CN114173957A

CN114173957A - Production of deep-drawable steel strip in a combined casting and rolling installation

Info

Publication number: CN114173957A
Application number: CN202080053420.XA
Authority: CN
Inventors: S·布拉金; S·格罗塞博; T·伦高尔; B·林泽尔; A·利穆纳克
Original assignee: Primetals Technologies Austria GmbH
Current assignee: Primetals Technologies Austria GmbH
Priority date: 2019-07-24
Filing date: 2020-07-01
Publication date: 2022-03-11
Anticipated expiration: 2040-07-01
Also published as: EP4003623A1; CN114173957B; EP3769862A1; WO2021013488A1

Abstract

The invention relates to a method for producing a product strip (6) from steel in a cast-rolling composite plant (1) and to a cast-rolling composite plant (1) suitable for this purpose. The aim of the invention is to provide a method by which a thin finished strip (6) having good deep drawability and high surface quality can be produced directly on a cast-rolling mill complex without the need for pickling and cold rolling of the finished strip (6) after hot rolling. This object is achieved by a method according to claim 1.

Description

Production of deep-drawable steel strip in a combined casting and rolling installation

Technical Field

The invention relates to the technical field of metallurgy. In one aspect, the invention relates to a method for producing a deep-drawable finished strip from steel by continuous casting and hot rolling in a combined casting and rolling plant. In another aspect, the present invention relates to a cast rolling complex apparatus suitable therefor.

Casting and rolling complex plants, such as, for example, an Arvedi ESP plant, an SMS CSP plant or a Danieli QSP plant, are known in principle to the person skilled in the art. It is also known that thin or ultra-thin strips of various steel qualities can be produced in a casting and rolling complex in a particularly energy-efficient manner.

Background

Since steel strips often have to have a certain degree of deep drawability, which according to the prior art could not be achieved by conventional hot rolling, the microstructure of the finished strip, which is necessary for the deep drawability, is adjusted by hot rolling in a conventional hot rolling train or a combined casting and rolling installation, pickling and subsequent cold rolling with a high degree of deformation and annealing. The annealed strip is often subsequently also galvanized.

Although it is possible to produce steel strips with a thickness of <1mm directly (i.e. without cold rolling) on a cast-rolling complex, the advantages of the cast-rolling complex are partially lost again by the subsequent pickling-cold-rolling-annealing and, if necessary, galvanizing steps. Therefore, there is a need for: thin steel strips with good deep drawability and high surface quality are produced directly on a cast-rolling complex without the need for subsequent pickling, cold rolling and annealing of the strip.

A cast-rolling compound plant and a method for producing a finished strip from steel are known from CN 207288354U, said cast-rolling compound plant having:

a continuous casting installation 1 with curved strand guiding devices,

a roughing train 2 for roughing the roughing belt,

an intensive cooling device 4 for intensive cooling of the rough rolled strip, whereby the austenite in the rough rolled strip is at least partially converted into ferrite,

a descaling device 6 for descaling the intensively cooled rough rolled strip,

a multi-stand finishing train 8 with a roll gap lubrication for finishing the descaled rough rolled strip into a finished strip; and

two winding devices 11 for winding the finished strip.

A disadvantage of the plant of CN 207288354U is that the surface quality of the finished strip produced is not optimal, since the rough rolled strip is first subjected to intensive cooling and subsequently descaled before finish rolling without intermediate heating. Because the descaling is carried out after intensive cooling and thus already at relatively low temperatures, it is not thorough enough for the high requirements with regard to the surface quality. Thus, in the case of a finished hot-rolled strip, which requires high surface quality, at least pickling and cold rolling must be carried out.

Disclosure of Invention

The object of the present invention is to modify the known method for producing thin strip from steel in such a way that a thin finished strip with good deep drawability and high surface quality can be produced directly on a cast-rolling mill complex without the need for pickling and cold rolling of the finished strip after hot rolling. According to a further aspect of the invention, a cast-rolling complex should be found which is particularly well suited to this.

The method aspect of the object is solved by a method according to claim 1. Advantageous embodiments are the subject of the dependent claims.

In particular, the solution is achieved by a method for producing a finished strip from steel in a cast-rolling composite plant, comprising the following method steps:

-continuously casting a liquid steel in a continuous casting plant into a cast strand having a slab cross section or a sheet slab cross section, wherein the liquid steel comprises C <0.01% (preferably C < 0.004%), Mn <0.2%, P <0.01%, optionally Ti + Nb > 0.01%; the remainder comprising Fe and possible impurities (also called accompanying elements);

rough rolling an uncut cast slab in a roughing train to form a rough rolled strip, wherein the last rolling pass in the roughing train is carried out in the austenite range and the thickness of the cast slab is reduced by at least 30%, preferably by at least 60%, particularly preferably by at least 80%, by rough rolling;

-heating, preferably induction heating, the rough rolled strip to a surface temperature >1000 ℃, preferably >1050 ℃, particularly preferably ≥ 1080 ℃; followed by

-descaling and intensive cooling of the descaled raw strip by means of a liquid coolant, so that the austenite in the raw strip is at least partially, preferably completely, converted into ferrite;

-finishing an uncut, at least partially, preferably completely, rough rolled strip of ferritic body in a finishing train through a plurality of rolling passes into a finished strip, wherein the finished strip has a thickness after the last rolling pass of between 0.5 and 4mm, preferably between 0.6 and 2 mm;

-roll gap lubrication is carried out in the last rolling pass, preferably in a plurality of the last rolling passes, particularly preferably in all the rolling passes, in the finishing train, thereby reducing the friction between the working rolls and the rolled stock of the finishing stand, thus preventing shearing in the finished strip, which leads to the development of undesired goss texture;

-winding the finished strip in the winding device, wherein the ferrite in the finished strip at least partially constitutes a {111} texture.

The combined casting and rolling installation for carrying out the method according to the invention comprises at least one continuous casting installation for continuously casting a cast strand, a roughing mill train (roughing mill, english) for roughing the cast strand into a roughing strip, a finishing mill train (finishing mill, english) having a plurality of finishing mill stands for finishing the roughing strip into a finished strip, and at least two winding devices for winding up the finished strip. The roughing train is constructed in a single-stand or multi-stand configuration.

In the cast-rolling complex plant, a liquid steel is first continuously cast in a continuous casting plant into a cast strand having a slab cross section or a sheet bar cross section, wherein the liquid steel contains C <0.01% (preferably C < 0.004%), Mn <0.2%, P <0.01%, preferably Ti + Nb > 0.01%, and the remainder contains Fe and possibly impurities or other accompanying elements (percentages indicate wt.%, in each case). The continuous cast strand is subsequently rolled in a roughing train to form a roughing strip, the last rolling pass in the roughing train being carried out in the austenitic range and the thickness of the cast strand being reduced by roughing by at least 30%, preferably by at least 60%, particularly preferably by at least 80%. Immediately after the rough rolling, the austenite in the rough rolled strip is at least partially transformed into ferrite, so that the rough rolled strip enters the finishing train in a completely ferritic or partially ferritic state. The rough rolled strip is first heated, preferably inductively, to a surface temperature of more than 1000 ℃, then descaled and finally subjected to intensive cooling by means of a liquid coolant, whereby the austenite in the rough rolled strip is at least partially, preferably completely, converted into ferrite. In order to obtain a high surface quality, it is advantageous to heat the rough rolled strip to a surface temperature >1050, preferably ≧ 1080 ℃. As a result, the descaling can be carried out particularly thoroughly, so that the finished belt has a high surface quality. In order to avoid local melting of the rough-rolled strip or of the oxide layer covering the rough-rolled strip, the maximum surface temperature of the rough-rolled strip is limited when heating at 1200 ℃. In the finishing train, a continuous strand of the at least partially transformed rough strip is hot-rolled in a plurality of rolling passes to form a finished strip, wherein the finished strip has a thickness of between 0.5 and 4mm, preferably between 0.6 and 2mm, after the last rolling pass. In order to prevent shear strips from forming in the finished strip, which lead to the development of undesirable goss texture, roll gap lubrication is used in the finish rolling in the last rolling pass, preferably in a plurality of the final rolling passes (for example in the last and second to last rolling passes), particularly preferably in all rolling passes, wherein the roll gaps are lubricated in each case, for example, by a liquid lubricant, such as oil or mineral oil. After the finish rolling, the finished strip is laterally separated and wound in one of at least two winding devices, wherein the ferrite in the finished strip at least partially forms a {111} texture. By means of the transverse separation of the finished strip, the continuous product is first subjected to a transverse separation after the finish rolling (and most of all after the cooling section typically present) so that the coil or bundle has a specific weight or a specific length. The so-called 111 texture of the ferrite is responsible for the good deep drawability of the finished strip. In principle, the more ferrite with a {111} texture present in the finished strip, the better the deep drawability. If the liquid steel contains Ti and/or Nb, wherein the sum of these alloying elements Ti + Nb is 0.01% or more, the finished strip has improved deep drawability again, since the finished strip of ferritic-rolled, titanium-alloyed and/or niobium-alloyed steel has a higher proportion of ferrite with a {111} texture. For secondary requirements, the addition of Ti and/or Nb can be dispensed with in many cases.

The continuous operation in the cast-rolling complex ensures optimum process stability and thus uniform strip geometry and mechanical properties.

In order to reduce the frictional stresses in the roll gap, it is advantageous if the roll gap has a low ratio of the extruded length to the average roll gap height. This is achieved by: in the finishing train, the diameter of the working rolls in the last rolling pass, preferably in a plurality of rolling passes in the last rolling pass, particularly preferably in all rolling passes, is between 200mm and 750mm, preferably between 200mm and 500 mm.

Alternatively or additionally, in order to reduce the frictional stresses in the roll gap, it is advantageous if, in the finishing train, the coefficient of friction μ between the working rolls and the rolling stock in the last rolling pass, preferably in a plurality of rolling passes in the last rolling pass, particularly preferably in all rolling passes, is μ ≦ 0.15. This can be achieved by roll gap lubrication and/or by a particularly smooth surface of the work rolls. According to the invention, a roll gap lubrication device is provided, since otherwise the friction coefficient μ ≦ 0.15 cannot be ensured in longer rolling movements with a rolling length greater than 150 km.

The degree of deformation of the first rolling pass in the finishing train is typically greater than that of the last rolling pass, or all rolling passes have a decreasing trend of the degree of deformation, i.e. the degree of deformation of the earlier rolling pass is greater than that of the later rolling pass.

In order to form a high proportion of ferrite with {111} texture, it is advantageous if the total degree of deformation of all rolling passes in the finishing train is equal to or greater than 70%.

There are two possible solutions for the temperature control in the cast rolling complex. According to option 1, the temperature of the rough-rolled strip at the exit from the roughing train is greater than or equal to 900 ℃, the temperature of the finished strip at the exit from the finishing train is between 700 and 800 ℃, and the coiling temperature is greater than 680 ℃. The coiling temperature can also be 670 ℃ or more for a particular steel quality. In the case of ferritic rolling, it is advantageous if the distance between the last stand of the finishing train and the coiler is small, since the temperature drop is thereby kept low. Alternatively or additionally, it is advantageous to reduce the temperature drop of the finished strip between the last stand of the finishing train and the coiler by means of heat-insulating plates. Preferably, the insulation panels are constructed to be installed in the cooling stage or to be detachable so that they are used only when ferrite rolling is performed. According to option 2, the temperature of the rough-rolled strip at the exit from the roughing train is greater than or equal to 900 ℃, the temperature of the finished strip at the exit from the finishing train is less than 750 ℃, and the coiling temperature is less than 600 ℃.

When using option 2, it is advantageous to subject the finished tape to a recrystallization anneal after winding. Grain reconstruction of the ferrite structure occurs by the recrystallization annealing. Option 1 is advantageous in that no recrystallization anneal is required.

According to the invention, after heating, the rough-rolled strip is first descaled and then subjected to intensive Cooling by means of a liquid coolant (for example by means of the so-called "Power Cooling" from Primels Technologies). Because the rough-rolled strip is first descaled and only thereafter subjected to intensive cooling, the descaling is performed at a relatively high surface temperature, which causes thorough descaling. This sequence contributes significantly to achieving a high surface quality of the finished strip, especially for deep-drawing quality. It is known from the prior art to carry out cooling before descaling, which sequence is disadvantageous for the deep drawing quality due to the poor surface quality.

It is not critical for the desired {111} texture to be present in the finished strip to de-scale the strip before or after cooling.

In one embodiment, either the cast strand or the rough-rolled strip is covered with a scale-inhibiting powder, so that the rough-rolled strip, after active or passive cooling, enters the finishing train in the form of fully ferritic or partially ferritic. In such an embodiment, it is possible even to dispense with descaling and in most cases to dispense with heating of the rough-rolled strip. The powder can be, for example, a borate, in particular a salt of boric acid, particularly preferably a sodium salt of boric acid, very particularly preferably borax with or without crystal water, such as anhydrous borax (Na)₂B₄O₇) Borax pentahydrate (Na)₂B₄O₇·5H₂O) or borax decahydrate (Na)₂B₄O₇·10H₂O), or the powder comprises at least one of these compounds.

For a specific temperature control, it may be necessary to reduce the temperature drop of the finished strip between the last stand of the finishing train and the coiler by means of heat-insulating plates. In other words, the finished belt is insulated at the designated locations. By this means, the finishing temperature in the finishing train can be kept low and the coiling temperature can be kept relatively high.

The object is also achieved by a combined casting and rolling plant according to claim 12, wherein the combined casting and rolling plant has:

a continuous casting system with curved strand guides for continuously casting a strand with a slab or thin slab cross section;

-a roughing train for roughing the cast slab into a roughing strip;

-an induction furnace for heating the raw rolled strip to a surface temperature >1000 ℃;

-descaling means for descaling the heated rough rolled strip;

-an intensive cooling device for intensive cooling of the descaled raw strip by means of a liquid coolant, whereby austenite in the raw strip is at least partially converted into ferrite;

a finishing train having a plurality of finishing stands for finishing the intensively cooled rough rolled strip into a finished strip, wherein the finished strip has a thickness after the last rolling pass of between 0.5 and 4mm, preferably between 0.6 and 2 mm;

a roll gap lubrication device in the finishing train, which reduces the friction between the working rolls of the finishing stand and the rolled stock to μ ≦ 0.15 in the last rolling pass, preferably in a plurality of, particularly preferably all, of the final rolling passes;

-a shear for transversely separating the finished strip; and

-at least two winding devices for winding the finished strip.

In the case of ferritic rolling, it is advantageous if an insulating plate for insulating the finished strip is arranged between the last stand of the finishing train and the winding device.

In order to precisely regulate the intensive cooling or the transformation of the austenitic structure into the ferritic structure before the finish rolling, a pyrometer for measuring the actual temperature of the rolling stock is advantageously arranged between the first stand and the second stand of the finishing train, said pyrometer being connected to a regulator which can take into account the actual temperature T_IstAnd a target temperature T_SollThe regulating variable is calculated and the regulator can control an actuator (for example, a valve or a water pump) of the intensive cooling device in such a way that the actual temperature T_IstAs far as possible from the target temperature T_SollAnd correspondingly. In principle, the pyrometer can also be arranged upstream of the finishing train or downstream of the first stand of the finishing train. Preferably, however, is arranged between the first and second housings.

The target temperature T is set when ferrite rolling is performed_SollPreference is given to<850 ℃. However, T_SollIn principle depending on the steel quality.

Since the roughing train enters the finishing train by intensive cooling immediately upstream of the finishing train, rather than dry, the temperature measurement is not carried out upstream of the finishing train, as is known in principle in the prior art, but after the first stand. Thereby ensuring a high accuracy of the temperature measurement. By adjusting the intensive cooling, it is ensured that the first rolling pass already takes place in the predetermined phase region during the finish rolling.

Drawings

The above features, characteristics and advantages of the present invention, and the manner and method of how to achieve them, will become more apparent in conjunction with the following description of various embodiments, which are explained in detail in conjunction with the accompanying drawings. Here:

FIG. 1 shows a schematic representation of a casting and rolling complex according to the invention for carrying out the method according to the invention,

figure 2 shows a schematic view of a casting and rolling complex not according to the invention,

figure 3 shows the thickness profile for three variants of the method according to the invention,

figure 4 shows the temperature profile for three variants of the method according to the invention,

fig. 5 shows a variant of the inventive cast-rolling complex for carrying out the inventive method.

Detailed Description

In the combined casting and rolling installation 1 of fig. 1, a liquid steel having the following chemical composition is continuously cast in the continuous casting installation 2 into a cast strand 3 having a slab cross section.

Element(s)	By weight%
		C	＜0.004
Mn	＜0.2
		P	＜0.01
Ti+Nb	0.03
		Fe	The remaining part

Table 1: chemical composition of the steel.

The cast strand 3 leaves the continuous casting installation 2 with a thickness of 110mm and a speed of 6 m/min. Preferably, the partially solidified strand 3 is subjected to a soft or Liquid Core Reduction (LCR) in an arcuate strand guide. Thereby reducing the thickness of the cast slab and improving the internal quality thereof. The cast strand 3 enters the three-stand roughing train 5 uncut and is reduced there to form a roughing strip 4 having a thickness of 10 mm. The last rolling pass in stand R3 of roughing train 5 is carried out at a finishing temperature of 1000 ℃ in the austenitic temperature range. Next, the temperature of the roughly rolled strip 4 is heated to 1080 ℃ by the induction furnace IH, and then cooled to 850 ℃ by the descaling device D and the intensive cooling device 7. In this case, the austenite present in the rough-rolled strip 4 is at least almost completely converted into ferrite. The continuous, phase-changed rough strip 4 is then passed into a five-stand finishing train 8 and is finished there in 5 passes to form a finished strip 6 having a thickness of 1 mm. The last three rolling passes in the rolling stands F3, F4, and F5 of the finishing train 8 are carried out using a roll gap lubrication device. In this case, mineral oil is sprayed between the working rolls and the rolling stock of the finishing stand, which reduces the coefficient of friction in the roll gap to a value of μ < 0.15. This prevents shear bands from forming in the finished strip, which could lead to the formation of undesirable goss textures. The finished strip 6 leaves the finishing train 8 at a surface temperature of 720 ℃. In order to achieve a high coiling temperature, the finished strip is not cooled in the region of the cooling line 9 shown by the dashed lines, but is insulated by a heat-insulating plate 14. In order to be able to distribute the finished strip 6 on a plurality of bundles, it is laterally divided by a shear 10 before winding. The winding temperature was 690 ℃. Shortly before the bundle reaches its target weight, the continuous finished strip is laterally separated by the slitter 10 and continuously wound onto another winding device (not shown in fig. 1), wherein the ferrite in the finished strip 6 at least partially forms a {111} texture.

Fig. 2 shows a non-inventive combined casting and rolling installation 1, in which the roughing stand 4 is introduced into the finishing train 8 in the partially ferritic state without heating in the induction furnace IH, without descaling in the descaler D or without intensive cooling. Descaling of the roughing strip 4 can be dispensed with, since the upper and lower sides of the cast strand 3 are covered with a scale-inhibiting powder (e.g. borax) in the powder feed device 15. Further details regarding the powder or powder feeding device are referred to WO 2019/068444.

Fig. 3 and 4 show three further variants of the operating method for producing a product strip 6 made of steel on a cast-rolling composite plant 1, which are designated as V1 to V3. The variants according to the invention V1 and V2 are implemented on the cast-rolling complex 1 according to fig. 1; the variant V3 not according to the invention is implemented on the cast-rolling complex 1 according to fig. 2.

According to this variant V3, the rough strip 4, which has passed through the deactivated induction furnace IH, is fed directly to the first stand F1 of the finishing train 8 without being heated, without being cooled by the intensive cooling device 7 and without being descaled in the descaling device D. The casting and rolling complex 1 and the operating method V3 of fig. 2 are thereby further simplified.

In the continuous casting installation 3, in variants V1, V2 and V3, respectively, liquid steel having the chemical composition specified in table 1 is cast into a thin slab 3 of 90mm thickness. The thin slab 3 leaves the continuous casting installation 2 at a casting speed of 6m/min and a temperature of 1100 ℃. Since the roughing train 5 follows the continuous casting installation 2, the uncut thin slab also enters the first stand R1 of the roughing train 5 at 1100 ℃ and is roughed in the three stands R1 … R3 of the roughing train 5 to form a rough strip 4 having a thickness of 12.4 mm. The last rolling pass in stand R3 of roughing train 5 is carried out at 1000 ℃ and thus in the austenitic temperature range of the steel. By the rough rolling, the thickness of the cast slab was reduced by 86%.

In variants V1 and V2, the rough-rolled strip 4 is then heated to 1100 ℃ in an induction furnace IH and then descaled in a descaler D. Here, the temperature of the rough-rolled strip 4 drops to 1000 ℃. Subsequently, the roughly rolled strip is subjected to intensive cooling in an intensive cooling device 7, wherein the temperature of the roughly rolled strip 4 is reduced to 900 ℃ or less.

In variant V3, the rough-rolled strip 4 is neither heated in the induction furnace IH nor descaled in the descaler D. It is equally well possible to dispense with the induction furnace IH and the descaling device D. As described above, the scaling of the cast slab or the rough rolled strip can be reduced or prevented by covering with powder. In this case, the process is energy efficient and the finished belt has a high surface quality.

The austenite in the rough-rolled strip 4 is at least partially converted into ferrite by temperature control of the rough-rolled strip 4 after the last rolling pass R3 in the rough-rolled train 5 and before the first rolling pass F1 in the finishing train 8. The at least partially transformed rough strip 4 then passes uncut into the first stand F1 of the finishing train 8.

According to variant V1, the first rolling pass in the first stand F1 of the finishing train 8 is performed at 875 ℃. The last rolling pass in the fifth stand F5 of the finishing train 8 was carried out at a finishing temperature of 735 ℃. The finished strip 6 with a thickness of 1.7mm passes through the cooling section 9 without cooling and is wound on the winding device DC at a winding temperature of 690 ℃. The finished strip is insulated in the region of the cooling line 9 by means of insulating panels 14. However, it is also possible to dispense with the cooling section 9, i.e. to arrange the coiler DC immediately after the last stand F5 of the finishing train 8. However, since different products are usually produced on the cast-rolling complex 1, there is typically a cooling section 9.

In variants V2 and V3, the first rolling pass in the first stand F1 of the finishing train 8 is carried out at 840 ℃. The final rolling pass in the fifth stand F5 was carried out at a finishing temperature of 700 ℃. The finished strip 6 having a thickness of 1.7mm is weakly cooled in the cooling section 9 and wound on the winding device DC at a winding temperature of 550 ℃.

In all three variants, the thickness of the rough strip is reduced by 86% by the finish rolling.

The last three rolling passes in the rolling stands F3, F4, and F5 of the finishing train 8 are again carried out using a roll gap lubrication device.

The average temperatures in the individual units of the cast-rolling complex 1 according to variants V1 to V3 are determined either from fig. 4 or from the following table:

table 2: and (4) controlling the temperature.

The reduction in the stands R1 … R3 and F1 … F5 and the thicknesses of the thin slab 2, the rough-rolled strip 4 and the finished strip 6 according to variants V1 to V3 are derived either from fig. 3 or from the following table:

table 3: thickness and reduction ratio.

In order to ensure continuous operation of the cast rolling plant 1, the finished strip 6 is cut directly before the winding device and is wound alternately by at least two winding devices DC.

By using the method according to the invention in the cast-rolling mill 1, the wound finished strip 6 has good deep drawability without the need for cold rolling or annealing the finished strip 6 after hot rolling. Since the finished tape is wound at relatively low temperatures in variants V2 and V3, no recrystallization takes place in the strand itself. Therefore, the finished tape should be subsequently subjected to a recrystallization anneal. However, even if the finished strip 6 is to be cold-rolled and annealed for higher requirements, the method according to the invention is extremely advantageous, since cold rolling can be carried out with a lower reduction. Good deep drawability results from the chemical composition of the liquid steel on the one hand and from the advantageous use of the method according to the invention on the other hand.

Finally, fig. 5 shows a variant of the inventive cast-rolling plant 1 of fig. 1. In contrast to the apparatus of fig. 1, the intensive cooling device 7 is operated in a temperature-regulated manner. For this purpose, in the finishing train 8Actual surface temperature T after first rack_IstMeasured by a pyrometer or temperature measuring device and transmitted to the regulator C. The regulator C is based on the target surface temperature T_SollAnd the actual surface temperature T_IstTo ascertain the adjustment quantity and to output it to the actuator 13, here a frequency converter. Which governs the rotational speed of the pump 11 via the electric motor 12. Since the pump 11 is a centrifugal pump, the pressure of the liquid coolant sprayed through the nozzles onto the upper and lower sides of the rough-rolled strip (only the nozzles below the rough-rolled strip are shown in fig. 5 for the sake of clarity) varies as a function of the pump speed. Thereby, the cooling degree of the intensive cooling device can be determined according to the measured actual surface temperature T_IstTo adjust. Besides adjusting the rotational speed of the pump, other possibilities of adjusting the degree of cooling are also known to the person skilled in the art, for example by arranging a valve between the pump and one or more nozzles, wherein the flow or pressure of the coolant is adjusted through an opening of the valve. By this measure, it is ensured that the first rolling pass in the finishing train 8 is already carried out in a predetermined phase region of ferrite (typically completely ferrite) even during transient processes in the combined casting and rolling plant 1 (for example, a distributor change with a temporarily reduced casting speed of the continuous casting plant 2). The product properties of the finished wound strip are thereby significantly improved and remain extremely constant. The finished strip 6 is again insulated in the region of the cooling line 9 by means of an insulating plate 14.

For reasons of clarity, only a single winding device DC is shown in each of fig. 1, 2 and 5. However, at least two winding devices are required for a longer rolling movement in order to be able to wind the continuously produced finished strip 6.

Although the invention has been illustrated and described in detail by means of preferred embodiments, it is not limited by the disclosed examples and other variants can be derived therefrom by the person skilled in the art without departing from the scope of protection of the invention.

List of reference numerals:

1 casting and rolling compound equipment

2. CCM continuous casting equipment

3 casting blank

4 rough rolling strip

5 roughing train

6 finished product belt

7 intensified cooling device

8 finishing mill line

9 cooling section

10 shearing machine

11 Pump

12 electric motor

13 actuator

14 heat insulating plate

15 powder feeding device

C regulator

D descaling device

DC winding device

First to fifth stands of F1 … F5 finishing train

IH induction furnace

Inlet of In unit

Out unit outlet

First to third stands of R1 … R3 roughing train

T_IstActual surface temperature

T_SollA target surface temperature.

Claims

1. Method for producing a product strip (6) from steel in a cast-rolling composite plant (1), comprising the following method steps:

-continuously casting a liquid steel in a continuous casting plant (2) into a cast strand (3) having a slab cross section or a thin slab cross section, wherein the liquid steel comprises in weight% C <0.01%, Mn <0.2%, P <0.01%, optionally Ti + Nb ≧ 0.01%, the remainder comprising Fe and possible impurities;

-roughing an uncut cast slab (3) into a roughing strip (4) in a roughing train (5), wherein the last rolling pass (R3) in the roughing train (5) is carried out in the austenitic temperature range and the thickness of the cast slab (3) is reduced by at least 30%, preferably at least 60%, particularly preferably at least 80%, by roughing;

-heating, preferably induction heating, the rough rolled strip (4) to a surface temperature >1000 ℃, preferably >1050 ℃, particularly preferably ≥ 1080 ℃; followed by

-descaling and intensive cooling of the descaled raw strip (4) by means of a liquid coolant, whereby the austenite in the raw strip (4) is at least partially, preferably completely, converted into ferrite;

-finish rolling an uncut at least partially, preferably completely, rough rolled strip (4) of ferritic body into a finished strip (6) in a finishing train (8) in a plurality of rolling passes, wherein the finished strip (6) has a thickness after the last rolling pass (F5) of between 0.5 and 4mm, preferably between 0.6 and 2 mm;

-roll gap lubrication is carried out in the last rolling pass (F5), preferably in a plurality of the last rolling passes (F3 … F5), particularly preferably in all the rolling passes (F1 … F5), in the finishing train (8), whereby the friction between the work rolls and the rolled stock of the finishing stand is reduced;

-winding said finished strip (6) in a winding Device (DC).

2. Method according to claim 1, characterized in that the diameter of the working rolls in the last rolling pass, preferably in a plurality of rolling passes of the last rolling pass, particularly preferably in all rolling passes, in the finishing train is between 200mm and 750mm, preferably between 200mm and 500 mm.

3. Method according to claim 1 or 2, characterized in that the coefficient of friction μ between the working rolls and the rolled stock in the last rolling pass, preferably in a plurality of rolling passes in the last rolling pass, particularly preferably in all rolling passes, in the finishing train (8) is μ ≦ 0.15.

4. Method according to any one of claims 1 to 3, characterized in that the degree of deformation of the first rolling pass is greater than the degree of deformation of the last rolling pass in the finishing train (8).

5. Method according to any one of claims 1 to 4, characterized in that the total degree of deformation of all rolling passes in the finishing train (8) is ≥ 70%.

6. The method according to any one of claims 1 to 5, characterised in that the temperature of the roughing belt (4) at the exit from the roughing train (5) is greater than or equal to 900 ℃, the temperature of the finished belt (6) at the exit from the finishing train (8) is between 700 and 800 ℃ and the coiling temperature is greater than 680 ℃.

7. The method according to any one of claims 1 to 5, characterized in that the temperature of the roughing strip (4) upon exiting the roughing train (5) is > 900 ℃, the temperature of the finished strip (6) upon exiting the finishing train (8) is <750 ℃, and the coiling temperature is <600 ℃.

8. Method according to claim 7, characterized in that the final strip (6) is subjected to a recrystallization annealing after winding.

9. Method according to any one of the preceding claims, characterized in that the actual temperature (T) of the product is measured after the first stand (F1) of the finishing train (8)_Ist) The actual temperature (T)_Ist) Is fed to a regulator (C) which takes into account the actual temperature (T)_Ist) And target temperature (T)_Soll) Calculates an adjustment quantity, sends the adjustment quantity to an actuator (13), and the actuator (13) actuates the intensive cooling means (7) in such a way that the actual temperature (T) is_Ist) As far as possible with said target temperature (T)_Soll) And correspondingly.

10. The method of claim 9, wherein the target temperature is <850 ℃.

11. Method according to any one of claims 1 to 10, characterized in that either the cast strand (3) or the rough-rolled strip (4) is covered with a scale-inhibiting covering powder and that the rough-rolled strip (4) is introduced into the finishing train (8) in the state of fully ferritic or partially ferritic after active or passive cooling.

12. Casting and rolling composite plant (1) for producing a product strip (6) made of steel according to any one of the preceding claims, having:

-a continuous casting installation (2) with curved strand guiding devices for continuously casting a strand (3) with a slab or sheet slab cross section;

-a roughing train (5) for roughing the cast slab (3) into a roughing strip (4);

-an induction furnace (IH) for heating the raw rolled strip (4) to a surface temperature >1000 ℃;

-descaling means (D) for descaling the heated roughing strip (4);

-an intensive cooling device (7) for intensive cooling of the descaled raw strip (4) by means of a liquid coolant, whereby austenite in the raw strip (4) is at least partially converted into ferrite;

-a finishing train (8) having a plurality of finishing stands (F1 … F5) for finishing the intensively cooled rough strip (4) to a finished strip (6), wherein the finished strip (6) has a thickness after the last rolling pass (F5) of between 0.5 and 4mm, preferably between 0.6 and 2 mm;

-a roll gap lubrication device in the finishing train (8), which in the last rolling pass (F5), preferably in a plurality of rolling passes in the last rolling pass (F3 … F5), particularly preferably in all rolling passes (F1 … F5), thereby reducing the friction between the working rolls and the rolled stock of the finishing stand to μ ≦ 0.15;

-a shear (10) for transversely separating the finished strip; and

-at least two winding Devices (DC) for winding the finished strip (6).

13. Cast rolling compound plant (1) according to claim 12, characterised in that between the last stand (F5) of the finishing train (8) and the first winding Device (DC) there is arranged a heat insulating plate (14) for heat insulation of the finished strip.

14. Casting and rolling complex (1) according to claim 12 or 13, characterized in that between the first stand (F1) and the second stand (F2) of the finishing train (8) there is arranged an actual temperature (T) for the rolled product_Ist) A pyrometer for taking measurements, said pyrometer being connected to a regulator (C) capable of taking into account said actual temperature (T)_Ist) And target temperature (T)_Soll) And the controller (C) can control an actuator (12) of the intensive cooling device (7) in such a way that the actual temperature (T) is adjusted_Ist) As far as possible from the target temperature (T)_Soll) And correspondingly.