mathrm{1.5.}}^{10}\log \left[\frac{H_{\mathit{br}}}{2^{\mathit{MVOR}}},{\left(\frac{1.4}{d_{\mathit{end}.i}}\right)}^{2.2},\frac{T_{\mathit{VB}.i}-T_{\mathit{aust}}}{T_{\mathit{aust}}}\right]\right\}\frac{\mathrm{7.4.}{H}_{\mathit{br}},v_G}{4000};\mathrm{}n\in N\end{array}$$

is associated with a process computer on a process control level as a mathematical model and from this corresponding activation signals for activating individual rolling stands of one or more rolling mills are transmitted to individual control loops of one or more rolling mills, wherein state information about the cast pre-strip of a process computer of the upstream continuous casting are taken into account and optionally in particular the required temperature T _{vB'i '} ie the average cross-sectional temperature of the respective Vorbandes at the end of the intermediate _heating before the rolling mill.

A combined caster and mill for the production of austenitic rolled hot strip in a continuous continuous casting and rolling process may include a continuous caster for casting steel cords having a casting thickness of less than 300 mm, preferably for casting steel cords having a casting thickness of less than 150 mm. and at least one rolling mill comprising a plurality of successive rolling mills for producing a hot rolled strip rolled in the austenitic temperature range with a rolling thickness of between 0.5 and 15.0 mm and a cutting plant and strip storage device arranged downstream of the last rolling stand.

The design of the combined casting and rolling plant is based on a future customer-oriented and coordinated intended production program for hot strip. An essential goal is to ensure a continuous exclusively austenitic rolling of a hot strip with a compact, wide production spectrum covering casting and rolling mill.

bestimmt wird, wobei

• T _VB,i [°C] die querschnittsgemittelte Vorbandtemperatur am Ende der Gießmaschine (im Bereich der Sumpfspitze) bzw. am Ende einer vor der i-ten Walzstraße installierten Zwischenerwärmungseinrichtung,
• T_aust [°C] die stahlgüteabhängige Austenitbildungs-Grenztemperatur (austenit. Endwalztemperatur),
• h_Br [mm] die Brammen-/Gießdicke bei Durcherstarrung (= Sumpfspitze),
• d_end,i [mm] die Banddicke nach den n_i Walzgerüsten/Dickenreduktionsschritten, der i-ten Walzstraße,
• m_vor die Anzahl aller ab der Brammendurcherstarrung aktivierten Walzgerüste / erfolgten Dickenreduktionsschritte bis zum Einlauf in das erste Gerüst der nachfolgenden i-ten Walzstraße,

sind.Each of the at least one rolling line may comprise a number of n _i immediately consecutive rolling stands, wherein the number of rolling stands n _i by the condition $${\mathrm{n}}_{\mathrm{i}}\le \left\{\frac{T_{\mathit{VB}.i}-T_{\mathit{aust}}}{75}+{\mathrm{1.5.}}^{10}\log \left[\frac{H_{\mathit{br}}}{2^{\mathit{MVOR}}},{\left(\frac{1.4}{d_{\mathit{end}.i}}\right)}^{2.2},\frac{T_{\mathit{VB}.i}-T_{\mathit{aust}}}{T_{\mathit{aust}}}\right]\right\};n_{\mathrm{i}}\in \mathrm{N}$$

is determined, where

• T _{VB , i} [° C] is the cross-sectional average pre-strip temperature at the end of the casting machine (in the area of the sump tip) or at the end of an intermediate heating device installed in front of the i-th rolling line,
• T _aust [° C] the steel grade dependent austenite formation limit temperature (austenite finish rolling temperature),
• h _Br [mm] the slab / casting thickness when solidified (= sump tip),
• _{dend, i} [mm] is the strip thickness after the n _i roll stands / thickness reduction steps, the ith rolling mill,
• m in _{front of} the number of all rolling stands activated from slab solidification / thickness reduction steps up to the entry into the first stand of the following i-th rolling train,

are.

bestimmt bzw. begrenzt. Dies bedeutet, dass die Anzahl der innerhalb jeder Walzstraße entsprechend den produktspezifischen Anforderungen vorgesehenen Walzgerüste durch die größte natürliche Zahl N aus der Menge der sich aus der mathematischen Bedingung ergebenden natürlichen Zahlen N bestimmt ist. Die Anwendung dieser Bedingung auf das bei der Anlagenprojektierung zugrundeliegende Produktspektrum ermöglicht eine optimierte Auslegung der Gesamtanlage.Preferably, the number n of rolling mills installed within a rolling mill is the condition $$\begin{array}{l}\frac{T_{\mathit{VB}.i}-T_{\mathit{aust}}}{75}+{\mathrm{1.5.}}^{10}\log \left[\frac{H_{\mathit{br}}}{2^{\mathit{MVOR}}},{\left(\frac{1.4}{d_{\mathit{end}.i}}\right)}^{2.2},\frac{T_{\mathit{VB}.i}-T_{\mathit{aust}}}{T_{\mathit{aust}}}\right]-1\le n\le \\ \frac{T_{\mathit{VB}.i}-T_{\mathit{aust}}}{75}+{\mathrm{1.5.}}^{10}\log \left[\frac{H_{\mathit{br}}}{2^{\mathit{MVOR}}},{\left(\frac{1.4}{d_{\mathit{end}.i}}\right)}^{2.2},\frac{T_{\mathit{VB}.i}-T_{\mathit{aust}}}{T_{\mathit{aust}}}\right];\mathrm{}n\in N\end{array}$$

determined or limited. This means that the number of rolling stands provided within each rolling mill in accordance with the product-specific requirements is determined by the largest natural number N from the set of natural numbers N resulting from the mathematical condition. The application of this condition to the product range underlying the system configuration enables an optimized design of the entire system.

To ensure austenitic rolling in the last roll stand of each of the optionally successive rolling mills, an intermediate heating device for raising the cross-section-averaged pre-strip temperature to T _{VB, i} to a correspondingly sufficient temperature level is arranged between each successive rolling train W _i-1 and W _i . In order to achieve the most uniform possible increase in the cross-section-averaged pre-strip temperature, the intermediate heating device is designed as a device for inductive transverse field heating.

The casting plant on which the combined casting and rolling plant is based comprises a continuous casting mold that can be set to different casting thicknesses or interchangeable continuous casting molds and a downstream strand guide with gap-adjustable strand segments. In the case of a continuous casting mold and strand guide set to a casting thickness h _Br <45 mm, it is expedient to activate exactly one rolling mill with n rolling stands and in the case of a continuous casting mold and strand guide set to a casting thickness hBr> 60 mm at least two rolling mills each having a specific number of rolling stands activated. In the casting thickness range between 45 mm and 60 mm, the rolling may be carried out in a rolling mill as well as in two rolling mills, depending on various influencing factors, with an intermediate heating device between the successive rolling mills.

According to a further possible embodiment it is advantageous that in the case of a cast thickness h _Br ≤ 50 mm set-ended mold and strand guide precisely a rolling mill with n roll stands is activated, and otherwise, at least two rolling trains, each having a certain number of roll stands, are enabled.

Depending on, in particular, the reduction in thickness envisaged in the individual rolling mills of the rolling mills and the thermal or thermodynamic state of the pre-strip or intermediate strip, it is expedient for the work-roll diameter of the work rolls in the first rolling line after the casting plant to have a diameter range of 650 mm to 980 mm is to achieve the greatest possible thickness reductions at very high slab temperatures or pre-strip temperatures. A preferred range of working roll diameters is between 650 mm and 800 mm. The working roll diameter of the work rolls in the second rolling line after the caster is in a diameter range of 500 mm to 870 mm, since the intermediate strip thickness is already lower. A preferred range of working roll diameters for this case is between 500 mm and 720 mm. In general, the working roll diameter should decrease when the inlet thickness of the rolling stock is lower.

Fig. 1

einen Längsschnitt einer kombinierten Gieß- und Walzanlage nach einer ersten Ausführungsform der Erfindung,

Fig. 2

einen Längsschnitt einer kombinierten Gieß- und Walzanlage nach einer zweiten Ausführungsform der Erfindung,

Fig. 3

einen Längsschnitt einer kombinierten Gieß- und Walzanlage nach einer dritten Ausführungsform der Erfindung

Fig. 4

Regelschema für die Steuerung der kombinierten Gieß- und Walzanlage.

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

Fig. 1

a longitudinal section of a combined casting and rolling plant according to a first embodiment of the invention,

Fig. 2

a longitudinal section of a combined casting and rolling plant according to a second embodiment of the invention,

Fig. 3

a longitudinal section of a combined casting and rolling mill according to a third embodiment of the invention

Fig. 4

Control scheme for the control of the combined casting and rolling plant.

In the FIGS. 1 to 3 Several possible embodiments of a combined casting and rolling plant are shown, which comprises a continuous casting plant for continuous casting of a steel strand with thin slab or center slab cross section and an immediately following rolling mill W for austenitic rolling of the cast strand or Vorbandes. The continuous casting machine G of conventional design according to the prior art is indicated by a continuous mold 3 and a strand guide 4 with strand guide rollers 5. The continuous casting mold 3 with subsequent strand guide determines the casting thickness h _{Br of} the pre-strip 6, which is fed immediately after a deflection of a substantially vertical casting direction in a horizontal transport direction of the rolling train W or facultative previously passes through a homogenizer 7, in which a homogenization of the temperature distribution in Support could be sought. The pre-strip 6 with the casting thickness h _Br occurs - without a separating cut is performed - with casting speed v _g and with a cross-section-averaged pre-strip temperature T _{VB, 1} in the first roll stand 8a of the rolling train W. The number of rolling stands 8a, 8b,..., 8n used in the rolling train W is determined by the desired final thickness, d _{end, 1} and by the final rolling temperature in the rolling stand 8n, which must necessarily exceed the steel-grade-dependent austenite formation limit temperature T _aust . The number n _{1 of} the maximum usable rolling stands for a specific steel grade with certain geometric default values is determined by the general formula $${\mathrm{n}}_{\mathrm{i}}\le \frac{T_{\mathit{VB}\mathrm{,1}}-T_{\mathit{aust}}}{75}+{\mathrm{1.5.}}^{10}\log \left[\frac{H_{\mathit{br}}}{2^{\mathit{MVOR}}},{\left(\frac{1.4}{d_{\mathit{end}.i}}\right)}^{2.2},\frac{T_{\mathit{VB}.i}-T_{\mathit{aust}}}{T_{\mathit{aust}}}\right];n_{\mathrm{i}}\in {\mathrm{N\; and}}_{\mathrm{i}}=1.$$

The number of rolling stands results from the largest natural number in the field of possible result values.

Subsequently, the hot-rolled strip passes through a cooling section 9, is divided according to predetermined bundle weights with a dividing line 10 formed by a dividing shears 10 and wound in a band reeling device 11 in coils.

The output strand thickness determined in the continuous casting plant and the desired final rolling thickness of the hot strip wound into a bundle determine not only the steel quality but also the number of necessary rolling stands / thickness reduction steps in order to achieve an end product with the required material and structural properties. The cross-section-averaged pre-strip temperature T _{VB, 1} at the end of the casting machine and thus before entry into the first roll stand is variable only within very narrow limits and depends on the operating conditions of the continuous casting machine. The steel grade dependent austenite formation limit temperature is a material constant that is essentially fixed for each grade of steel. During the rolling process, on the one hand, deformation energy is released in the form of heat; on the other hand, the pre-strip gives off heat to the environment on its way through the rolling stands. In sum, the pre-strip temperature usually decreases continuously, and the greater the lower the rolling speed, or the input side, the casting speed. The above-mentioned, developed formula provides the determination of the max. meaningful number of rolling stands or thickness reduction steps to be made in a rolling train, wherein the strip temperature does not fall below the austenite formation limit temperature in the rolling mill, taking into account all Vorverformungsschritte. If the aim is slab thicknesses> 50 mm rolling thicknesses <3.5 mm, the arrangement of two or more rolling mills W1, W2, W3 is necessary, as in the embodiments according to Figures 2 and 3 shown.

The combined casting and rolling plant in the embodiment according to FIG. 2 agrees in the basic approaches with the embodiment described above FIG. 1 match. Instead of the rolling train W according to FIG. 1 Now two consecutive, separated by an intermediate heating device 12 rolling mills W1 and W2 are provided.

The rolling train W1 comprises a certain maximum number of rolling stands 8a, 8b,..., 8n, which is to be determined with the calculation rule given above. Similarly, the rolling train W2 has a certain maximum number of rolling stands 13a, 13b, ..., 13m, which is also to be determined with the above-mentioned calculation rule, wherein for W _2, the number of already in the rolling mill W1 made thickness reduction steps in the Calculation rule by the exponent m _before to take into account. In the intermediate heater 12, the cross-sectional averaged temperature of the pre-strip is again brought to a sufficiently high temperature level above the austenite formation limit temperature of the pre-strip reduced in the rolling train W1 to perform the austenitic rolling passes in the rolling train W2. The temperature increase achieved with the intermediate heating device is dependent on demand in the range of 50 K up to 450 K, preferably in the range of 120 K to 350 K.

In the FIG. 3 schematically illustrated combined casting and rolling plant is equipped with three rolling mills W1, W2 and W3 and particularly suitable if starting from a relatively large casting thickness (eg.> 150 mm) and long metallurgical strand guide length, or relatively low averaged slab temperature T _VB austenitic rolled Hot strip with a very low roll thickness (eg <1.2 mm) to be produced. Between the rolling train W1 with the rolling stands 8a, ..., 8n and the rolling train W2 with the rolling stands 13a, ... 13m is an intermediate heating device 12 and between the rolling train W2 and the rolling train W3 with the rolling stands 15a, 15b, ... 15o, another intermediate heating device 14 is arranged. The determination of the number of rolling mills required in the rolling train W3 is analogous to the determination of the maximum number of rolling mills in the rolling train W2. However, in the calculation rule for the rolling train W ₂ in the case of the exponent m _, all pre-deformation stages in the rolling mills W _{1 and} W _{2 are} to be taken into account.

wobei die Anzahl der Dickenreduktionsschritte für jede Walzstraße aus den beiden größten natürlichen Zahlen aus der Menge der natürlichen Zahlen wählbar ist, die sich aus der Bedingung ergeben.In commercial practice, it is necessary to produce hot strip in different steel grades and with very different final rolling thicknesses from steel strands with different casting thicknesses. A multi-layered product range can be produced very easily on a combined casting and rolling plant of the type according to the invention if an arrangement of the rolling mills has already been arranged in the conceptual phase of the plant production for this product range. As a result, a product-specific activation of required rolling stands is possible. Therefore, the plant will usually actually the respective maximum number of stands in each rolling mill, depending on max. Slab thickness, minimum ribbon take-up thickness, the respective intermediate strip thicknesses d _{end, i,} and the intermediate heating temperatures T _{VB, i} according to the developed formula and intermediate heating means. In addition, operational temperature variations in the production of the pre-strip in the continuous casting can be achieved by appropriate control of the rolling mills in particular, by activating an optimal roll stand configuration. This can take place on the process control level P, which receives corresponding status information from a process computer PS of the upstream continuous casting plant and transmits activation signals to the individual control loops PW1 and PW2 of the rolling mills W1 and W2 ( Fig. 4 ). The special calculation rule is assigned here as a mathematical model to the process computer at the process control level, whereby the current average or steady-state mass-specific mass flow rate is to be included as a multiplication factor. For this case, the number of thickness reduction steps in the individual stands is determined according to the condition $${\mathrm{n}}_{\mathrm{i}}\le \left\{\frac{T_{\mathit{VB}.i}-T_{\mathit{aust}}}{75}+{\mathrm{1.5.}}^{10}\log \left[\frac{H_{\mathit{br}}}{2^{\mathit{MVOR}}},{\left(\frac{1.4}{d_{\mathit{end}.i}}\right)}^{2.2},\frac{T_{\mathit{VB}.i}-T_{\mathit{aust}}}{T_{\mathit{aust}}}\right]\right\}\frac{\mathrm{7.4.}{H}_{\mathit{br}},v_G}{4000}{\mathrm{;\; n}}_{\mathrm{i}}\in \mathrm{N}$$

wherein the number of thickness reduction steps for each rolling train is selectable from the two largest natural numbers from the set of natural numbers resulting from the condition.

The intermediate heating device 12 is integrated into the control loop at the process control level P.

Claims (9)

1. Method for the continuous austenitic rolling of a preliminary strip, which is produced in a continuous casting process in a continuous casting facility with a casting thickness of less than 300 mm, preferably with a casting thickness of less than 150 mm, by performing thickness reduction steps in at least one rolling train - formed by a plurality of successive rolling stands - to form a hot strip having a final rolling thickness of between 0.5 and 15 mm and subsequent transverse separation of the rolled hot strip into coil sizes or coil lengths before winding in a storage device, characterized in that the preliminary strip (6) is reduced in thickness in each of the rolling trains (W, W1, W2, W3) downstream of the continuous casting facility by a number (n, n₁, n_i) of thickness reduction steps, the number n_i of thickness reduction steps to be carried out being determined by the condition $${\mathrm{n}}_{\mathrm{i}}\le \left\{\frac{T_{\mathit{VB},i}-T_{\mathit{aust}}}{75}+{\mathrm{1,5.}}^{10}\log \left[\frac{h_{\mathit{Br}}}{2^{\mathit{mvor}}}.{\left(\frac{\mathrm{1,4}}{d_{\mathit{end},i}}\right)}^{\mathrm{2,2}}.\frac{T_{\mathit{VB},i}-T_{\mathit{aust}}}{T_{\mathit{aust}}}\right]\right\}\frac{\mathrm{7,4}\ast h_{\mathit{Br}}\ast v_g}{4000}{\mathrm{;\; n}}_{\mathrm{i}}\in \mathrm{N}$$

   

   where

   T_VB,i [ºC] is the cross-sectionally averaged preliminary strip temperature at the end of the casting machine (in the region of the liquidus tip) or at the end of an intermediate heating device installed before the i^th rolling train,

   T_aust [ºC] is the steel quality-dependent austenite formation limit temperature (austenitic final rolling temperature),

   h_Br [mm] is the slab/casting thickness at solidification (=liquidus tip),

   d_end,i [mm] is the strip thickness after the n_i thickness reduction steps of the i^th rolling train,

   m_vor is the number of all thickness reduction steps carried out from the slab solidification until entry into the first stand of the subsequent i^th rolling train,

   v_g [m/min] is the slab casting speed.
2. Method according to Claim 1, characterized in that the number n of thickness reduction steps activated inside a rolling train is determined by the condition $$\begin{array}{l}\left\{\frac{T_{\mathit{VB},i}-T_{\mathit{aust}}}{75}+{\mathrm{1.5.}}^{10}\log \left[\frac{h_{\mathit{Br}}}{2^{\mathit{mvor}}}.{\left(\frac{\mathrm{1,4}}{d_{\mathit{end},i}}\right)}^{2.2}.\frac{T_{\mathit{VB},i}-T_{\mathit{aust}}}{T_{\mathit{aust}}}\right]\right\}\frac{\mathrm{7.4.}{h}_{\mathit{Br}}.v_g}{4000}-2\le n\le \\ \left\{\frac{T_{\mathit{VB},i}-T_{\mathit{aust}}}{75}+{\mathrm{1.5.}}^{10}\log \left[\frac{h_{\mathit{Br}}}{2^{\mathit{mvor}}}.{\left(\frac{\mathrm{1,4}}{d_{\mathit{end},i}}\right)}^{2.2}.\frac{T_{\mathit{VB},i}-T_{\mathit{aust}}}{T_{\mathit{aust}}}\right]\right\}\frac{\mathrm{7.4.}{h}_{\mathit{Br}}.v_g}{4000};\mathrm{}n\in N\end{array}.$$

   
3. Method according to Claim 1 or 2, characterized in that intermediate heating of the rolling strip is performed after carrying out thickness reduction steps in a rolling train (W1 or W2) and before carrying out thickness reduction steps in a subsequent rolling train (W2 or W3), the cross-sectionally averaged rolling strip temperature being increased by from 50 K to 450 K, preferably by from 120 to 350 K.
4. Method according to Claim 3, characterized in that the intermediate heating is carried out by inductive transverse field heating.
5. Method according to one of the preceding Claims 1 to 4, characterized in that for a casting thickness h_Br < 45 mm all the thickness reduction steps are carried out in one rolling train, and for a casting thickness h_Br > 60 mm all necessary thickness reduction steps are carried out in at least two rolling trains.
6. Method according to one of the preceding claims, characterized in that for a casting thickness h_Br < 50 mm all the thickness reduction steps are carried out in one rolling train, otherwise the necessary thickness reduction steps are preferably carried out in at least two rolling trains.
7. Method according to one of the preceding claims, characterized in that the rolling thickness of the hot strip lies between 0.8 and 12 mm, preferably between 1.0 mm and 8 mm.
8. Method according to one of the preceding claims, characterized in that the preliminary strip produced in a continuous casting process is produced with a casting thickness of at least 30 mm, preferably with a casting thickness of at least 60 mm.
9. Method according to one of the preceding claims, characterized in that a calculation rule for determining the number n_i or n of immediately successive thickness reduction steps for each rolling train is assigned on the basis of the condition $$\begin{array}{l}\left\{\frac{T_{\mathit{VB},i}-T_{\mathit{aust}}}{75}+{\mathrm{1,5.}}^{\ast }\log \left[\frac{h_{\mathit{Br}}}{2^{\mathit{mvor}}}\ast {\left(\frac{\mathrm{1,4}}{d_{\mathit{end},i}}\right)}^{2.2}\ast \frac{T_{\mathit{VB}.i}-T_{\mathit{aust}}}{T_{\mathit{aust}}}\right]\right\}\frac{\mathrm{7,4}\ast h_{\mathit{Br}}\ast v_g}{4000}-2\le n\le \\ \left\{\frac{T_{\mathit{VB},i}-T_{\mathit{aust}}}{75}+{\mathrm{1,5.}}^{\ast }\log \left[\frac{h_{\mathit{Br}}}{2^{\mathit{mvor}}}*{\left(\frac{\mathrm{1,4}}{d_{\mathit{end},i}}\right)}^{2.2}\ast \frac{T_{\mathit{VB}.i}-T_{\mathit{aust}}}{T_{\mathit{aust}}}\right]\right\}\frac{\mathrm{7,4}\ast h_{\mathit{Br}}\ast v_g}{4000};\mathrm{}n\in N\end{array}$$

   

   as a mathematical model to a process computer on a process management level (P), and corresponding activation signals for activating individual rolling stands (8a, 8b,..., 8n; 13a, 13b, ..., 13m; 15a, 15b, ..., 150) of one or more rolling trains (W, W1, W2, W3) are transmitted by the latter to the individual control loops (PW1, PW2) of the one or more rolling trains, status information concerning the cast preliminary strip from a process computer (PS) of the preceding continuous casting facility being jointly taken into account, and optionally in particular the required temperature T_VB,i, i.e. the averaged cross-sectional temperature of the respective preliminary strip at the end of the intermediate heating before the rolling train.

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