Rolling of steel with measured detection of the phase transition

Abstract

A strip (2) of steel is rolled in a rolling stand (3) of a rolling mill (1). During the rolling of successively rolled sections (10) of the strip (2), values are measured that are characteristic of the rolling force (FW) and / or the rolling moment (M) occurring. A gradient (G) of the rolling force (FW) and / or the rolling moment (M) relative to the temperature (T) is determined by utilising the rolling forces (FW) and / or rolling moments (M) that occur and changes (δT) in the associated temperatures (T) of the sections (10) of the strip (2). The gradient (G) is used to determine whether or not a phase transition from an austenitic to a ferritic microstructure occurs in the sections (10) of the strip (2) during rolling in the rolling stand (3).

Description

[0001] Description

[0002] Title of the invention

[0003] Rolling of steel with measurement of phase transformation

[0004] field of technology

[0005] The present invention is based on an operating method for at least one rolling stand of a rolling mill for rolling a steel strip,

[0006] - wherein, during the rolling of successively rolled sections of the strip in the rolling stand, characteristic values ​​for the rolling force and / or the rolling moment occurring are measured in each rolling pass.

[0007] The present invention is further based on a control program for a control device of a rolling mill comprising at least one rolling stand for rolling a steel strip, wherein the control program comprises machine code which can be processed by the control device, wherein the processing of the machine code by the control device causes the control device

[0008] - during the rolling of successively rolled sections of the strip in the rolling stand, during each rolling pass, receives measured values ​​which are characteristic of the rolling force and / or the rolling moment occurring.

[0009] The present invention further relates to a control device of a rolling mill for rolling a steel strip, wherein the control device is programmed with such a control program, so that the control device carries out such an operating method during operation.

[0010] The present invention further relates to a rolling mill for rolling a strip of steel,

[0011] - wherein the rolling mill comprises at least one rolling stand in which sections of the strip are rolled one after the other,

[0012] - wherein the rolling stand is assigned a detection device for measuring values ​​which are characteristic of the rolling force occurring during rolling of the strip sections and / or the rolling torque occurring during rolling of the strip sections,

[0013] - wherein the rolling mill has a control device controlling the rolling stand,

[0014] - that the control device is connected to the recording device for receiving the measured values. State of the art

[0015] The aforementioned items are generally known. In particular, Steckel rolling mills and multi-stand finishing trains, both for rolling steel strip, are operated and designed in this way.

[0016] US Pat. No. 8,145,346 B2 discloses continuously updating the physical condition of a rolled stock during rolling. This involves first determining an initial condition.

[0017] The condition is cyclically updated using a model based on measured variables. The measured variables can include temperature, rolling force, and rolling torque.

[0018] DE 196 00 990 A1 discloses first rolling a rolled stock in an austenitic state, then cooling it to cause the phase transformation to ferrite, and then rolling it in a ferritic state. Cooling serves the purpose of avoiding the temperature range during rolling in which the rolled stock is mixed austenitic and ferritic.

[0019] Summary of the invention

[0020] When rolling steel, it is advisable or even necessary - depending on the specific plant configuration and the desired product - for the strip to have a ferritic or at least partially ferritic microstructure during rolling. This may be particularly necessary during the last rolling pass or passes of finish rolling. However, it is difficult to determine exactly when the transformation of the microstructure from austenite to ferrite begins or ends. This is especially true if the strip is cooled again before rolling, for example by means of so-called power cooling. During power cooling, the water is sprayed onto the strip at a high pressure of several bar, whereas with laminar cooling it is applied to the strip at a low pressure, usually below 1 bar.

[0021] In the current state of the art, the determination is usually carried out using thermo-kinetic models that model both the temperature behavior of the strip and its forming behavior. However, this modeling is subject to many inaccuracies. For example, in a multi-stand finishing mill, the temperature is often measured upstream of a descaler or a cooling unit, with the descaler or cooling unit being located upstream of the finishing mill. From the time the temperature is recorded, only a model-based calculation of the temperature is carried out. The further this modeling progresses, the more errors can occur. Furthermore, input variables that influence the modeling are often not precisely known. An example of such an input variable could be the chemical composition of the steel. Regardless of the exact situation, however, model-based determination is always subject to certain errors.The object of the present invention is to create possibilities by means of which it is possible to determine with high accuracy which structure sections of the strip have during rolling in a rolling stand.

[0022] The object is achieved by an operating method having the features of claim 1. Advantageous embodiments of the operating method are the subject of dependent claims 2 to 6.

[0023] According to the invention, an operating method of the type mentioned at the outset is designed in that

[0024] - that by utilising the rolling forces and / or rolling moments occurring during the rolling of the strip sections in the rolling stand, determined by the measured values, and changes in the associated temperatures of the strip sections, a gradient of the rolling force and / or rolling moment relative to the temperature is determined and

[0025] - that the gradient is used to determine whether or not a phase transformation from an austenitic to a ferritic structure occurs in the sections of the strip during rolling in the rolling stand.

[0026] The present invention is based on the fact that, on the one hand, the rolling force required to roll a section of the strip becomes smaller the hotter the corresponding section is. This applies to both an austenitic and a ferritic structure. However, a considerably lower rolling force is required to form a ferritic structure than to form an austenitic structure. On the other hand, since an austenitic structure exists at high temperatures and a ferritic structure at low temperatures, two opposing effects overlap during cooling. On the one hand, the rolling force increases initially under otherwise constant conditions. On the other hand, the proportion of ferrite increases and the proportion of austenite decreases during cooling. Increasing the proportion of ferrite and decreasing the proportion of austenite result in a reduction in the rolling force.

[0027] As a result, the latter effect predominates. As a result, in the transformation range in which the phase transformation from austenite to ferrite occurs, the rolling force also decreases as the temperature drops. This results in a positive gradient of the rolling force relative to the temperature, i.e. a decreasing rolling force with decreasing temperature and an increasing rolling force with increasing temperature. This is in contrast to rolling a purely austenitic microstructure. Here, a negative gradient of the rolling force relative to the temperature results, i.e. an increasing rolling force with decreasing temperature and a decreasing rolling force with increasing temperature. The same applies when rolling a purely ferritic microstructure. Thus, based on the sign of the gradient, it can be determined whether a phase transformation from an austenitic to a ferritic microstructure is occurring in the sections of the strip during rolling in the rolling stand.The other rolling conditions, such as the chemical composition of the strip, the dimensions of the strip, the pass reduction and the rolling speed, must of course not change.

[0028] The rolling force and the rolling moment are closely linked. This coupling results in a similar situation for the rolling moment.

[0029] As a result, during hot rolling of the strip it can be determined whether rolling is taking place in the transition area in which the phase transformation from an austenitic to a ferritic structure occurs.

[0030] The essential advantage of the procedure according to the invention is that it is not a modeling exercise with all its unavoidable uncertainties, but rather that, based on measured values, a reliable decision can be made as to whether or not a phase transformation from an austenitic to a ferritic structure occurs in the sections of the strip during rolling in the rolling stand.

[0031] It is possible that the temperature changes of the sections are known based on modeled or otherwise specified data. Preferably, however, the temperature changes of the sections are determined or estimated based on a temperature measured before or after rolling. For example, a temperature can be measured for each section before rolling, and the temperature during rolling can be determined or estimated from this. The temperatures of the sections themselves then naturally also provide information about their changes from section to section or relative to a (in principle, arbitrary) reference temperature.

[0032] If temperature measurement is performed before and / or after rolling in a multi-stand rolling mill, the temperature measurement can - exceptionally - be performed immediately before or after each rolling stand. However, such temperature measurement is generally only performed before the first rolling stand of the rolling mill and / or after the last rolling stand of the rolling mill.

[0033] As a rule, a strip is not rolled in a single rolling pass, but in a whole sequence of rolling passes carried out consecutively by at least one rolling stand of the rolling mill. This applies, on the one hand, to rolling in a reversing stand, in which one and the same rolling stand carries out several passes in succession, for example, a Steckel rolling mill. On the other hand, this also applies to rolling in a multi-stand rolling mill, whose rolling stands the strip passes through one after the other, with each rolling stand carrying out a single rolling pass, typically a finishing mill. The multi-stand rolling mill can be part of a combined casting and rolling plant, in which the strip – whether continuous or in the form of individual slabs – is fed to the rolling mill directly from the casting heat. In both a reversing stand and a multi-stand rolling mill, it is preferably provided

[0034] - that by comparing the gradients determined for the individual rolling passes, it is determined at which of the rolling passes a phase transformation from an austenitic to a ferritic structure occurs for the first time and / or at which of the rolling passes a phase transformation from an austenitic to a ferritic structure occurs for the last time, and

[0035] - that the operating parameters of the rolling mill are varied depending on the first and / or last rolling pass in which a phase transformation from an austenitic to a ferritic structure occurs.

[0036] If the method is carried out for several rolling passes carried out one after the other, it is particularly possible to adjust the operating parameters of the rolling mill in such a way that the rolling pass in which a phase transformation from an austenitic to a ferritic structure occurs for the first time or for the last time is a predetermined rolling pass in the sequence of rolling passes.

[0037] If, for example, several rolling passes are carried out one after the other (e.g., seven rolling passes), the operating parameters of the rolling mill can be adjusted so that the first rolling pass in the sequence of rolling passes is the rolling pass in which a phase transformation from an austenitic to a ferritic structure occurs for the first time or last time, or so that at least the last rolling pass in the sequence of rolling passes is not carried out until the phase transformation from an austenitic to a ferritic structure has been fully completed. It is even possible to vary the operating parameters so that the phase transformation from an austenitic to a ferritic structure is already completed before the first rolling pass in the sequence of rolling passes. Of course, other approaches are also possible.

[0038] All controllable operating variables that allow for the start and end of the phase transformation can be considered as operating parameters of the rolling mill. Typical operating parameters include:

[0039] - the extent to which the strip is heated in an upstream furnace (e.g. an induction furnace) before rolling,

[0040] - the extent to which the strip is cooled in an upstream cooling device before rolling,

[0041] - the extent to which the strip is heated and / or cooled between individual rolling passes (for example, in the case of cooling in a multi-stand rolling mill by so-called inter-stand cooling),

[0042] - possibly a change in the schedule and

[0043] - possibly a change in rolling speed. It is also possible for the operating parameters of the rolling mill to be adjusted in such a way that a specified energy consumption of the rolling mill is minimized, the productivity of the rolling mill is maximized, a rolling force and / or a rolling torque of at least one of the rolling passes performed by at least one of the rolling stands is reduced, and / or a product property of the strip is optimized after the sequence of rolling passes has been completed.

[0044] The specified energy consumption can be the energy consumption of a single rolling stand, the energy consumption of all rolling stands or rolling passes, the energy consumption of units upstream and / or downstream of the rolling stand(s) (e.g., an induction furnace upstream of the rolling stand(s), a cooling unit upstream of the rolling stand(s), and / or a cooling section downstream of the rolling stand(s). Any combination of these can also be considered.

[0045] If no phase transformation from an austenitic to a ferritic structure occurs in a particular rolling pass, the sections of the strip in the rolling stand are rolled either austenitically or ferritically in that particular rolling pass. If no phase transformation from an austenitic to a ferritic structure occurs, a decision is preferably made as to whether the sections of the strip in the rolling stand are rolled austenitically or ferritically in that particular rolling pass. Furthermore, an adaptation of a model for rolling the strip is preferably dependent on this decision. This dependency may mean that the model is adapted in one case but not in the other. Above all, however, this may mean that the model is adapted in both cases, but in a different way than in the other case. For example, due to the distinction made between cases, a respective model in which an austenitic or ferritic structure is used canferritic rolling is modeled, can be adapted independently of the other model.

[0046] The decision as to whether the strip sections in the rolling stand are to be rolled austenitically or ferritically can be made easily, particularly if the two rolling passes in which a phase transformation from an austenitic to a ferritic structure occurs for the first time and for the last time are known. Specifically, austenitic rolling occurs in those rolling passes that are carried out before the rolling pass in which a phase transformation from an austenitic to a ferritic structure occurs for the first time. Conversely, ferritic rolling occurs in those rolling passes that are carried out after the rolling pass in which a phase transformation from an austenitic to a ferritic structure occurs for the last time. The problem is further solved by a control program having the features of claim 7.According to the invention, the processing of the control program causes the control device - in addition to receiving the measured values ​​characteristic of the rolling force occurring -.

[0047] - by using the rolling forces and / or rolling moments occurring during the rolling of the strip sections determined by the measured values ​​and the changes in the associated temperatures of the strip sections known to the control device, a gradient of the rolling force and / or rolling moment relative to the temperature is determined and

[0048] - based on the gradient, it is determined whether or not a phase transformation from an austenitic to a ferritic structure occurs in the sections of the strip during rolling in the rolling stand.

[0049] As a result, an operating method according to claim 1 is realized due to the execution of the control program by the control device. The same advantages also result.

[0050] The control program can be designed in the same way as the operating procedure, offering the same advantages.

[0051] The object is further achieved by a control device having the features of claim 13. According to the invention, the control device is programmed with a control program according to the invention, so that the control device executes an operating method according to the invention during operation.

[0052] The object is further achieved by a rolling mill having the features of claim 14. According to the invention, in a rolling mill of the type mentioned at the outset, the control device of the rolling mill is designed as a control device according to the invention.

[0053] In an advantageous embodiment of the rolling mill, the control device is connected by data technology to a device for specifying the temperatures of the sections of the strip or changes therein and / or the control device is connected by data technology to a temperature measuring station arranged upstream or downstream of the rolling stand for measuring the temperature of the sections.

[0054] Short description of the drawings

[0055] The above-described properties, features, and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more readily understood in connection with the following description of an embodiment, which is explained in more detail in conjunction with the drawings.

[0056] FIG 1 a rolling mill,

[0057] FIG 2 a band,

[0058] FIG 3 a flow chart,

[0059] FIG 4 shows a section of the rolling mill of FIG 1 ,

[0060] FIG 5 a temperature-rolling force diagram,

[0061] FIG 6 shows a section of FIG 5,

[0062] FIG 7 a flow chart,

[0063] FIG 8 shows another flow chart and FIG 9 shows another flow chart.

[0064] Description of the embodiments

[0065] According to FIG. 1, a strip 2 is being rolled in a rolling mill 1. Strip 2 is made of steel. Rolling in rolling mill 1 is hot rolling.

[0066] For rolling the strip 2, the rolling mill 1 according to FIG 1 comprises a plurality of rolling stands 3 in which the strip 2 is rolled sequentially one after the other in a corresponding number of rolling passes. The number of rolling stands 3 can, for example, be between 3 and 7. FIG 1 only shows the work rolls of the rolling stands 3. However, the rolling stands 3 are generally designed as four-high stands or six-high stands, i.e., in addition to the work rolls, they have at least backup rolls, and optionally also intermediate rolls arranged between the work rolls and the backup rolls. Various devices can be arranged upstream of the rolling stands 3. Purely by way of example, FIG 1 shows a furnace 4 (for example an induction furnace), a descaling device 5 and a cooling unit 6. Furthermore, various devices can be arranged downstream of the rolling stands 3. Purely by way of example, FIG 1 shows a cooling section 7, a shear 8 and a coiler 9.The upstream and / or downstream devices 4 to 9 can be regarded as components of the rolling mill 1.

[0067] The illustration in FIG. 1, in which the rolling mill 1 represents a finishing train, is purely exemplary. In particular, the upstream and downstream devices 4 to 9 can be present or absent as needed. Furthermore, multiple rolling stands 3 do not necessarily have to roll the strip 2 sequentially one after the other. Instead of multiple rolling stands 3, it would also be possible to provide only a single rolling stand 3 in which the strip 2 is rolled in a reversing manner in several rolling passes. In this case, the rolling mill 1 would be designed as a reversing stand, for example, a Steckel rolling mill. According to FIG 2, the band 2 comprises a plurality of sections 10. However, the subdivision of the band 2 into the sections 10 is only virtual, i.e. for the data processing of the band 2. The sections 10 can be defined, for example, by a clocked acquisition of data (for example every 50 ms to 500 ms, in particular every 200 ms to 400 ms).Alternatively, they can be defined by a specific length before rolling (e.g., 1 m) or a specific mass (e.g., 25 kg). Since strip 2 undergoes rolling passes sequentially, this also applies to the individual sections 10.

[0068] The rolling mill 1 has a control device 11. The rolling mill 1 and thus in particular each rolling stand 3 of the rolling mill 1 is controlled by the control device 11. The control device 11 is programmed with a control program 12. The control program 12 comprises machine code 13 that can be processed by the control device 11. The programming of the control device 11 with the control program 12 or the processing of the machine code 13 by the control device 11 causes the control device 11 to execute an operating method that is explained in more detail below in conjunction with FIGS. 3 and 4. The operating method is explained only for a single rolling stand 3 or a single rolling pass. However, it can be executed for each of the rolling stands 3 or for each rolling pass.

[0069] According to FIG 3, in a step S1, the control device 11 receives a value for a respective section 10 of the strip 2, which is characteristic of the temperature T of the respective section 10 during rolling in the rolling stand 3. For example, the rolling mill 1 according to FIG 1 can have a temperature measuring station 14 arranged upstream of the rolling stand 3 (in the case of a multi-stand rolling mill 3, the rolling stands 3 of the rolling mill). Alternatively or additionally, the rolling mill 1 according to FIG 1 can have a temperature measuring station 15 arranged downstream of the rolling stand 3 (in the case of a multi-stand rolling mill 3, the rolling stands 3 of the rolling mill). In this case, the corresponding temperatures T', T" of the sections 10 are measured before or after the rolling of the sections. Alternatively, the corresponding temperatures T can be specified to the control device 11 according to FIG 1 by another device 16, for example a higher-level computer.In any case, the control device 11 is connected to the corresponding temperature measuring station 14, 15 or the device 16 via data communication.

[0070] Based on the measured temperatures T', T" or otherwise predetermined temperatures T, the control device 11 determines or estimates in a step S2 a change in the ΔT of the temperature T of the respective section 10 of the belt 2 compared to an initial value or reference value. For example, the temperature T for the first section 10 of the belt 2 can represent the initial value or reference value. For the first section 10 of the belt 2, the change ΔT of the temperature T thus has the value 0. For each additional section 10 of the belt 2, the change ΔT of the temperature T results from the difference between the respective temperature T and the temperature T of the first section 10 of the belt 2.

[0071] In the simplest case, the measured temperature T', T" or the specified temperature T can be adopted directly. However, other procedures are also possible. For example, using a model, the corresponding temperature T for the time at which the corresponding section 10 is rolled in the rolling stand 3 can be determined on the basis of the respective measured temperature T', T". In this case, too, the temperature T determined in this way can represent the initial value or reference value for the first section 10 of the strip 2, and for each further section 10 of the strip 2, the change ÖT in the temperature T can be determined using the difference between the respective temperature T and the temperature T of the first section 10 of the strip 2.

[0072] In a step S3, the control device 11 receives (at least) one value that is characteristic of the rolling force FW that occurs during rolling of the respective section 10 in the rolling stand 3. The at least one value is measured during the rolling of the respective section 10 in the rolling stand 3 by means of a corresponding detection device 17. For example, the rolling stand 3 can have a pressure cell or the working pressures can be detected in hydraulic actuating devices, whereby the rolling force can be determined in a conventional manner in conjunction with the effective working surfaces of the associated pistons. Alternatively or additionally, the control device 11 can receive (at least) one value in step S3 that is characteristic of the rolling moment M that occurs during rolling of this section 10 in the rolling stand 3.Here, too, the at least one value is measured during the rolling of the respective section 10 in the rolling stand 3 using a corresponding detection device 18. For example, the torque of a rolling drive can be measured or determined based on the motor currents. The control device 11 is connected to the detection device 17 and / or the detection device 18 to receive the measured values. In FIG. 1, this is shown only for the second rolling stand 3. However, a corresponding detection device 17 can be present for each rolling stand 3.

[0073] The following explains only the procedure for the rolling force FW. The same procedure applies to the rolling moment M.

[0074] In a step S4, the control device 11 forms a pair of values ​​from the temperature change ÖT of the respective section 10 and the associated rolling force FW.

[0075] In a step S5, the control device 11 checks whether steps S1 to S4 have been carried out often enough, i.e. whether a sufficient number of value pairs are available. As long as this is not the case, the control device 11 goes directly back to step S1. Otherwise, the control device 11 goes to a step S6. In step S6, the control device 11 determines a gradient G of the rolling force FW relative to the temperature T. In a step S7, the control device 11 checks whether the gradient G is greater than 0. If this is the case, the control device 11 detects in a step S8 that a phase transformation from an austenitic to a ferritic structure occurs during the rolling of the sections 10 of the strip 2 in the rolling stand 3 under consideration.Otherwise, the control device 11 detects in a step S9 that no phase transformation from an austenitic to a ferritic structure occurs during the rolling of the sections 10 of the strip 2 in the rolling stand 3 under consideration, thus the structure is either purely austenitic or purely ferritic. How it can be determined whether the structure is purely austenitic or purely ferritic will be explained below.

[0076] In a final step S10, the control device 11 checks whether the rolling of the strip 2 is complete. Depending on the result of the check, the control device 11 returns to step S1 or the procedure of FIG. 3 is completed.

[0077] The procedure in FIG 3 is based on the following physical effect, explained below in conjunction with FIG 5: At a high temperature T of the strip 2, rolling initially takes place with an austenitic microstructure (marked by “A” in FIG 5). As the temperature T decreases and other conditions remain unchanged (in particular material of the strip 2, rolling speed, adjustment of the rolling stand 3, thickness of the strip 2 before rolling and pass reduction), the rolling force FW increases. If the temperature falls below an upper limit T1, a phase transformation of the microstructure from austenite to ferrite occurs. This means that there is a mixture of austenite and ferrite (marked by “A+F” in FIG 5). The proportion of ferrite increases as the temperature T decreases. As a result, with other conditions remaining unchanged, the rolling force FW required for rolling decreases despite a reduction in temperature T.The rolling force FW decreases until the phase transformation from austenite to ferrite is complete or at least almost complete at a lower limit temperature T2. Thereafter, the rolling force FW increases again with the temperature T decreasing even further and otherwise unchanged conditions. The corresponding range is marked with “F” in FIG 5. FIG 5 shows a corresponding possible curve of the rolling force FW as a function of temperature T from the fully austenitic to the fully ferritic range. The exact curve depends on many factors, for example the chemical composition of the steel and partly also its pretreatment. However, the systematic curve, i.e. in particular a reversal of the sign of the gradient G in the mixed ferritic / austenitic range, is typical.

[0078] The rolling of the sections 10 in the rolling stand 3 takes place within the scope of the respective rolling pass across the entire strip 2 (i.e. across all of the sections 10) at a substantially constant temperature ?. However, slight fluctuations in the temperature ? occur. Purely as an example, FIG. 5 shows the temperature ranges TB1 to TB4 in which the rolling of the sections 10 of the strip 2 can take place during various rolling passes. With reference to the design of the rolling mill 1 as a multi-stand rolling mill in FIG. 1, for example,

[0079] - in the first rolling stand 3 of the rolling mill 1, rolling of the sections 10 takes place in the temperature range TB1,

[0080] - in the second rolling stand 3 of the rolling mill 1, rolling of the sections 10 takes place in the temperature range TB2,

[0081] - in the penultimate rolling stand 3 of the rolling mill 1, rolling of sections 10 takes place in the temperature range TB3 and

[0082] - in the last rolling stand 3 of the rolling mill 1, rolling of sections 10 takes place in the temperature range TB4.

[0083] FIG. 6 shows, purely as an example, the temperature range TB3 for the penultimate roll stand 3 of rolling mill 1. The small crosses in FIG. 6 each represent a single pair of values, as characterized by the respective temperature change ÖT and the associated rolling force FW. It is clear that a best-fitting straight line and its gradient can be determined—for example, by linear regression. The gradient is the desired gradient G, whereby in this case, the absolute value is less important than the sign of the gradient G.

[0084] As already mentioned, the method of FIG. 3 can be carried out within a sequence of rolling passes for several rolling passes carried out one after the other, for example, in the case of the multi-stand rolling mill of FIG. 1, for each rolling stand 3 of the rolling mill. If the method is carried out for several rolling passes, it is possible to determine, by comparing the gradients G determined for the individual rolling passes, at which of the rolling passes a phase transformation from an austenitic to a ferritic structure occurs for the first time and / or at which of the rolling passes a phase transformation from an austenitic to a ferritic structure occurs for the last time. One possible procedure for such a determination is explained in more detail below in conjunction with FIG. 7.In conjunction with FIG 7, a manner is also explained by means of which, in the event that no phase transformation from an austenitic to a ferritic structure occurs during a rolling pass, it can be decided whether the sections 10 of the strip 2 are rolled austenitically or ferritically in the rolling pass.

[0085] In FIG. 7, n denotes the number of rolling passes. In the multi-stand rolling mill, the number of rolling passes corresponds to the number of rolling stands 3; i and k are indices that select rolling passes. Analogous to FIG. 5, A is used as an abbreviation for austenite, and F is used as an abbreviation for ferrite. According to FIG. 7, the control device 11 initially assumes, in a step S11, that the rolling is austenitic (A) for all rolling passes / rolling stands 3. However, this determination is initially only provisional.

[0086] In a step S12, the control device 11 sets the index k to the value 0. In step S13, the control device 11 increases the index by 1.

[0087] In a step S14, the control device 11 checks whether the index k is greater than the number n of rolling passes. If this is the case, the determination of FIG. 7 is complete. Thus, in a step S15, further measures based on the determination of FIG. 7 can be taken.

[0088] If the check in step S14 shows that the index k is not greater than the number n of rolling passes, the control device 11 proceeds to step S16. In step S16, the control device 11 checks whether the gradient G determined for the rolling pass specified by the index k is greater than 0. If this is the case, the control device 11 assumes for all rolling passes from rolling pass k onwards that rolling takes place with a phase transformation, i.e. austenitic and ferritic (A+F). Here, too, the determination for the rolling passes from the k-th rolling pass onwards is initially only provisional. For the rolling passes before the k-th rolling pass, however, the previous determination in step S11 becomes final. Starting from step S17, the control device 11 returns to step S13.

[0089] If the check in step S16 shows that the gradient G is not greater than 0, the control device 11 proceeds to step S18. In step S18, the control device 11 checks whether it has already assumed for the rolling pass determined by the index k that rolling will occur with a phase transformation, i.e. whether it has already made the change from purely austenitic to mixed austenitic-ferritic rolling for this rolling pass in step S17. If this is not the case, the control device 11 returns to step S13. Otherwise, in step S19, the control device 11 assumes for all rolling passes from the kth rolling pass onwards that rolling will be purely ferritic (F). The determination of the type of rolling (purely austenitic, purely ferritic, or mixed) for all rolling passes is now complete and thus final.

[0090] Using the procedure shown in FIG. 7, the control device 11 can determine the rolling pass in the sequence of rolling passes at which a phase transformation from an austenitic to a ferritic structure occurs for the first time. Alternatively or additionally, the control device 11 can determine the rolling pass in the sequence of rolling passes at which a phase transformation from an austenitic to a ferritic structure occurs for the last time. Building on the procedure shown in FIG. 7, the control device 11 can thus determine the corresponding rolling pass in a step S21, for example as shown in FIG. 8. In a step S22, the control device 11 can then check whether the found rolling pass corresponds to a predetermined rolling pass, for example the first rolling pass in the sequence of rolling passes, the third rolling pass in the sequence of rolling passes, or the last rolling pass in the sequence of rolling passes.Depending on the test of step S22, the control device 11 can therefore vary operating parameters of the rolling mill 1 in a step S23, if necessary.

[0091] Varying the operating parameters is possible regardless of whether one and the same rolling stand 3 performs several rolling passes consecutively or whether each rolling stand 3 performs only one rolling pass. In both cases, by varying the operating parameters, it can be achieved that the rolling pass in which a phase transformation from an austenitic to a ferritic structure occurs for the first or last time is a predetermined rolling pass in the sequence of rolling passes.

[0092] Varying the operating parameters of the rolling mill 1 depending on other circumstances is also possible. In particular, naturally always taking into account the rolling stand in which a phase transformation from an austenitic to a ferritic structure occurs for the first time and / or the rolling stand in which a phase transformation from an austenitic to a ferritic structure occurs for the last time, they can be adjusted in such a way that a specified energy consumption of the rolling mill 1 is minimized, a productivity of the rolling mill 1 is maximized, a rolling force FW of at least one of the rolling passes is reduced, and / or a product property of the strip 2 is optimized after the sequence of rolling passes has been completed.

[0093] Finally, according to FIG. 9, it is possible for the control device 11 to check for a specific rolling pass in a step S31 whether the respective rolling pass in the rolling stand 3 is ferritic. If this is the case, the control device 11 can, for example, in a step S32, adapt a model of the rolling of the strip 2 in a manner specific to ferritic rolling. If this is not the case, the control device 11 can check for this rolling pass in a step S33 whether the rolling pass is austenitic. If this is the case, the control device 11 can, for example, in a step S34, adapt a model of the rolling of the strip 2 in a manner specific to austenitic rolling. If, however, neither (purely) ferritic nor (purely) austenitic rolling takes place in the rolling pass under consideration, the rolling model of the strip 2 is not adapted.As a result, the adaptation of the model depends on the decision whether the rolling pass under consideration is ferritic or austenitic.

[0094] The present invention has many advantages. The most important advantage is that—in contrast to prior art procedures—modeling with all its inherent uncertainties is no longer necessary; instead, whether a phase transformation is present or not can be determined based on measured data. Austenitic rolling occurs before the phase transformation, and ferritic rolling follows the phase transformation. Furthermore, the present invention is widely applicable, particularly both for rolling slabs independently of the casting process and for rolling from the casting heat.

[0095] Although the invention has been illustrated and described in detail by the preferred embodiments, the invention is not limited by the disclosed examples and other variations can be derived therefrom by those skilled in the art without departing from the scope of the invention.

[0096] List of reference symbols

[0097] 1 rolling mill

[0098] 2 volumes

[0099] 3 rolling stands

[0100] 4 oven

[0101] 5 Descaling device

[0102] 6 Cooling unit

[0103] 7 Cooling section

[0104] 8 scissors

[0105] 9 reel

[0106] 10 sections

[0107] 11 Control device

[0108] 12 Control program

[0109] 13 Machine code

[0110] 14 Temperature measuring station

[0111] 15 Temperature measuring station

[0112] 16 Facility

[0113] 17, 18 Recording devices

[0114] A Austenite

[0115] F Ferrite

[0116] FW rolling force

[0117] G Gradient

[0118] M rolling moment

[0119] S1 to S34 steps

[0120] T, T, T“ temperatures

[0121] T1, T2 limit temperatures

[0122] TB1 to TB4 temperature ranges

[0123] ÖT temperature change

Claims

Claims 1. Operating method for at least one rolling stand (3) of a rolling mill (1) for rolling a strip (2) of steel, - wherein during the rolling of successively rolled sections (10) of the strip (2) in the rolling stand (3) during a rolling pass, characteristic values ​​for the rolling force (FW) and / or the rolling moment (M) occurring are measured, - wherein, by utilising the rolling forces (FW) and / or rolling torque (M) occurring during rolling of the sections (10) of the strip (2) in the rolling stand (3) and determined by the measured values, and by changes (ÖT) in the associated temperatures (T) of the sections (10) of the strip (2), a gradient (G) of the rolling force (FW) and / or the rolling torque (M) relative to the temperature (T) is determined, and - wherein the gradient (G) is used to determine whether or not a phase transformation from an austenitic to a ferritic structure occurs in the sections (10) of the strip (2) during rolling in the rolling stand (3).

2. Operating method according to claim 1, characterized in that the changes (ÖT) in the temperature (T) of the sections (10) are determined or estimated on the basis of a temperature (T, T") measured before or after the rolling of the sections (10).

3. Operating method according to claim 1 or 2, characterized in that - that it is carried out for several rolling passes carried out one after the other in time within a sequence of rolling passes carried out one after the other by means of the at least one rolling stand (3) of the rolling mill (1), - by comparing the gradients (G) determined for the individual rolling passes, it is determined at which of the rolling passes a phase transformation from an austenitic to a ferritic structure occurs for the first time and / or at which of the rolling passes a phase transformation from an austenitic to a ferritic structure occurs for the last time, and - that operating parameters of the rolling mill (1) are varied depending on which of the rolling passes a phase transformation from an austenitic to a ferritic structure occurs for the first time and / or which of the rolling passes occurs for the last time.

4. Operating method according to claim 3, characterized in that the operating parameters of the rolling mill (1) are adjusted in such a way that the rolling pass in which a phase transformation from an austenitic to a ferritic structure, is a predetermined rolling pass in the sequence of rolling passes.

5. Operating method according to claim 3 or 4, characterized in that the operating parameters of the rolling mill (1) are adjusted in such a way that a specified energy consumption of the rolling mill (1) is minimized, a productivity of the rolling mill (1) is maximized, a rolling force (FW) of at least one of the rolling passes carried out by at least one of the rolling stands (3) is reduced and / or a product property of the strip (2) is optimized after the execution of the sequence of rolling passes.

6. Operating method according to one of the above claims, characterized in that in the case that no phase transformation from an austenitic to a ferritic structure takes place, a decision is made as to whether the sections (10) of the strip (2) in the rolling stand (3) are to be rolled austenitically or ferritically in a respective rolling pass, and that an adaptation of a model of the rolling of the strip (2) is dependent on this decision.

7. Control program for a control device (11) of a rolling mill (1) comprising at least one rolling stand (3) for rolling a strip (2) made of steel, wherein the control program comprises machine code (13) which can be processed by the control device (11), wherein the processing of the machine code (13) by the control device (11) causes the control device (11) - during the rolling of successively rolled sections (10) of the strip (2) in the rolling stand (3), receives, in each rolling pass, measured values ​​characteristic of the rolling force (FW) and / or the rolling moment (M) occurring, - by utilising the rolling forces (FW) and / or rolling moments (M) occurring during rolling of the sections (10) of the strip (2) in the rolling stand (3) determined by the measured values ​​and the changes (ÖT) in the associated temperatures (T) of the sections (10) of the strip (2) known to the control device (11), a gradient (G) of the rolling force (FW) and / or the rolling moment (M) relative to the temperature (T) is determined and - using the gradient (G) to determine whether or not a phase transformation from an austenitic to a ferritic structure occurs in the sections (10) of the strip (2) during rolling in the rolling stand (3).

8. Control program according to claim 7, characterized that the processing of the machine code (13) by the control device (11) causes the control device (11) to determine or estimate the changes (ÖT) in the temperature (T) of the sections (10) on the basis of a temperature (T, T") measured before or after the rolling of the sections (10).

9. Control program according to claim 7 or 8, characterized in that the processing of the machine code (13) by the control device (11) causes the control device (11) - the gradient (G) of the rolling force (FW) relative to the temperature (T) within a sequence of rolling passes carried out successively by means of the at least one rolling stand (3) of the rolling mill (1) is determined for a plurality of rolling passes carried out successively in time, - by comparing the gradients (G) determined for the individual rolling passes, it is determined at which of the rolling passes a phase transformation from an austenitic to a ferritic structure occurs for the first time and / or at which of the rolling passes a phase transformation from an austenitic to a ferritic structure occurs for the last time, and - Operating parameters of the rolling mill (1) vary depending on which of the rolling passes a phase transformation from an austenitic to a ferritic structure occurs for the first time and / or which of the rolling passes occurs for the last time.

10. Control program according to claim 9, characterized in that the processing of the machine code (13) by the control device (11) causes the control device (11) to adjust the operating parameters of the rolling mill (1) in such a way that the rolling pass in which a phase transformation from an austenitic to a ferritic structure occurs for the first time or for the last time is a predetermined rolling pass in the sequence of rolling passes.

11. Control program according to claim 9 or 10, characterized in that the processing of the machine code (13) by the control device (11) causes the control device (11) to adjust the operating parameters of the rolling mill (1) in such a way that a specified energy consumption of the rolling mill (1) is minimized, a productivity of the rolling mill (1) is maximized, a rolling force (FW) of at least one of the rolling passes carried out by at least one of the rolling stands (3) is reduced and / or a product property of the strip (2) is optimized after the execution of the sequence of rolling passes.

12. Control program according to one of claims 7 to 11, characterized that the processing of the machine code (13) by the control device (11) causes the control device (11) to decide, in the event that no phase transformation from an austenitic to a ferritic structure takes place, whether the sections (10) of the strip (2) in the rolling stand (3) are to be rolled austenitically or ferritically in a respective rolling pass, and that the control device (11) adapts a model of the rolling of the strip (2) depending on this decision.

13. Control device of a rolling mill (1) for rolling a strip (2) of steel, wherein the control device is programmed with a control program (12) according to one of claims 7 to 12, so that the control device carries out an operating method according to one of claims 1 to 6 during operation.

14. Rolling mill for rolling a strip (2) made of steel, - wherein the rolling mill comprises at least one rolling stand (3) in which sections (10) of the strip (2) are rolled one after the other, - wherein the rolling stand (3) is assigned a detection device (17, 18) for measuring values ​​which are characteristic of the rolling force (FW) occurring during rolling of the sections (10) of the strip (2) and / or the rolling moment (M) occurring during rolling of the sections of the strip, - wherein the rolling mill has a control device (11) controlling the rolling stand (3), - that the control device (11) is connected to the detection device (17, 18) for receiving the measured values ​​and - wherein the control device (11) is designed as a control device according to claim 13.

15. Rolling mill according to claim 14, characterized in that the control device (11) is data-technically connected to a device (16) for specifying the temperatures (T) of the sections (10) of the strip (2) or their changes (ÖT) and / or is data-technically connected to a temperature measuring station (14, 15) arranged upstream or downstream of the rolling stand (3) for measuring the temperature (T, T") of the sections (2).

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