EP1113888A1

EP1113888A1 - Method and device for producing a hot-rolled steel strip from molten steel

Info

Publication number: EP1113888A1
Application number: EP99927572A
Authority: EP
Inventors: Andreas Flick; Clifford Job; Gernot Lettmayr; Olaf Silbermann; Josef Watzinger; Josef LANSCHÜTZER; Franz Wimmer; Josef Maierl; Gerlinde Djumlija; Heinrich THÖNE
Original assignee: Voest Alpine Industrienlagenbau GmbH
Current assignee: Primetals Technologies Austria GmbH
Priority date: 1998-08-17
Filing date: 1999-06-21
Publication date: 2001-07-11
Anticipated expiration: 2019-06-21
Also published as: WO2000010741A1; ATA140198A; DE59902292D1; AT409227B; EP1113888B1

Abstract

The invention relates to a method and a device for producing hot-rolled steel strip. To be able to use said device in a combination plant and with a minimum number of rolling passes the method provides for the following combination of steps: continuous casting of steel melt in a cooled, oscillating continuous-casting mould using the free jet casting method, the pouring stream being protected against atmospheric influences; release of an at least partly solidified casting strand with a strand thickness of between 15 and 50 mm from the continuous-casting mould; possible heating of the casting strand to rolling temperature in a heating phase immediately prior to rolling; rolling of the casting strand to a hot-rolled steel strip having a thickness of between 0.6 and 12.0 mm in several rolling passes; and cooling of the steel strip in a cooling line positioned downstream, followed by coiling of the strip in a reeling plant.

Description

Process and plant for producing hot-rolled steel strip from a molten steel

The invention relates to a method and a plant for the production of hot-rolled steel strip from a molten steel using a single or multi-stand continuous casting plant and its downstream rolling devices.

Direct composite systems for direct rolling of thin slabs, which are formed from a casting plant and a rolling plant, allow a reduction in production costs by utilizing the casting heat and thus minimizing the amounts of energy required for reheating. Furthermore, the production capacity of the rolling mill is fully utilized by maximizing the continuous casting capacity, for example by B. Two-strand casting machines are used. The economic limit of such systems is already today with production quantities of more than 2 million t / year and a corresponding investment is increasingly unrealistic due to the lack of sales markets. The trend towards the production of close-to-size strips, which started with the development of direct-bond systems, continues with the aim of producing thin hot strips in a thickness range and with a quality standard that can be used as a cold strip substitute on the markets. With a final hot strip thickness of 0.6 to 12.0 mm and a correspondingly inexpensive system design, it is possible in this way to economically produce small production quantities of 0.8 to 1.2 million tons / year.

From DE 195 20 832 AI a method and a device for producing steel strip with cold rolling properties is already known, a cast strand having an outlet thickness of 30-100 mm being conveyed out of the continuous casting mold and in three subsequent deformation steps, namely a deformation with the core still liquid is rolled out by at least 10%, a subsequent rolling with a thickness reduction of at least 50% in a three-stand rolling mill and a final isothermal roll in a likewise at least three-stand finishing train, to a finished strip of a maximum of 2 mm thickness. A major disadvantage of this known solution lies in the large number of forming frames for the forming of the cast strand with the core still liquid and the subsequent large number of roll stands to achieve the desired strip target thickness. Furthermore, high demands are placed on the temperature control in the strip, which goes beyond the problem of increased heat loss with thinner hot strip. From DE 195 20 832 AI there are no indications as to how the mold must be designed in order to cast strands in a thickness range of 30-100 mm. Usually, funnel molds with a central extension area on the input side for receiving the immersion pouring tube are used, as are known, for example, from DE 41 35 214 AI. A casting thickness range of 40-80 mm is specified for this proposed funnel mold, with the achievement of casting thicknesses below 50 mm currently not being realistic with this technology. A disadvantage of these funnel molds, however, has been the inevitably necessary deformation of the thin strand shell just formed within the mold, as a result of which folds of the strand shell can occur and there is an increased risk of cracking on the strand surface and just below this surface.

Also known from EP 0 541 574 B1 is a method and a plant for producing a finished strip with cold rolling properties, this strip being produced directly in a hot rolling mill from a starting material produced by continuous casting. The cast thin slab strand leaves the continuous casting mold with a maximum thickness of 100 mm. No information is given on the minimum possible casting thickness. In order to achieve the desired finished strip with cold rolling properties with a strip thickness of less than 1.0 mm, it is necessary to reduce the thickness of the cast strand with a still liquid core in a first deformation step, then the intermediate strip in two further hot forming steps in multi-stand mills and one subsequent cold rolling at a temperature below the transition point Ar ₃ to roll. This process has the defect that many roll stands and roll passes are necessary in order to achieve the desired strip target thickness and thus a complex temperature control is also necessary.

The object of the invention is therefore to avoid these disadvantages and to propose a method and a system for producing hot-rolled steel strip from a molten steel, with which it is possible to achieve a hot strip with a minimum of rolling passes and roll stands, and with a minimum of temperature control measures to come with a low strip target thickness. Another object of the invention consists in the fact that the installation costs of such a plant are drastically reduced by reducing the number of units, in particular the rolling stands and the associated auxiliary units. Another object of the invention is to increase the quality of the product produced, in particular to avoid the occurrence of surface defects on the cast strand.

This task is solved by a procedure consisting of the following chronologically successive steps:

Continuous introduction of a molten steel into a cooled, oscillating continuous casting mold according to the free jet casting process, the pouring jet being shielded from atmospheric influences,

Conveying an at least partially solidified cast strand from the continuous casting mold with a strand thickness of 15 to 50 mm,

If necessary, heating the cast strand to the rolling temperature in a heating stage immediately before rolling the cast strand,

Roll forming of the cast strand into a hot-rolled steel strip with a final strip thickness of 0.6 to 12.0 mm in several roll passes,

• Cooling the steel strip in a downstream cooling section and reeling the strip in the coiler.

By using the free jet casting method proposed according to the invention, it is possible to convey an at least partially solidified cast strand with a strand thickness of 15 to 50 mm, the thin strand shell of which during its formation phase in the continuous casting mold is not subject to any harmful deformations forced by the shape of the mold inner walls, as is the case with continuous casting molds the case is if a funnel-shaped expansion space is provided for the immersion pouring tube protruding into the continuous casting mold on the input side and this extension is traced back inside the continuous casting mold or in the continuous casting mold and the subsequent strand guide to the warm thickness dimension of the cast strand, which is set outside the extension area.

The free jet casting process is a type of introduction of melt into the mold cavity of a continuous casting mold, in which the one from an outlet opening The pouring jet emerging from the melt container is protected from oxidizing influences ^"of the surrounding atmosphere by an insulating chamber with a protective gas atmosphere and without being guided through an immersion pouring tube in free fall into the melt contained in the continuous casting mold and forming a casting level. This immersion casting process is known, for example, from US Pat. No. 3,833,050. US-A 3,840,062 and JP-A 48-9251 are already known and described in detail there, but these applications are limited to the casting of strands with square, rectangular, polygonal or round billet cross sections.

By casting a cast strand with a strand thickness of 15 to 50 mm without harmful strand shell deformation in the continuous casting mold, the outstanding feature of which is the high surface quality and freedom from cracks, it is possible to deflect the casting strand with a small bending radius in the casting system into the horizontal and to carry out a hot deformation. the desired final strip thickness of 0.6 to 12.0 mm is achieved with just a few passes.

Following the roll forming of the cast strand into a steel strip, the strip passes through a cooling section and is wound into a bundle on a strip reel. Depending on the strip thickness and steel quality, the cooling section offers the option of running specific cooling programs in order to set the desired microstructure and material properties.

A particularly favorable application with regard to investment costs and strip quality results if the at least partially solidified cast strand is fed out with a strand thickness of 20 to 40 mm.

The cast strand is rolled into a steel strip in at least one rolling step. In this case, the rolling step is to be understood as the immediately successive sequence of several rolling passes.

An advantageous embodiment of this roll forming in two rolling stages is characterized in that a first roll forming of the cast strand into a preliminary strip takes place in a first rolling stage with a degree of deformation of 10 to 75% and that a further, second rolling forming into a steel strip takes place immediately in a second rolling stage in the Connection to a case-by-case heating of the pre-strip to the rolling temperature. The low casting thickness that can be achieved by free jet casting enables the cast strand to solidify quickly and thus a high casting speed. This results in improved

Conditions for the first roll forming and a reduction in the heat output which is inevitably increased in the case of thin strips, so that under optimal operating conditions it is sufficient to pass the pre-strip through a heating stage immediately before the second roll forming, if this is necessary at all. However, heating the pre-strip immediately before the second roll forming does not preclude that between the two

Treatment steps a descaling of the pre-strip takes place, like this for

Avoiding scaling is common.

In order to enable the second roll shaping of the pre-strip at the rolling speeds customary for a finishing section or a reversing roll stand, it is advantageous that the pre-strip formed by the first roll forming of the cast strand is cut to length according to predetermined coil weights before the second roll forming, if necessary before heating to the rolling temperature. According to an advantageous embodiment of the invention, the cut-to-length pre-strip is wound into a bundle in an intermediate storage station, optionally stored and then unwound again, heated to the rolling temperature and fed to the second rolling deformation. By winding the pre-strip into a bundle immediately after the cutting to length, the length of the composite system and the heat dissipation of the pre-strip to the environment are minimized and the necessary capacity of the heating stage necessary for performing the second roll forming is kept low. When producing pre-strips on continuous casting machines arranged next to one another, which are fed to a common second rolling device, the heat-insulated storage of the pre-strips in an intermediate storage station is absolutely necessary.

An alternative embodiment, in which the pre-strip is heated in the intermediate storage station, is characterized in that the cut-to-length pre-strip is wound into a bundle in an intermediate storage station, optionally stored, heated to the rolling temperature, unwound and fed to the second roll forming.

The investment costs are minimized if the second roll forming is carried out by reversing rolls. In continuous rolling, the steel strip produced by roll forming is cut to length in the cooling section (23) according to predetermined coil weights.

Optimal conditions for the roll deformation result when the casting speed is set to 3 to 12 m / min. The high values of the casting speed are made possible by the rapid solidification of the cast strand at a low casting thickness and are further improved by oil lubrication in the continuous casting mold.

To avoid oxidic inclusions in the steel strip, it is advantageous for the steel melt to enter the continuous casting mold in the form of a pouring jet under a protective gas atmosphere. The protective gas atmosphere is formed by at least one inert gas or forming gas.

According to a preferred embodiment, the strand shell forming on the inner walls of the continuous casting mold is not exposed to any or no harmful deformations within the continuous casting mold. The choice of the cross-sectional shape itself is unaffected by this and can be chosen as desired, so that it is entirely possible to produce cast strands, for example, in which the strand thickness decreases towards the edges. It is only essential that either the selected cross-sectional format or the selected total circumference of the cast strand within the continuous casting mold is maintained unchanged from the location of the continuous shell formation until it emerges from the continuous casting mold, so that no harmful deformations and deformation forces causing this are exerted by the mold walls on the continuous shell. This does not affect the usual provision of a casting cone in the continuous casting mold in order to follow the reduction in cross-section with the mold walls that results from the shrinkage and thus to ensure that the mold walls fit tightly against the casting strand.

Constant casting and cooling conditions are necessary for uniform strand shell growth in the continuous casting mold. An important influencing variable here is a constant casting level in the continuous casting mold. This can be achieved in an expedient and simple manner if the steel melt flows through an inflow-controlled melt container before being introduced into the continuous casting mold and the setting of the casting level in the continuous casting mold is carried out by means of a trigger control. An advantageous embodiment consists in the fact that the steel melt 'before being introduced into the continuous casting mold

Inflow chamber and an outflow chamber connected to it by channels

Flows through the melt container and the melt level formed by the steel melt in the two chambers at least in one of the two chambers by adjusting the

Chamber pressure is regulated in height. A preferred embodiment results if the

The melt level in the outflow chamber is height-regulated via the melt flow rate in the channels and the level of the melt level in the inflow chamber is kept constant.

Furthermore, the object on which the invention is based is achieved by a system for producing hot-rolled steel strip from a steel melt consisting of a continuous casting system and downstream rolling devices in a system network, which is characterized in that

• That the continuous casting system has a cooled, oscillating continuous casting mold with a substantially constant mold cross section transverse to the strand pulling direction along its longitudinal extent and a melt container is arranged above this continuous casting mold, the at least one melt outlet opening of which is positioned centrally above the bath level, preferably above the mold inlet cross section, and one Shielding that seals the atmosphere seals the melt container to the continuous casting mold,

That at least one rolling device, consisting of at least one roll stand, is arranged downstream of the continuous casting plant for forming the cast strand into a steel strip,

• that the at least one rolling device is optionally preceded by a heating stage for the cast strand, and

• that the rolling device is followed by a cooling section and a coiler.

By combining these features, it is possible, on the one hand, to produce the thinnest possible cast strand in a quality that was previously only possible in slab casting plants with equidistant mold side walls and at the same time to significantly reduce the number of necessary rolling devices and to arrange them such that the heat loss of the pre-strip is minimized. A possible advantageous embodiment is that the rolling device is formed by a multi-stand finished board.

According to a further embodiment, at least two rolling devices are arranged downstream of the continuous casting installation, a first rolling device being formed by at least one rolling stand for forming a cast strand into a pre-strip, and a second rolling device for forming the pre-strip into a hot-rolled steel strip, which is followed by a second one any heating stage provided for the pre-strip is arranged immediately upstream. The rolling stands of the first rolling device are preferably formed by duo stands. According to another variant, the rolling stands of the first rolling device are formed by four-high stands.

The first rolling device is still to be assigned to the continuous casting installation, since it is operated at a rolling speed which corresponds to the casting speed of the cast strand and accordingly has measuring and control devices which enable the casting and rolling speeds to be synchronized. The roll stands of the first rolling device are advantageously formed by duo stands. When using a roll stand, which is preferably designed as a duo stand, degrees of deformation of up to 50% are achieved. In the case of two roll stands, which are preferably formed by two duo stands, degrees of deformation of up to 75% are to be applied to the cast strand.

To cut the pre-strip according to the specified coil weights, a separating device for the pre-strip, preferably scissors, is arranged after the first rolling device. The blades of these scissors are connected to mechanical or hydraulic drives. The upper knife is roof-shaped to reduce the cutting forces, so that the cutting forces occurring at cutting temperatures of approx. 1200 ° C are kept correspondingly low.

In order to minimize the length of the composite system and the heat losses of the pre-strip during its transport between the two rolling devices, an intermediate storage station for the pre-strip is arranged between the first rolling device and the heating stage, which is provided with a winding and an unwinding station. A possible embodiment of such a reel furnace is described in detail in AT-B 403 169. In this case, the two are essentially arranged one above the other Reel mandrels are used alternately as winding and unwinding stations. In addition, there is the possibility, if required, of the winding and unwinding station, and if necessary also of making the reel mandrels heatable. In a two-strand casting system, a transverse transport system, for example a coil transport carriage, is provided for introducing coils from the second casting line into the rolling line.

According to a variant of the installation according to the invention, the second rolling device is formed by a multi-stand finishing train with a descaling device upstream. With this multi-stand finishing train, depending on the casting thickness, the strip target thickness can be achieved with the use of three or four roll stands, if the first rolling device is formed by one roll stand, preferably a duo stand, and the strip target thickness can be achieved with the use of two or three roll stands , if two roll stands, preferably duo stands, are used as the first rolling device.

According to a further variant of the plant according to the invention, the second rolling device is formed by a reversing roll stand with at least one reel furnace upstream and downstream of this reversing roll stand. The number of reversing passes depends on the number of reversing stands and the strip target thickness. The production capacities between the casting plant and the rolling plant are very well coordinated if the second rolling device is formed by at least two reversing roll stands working as a tandem mill, with at least one coiler furnace upstream and downstream of these reversing roll stands. With two reversing stands working as a tandem mill, the strip target thickness is already achieved with three reversing stitches.

An advantageous embodiment is given in that scissors are arranged between the reversing roll stands and the coiler furnaces assigned to them.

An improvement of the rolled product is further achieved in that a descaling device is arranged upstream of the first rolling device. An improvement of the rolled product also occurs if the first rolling device is preceded by a heating stage. In an advantageous embodiment of the invention, the heating stage for the pre-strip is integrated in the reel furnace upstream of the second rolling device. This can be done by a heating device arranged in the reel space and, if necessary, additionally by a heatable reel mandrel. But it is also possible that the

Strip exit opening of the reel furnace forming hot strip guide with a

To equip the heating device as already described in AT-B 403 169.

An improvement in the quality of the hot-rolled steel strip arises if the rolling device (s) provided for producing a steel strip is followed by a further rolling device which is formed by at least one finishing stand and works as a skin pass mill.

In the case of continuous rolling of the steel strip, when the strip comes from the continuous casting plant without a cut through the rolling devices, it is expedient if the shears are arranged behind the cooling section.

In order to avoid reoxidation of the pouring jet when it enters the continuous casting mold, the space formed by the shield, the melt container and the continuous casting mold for the passage of the pouring jet is connected to a protective gas line according to an expedient development of the invention.

A particularly simple embodiment of the continuous casting mold in terms of production technology results if the mold cavity of the continuous casting mold is formed by two broad side walls and two narrow side walls, the mold cross section has a rectangular shape and the two broad side walls are arranged 15 to 50 mm apart, preferably 20 to 40 mm apart. According to a variant of this embodiment, the mold cavity of the continuous casting mold is formed by two broad side walls and two narrow side walls, the mold cavity cross section has a concave widening, at least in its central region, and the two broad side walls are 15 to 50 mm apart, preferably 20 to 40 mm apart, in the region of the mold outlet arranged.

In order to be able to keep the casting level in the continuous casting mold constant and at the same time to be able to clean the molten steel to be supplied from accompanying slags, the melt container contains a sealed inflow chamber and one sealed outflow chamber, the inflow chamber and the outflow chamber are positioned in the two chambers by at least one below the melt level

Channel connected and the inflow chamber and the outflow chamber are equipped with devices for regulating the casting level in the continuous casting mold. According to a preferred

Embodiment include the inflow chamber and the outflow chamber

Pressure control devices connected.

Heating devices are assigned to the melt container in order to keep the temperature of the steel melt in the melt container constant and to enable the casting operation in the area near the liquidus.

The invention is explained in more detail below with reference to the drawings of several exemplary embodiments of system configurations in a schematic representation which does not restrict the invention, FIG. 1 showing a first embodiment of a composite system according to the invention with a continuous belt pass using a multi-stand finishing train in direct assembly, FIG. 2 a second embodiment of a Composite system according to the invention using an intermediate storage station in front of a multi-stand finishing train and FIG. 3 shows a third embodiment of a composite system according to the invention using a one or two-stand reversing rolling mill. 4 illustrates the devices according to the invention for introducing the melt into the continuous casting mold according to the free jet casting process.

In the following description of three embodiments of possible composite systems, the same system components are provided with the same reference symbols.

The embodiment shown in FIG. 1 of a composite system with a continuous strip run is for the production of a steel strip with a final strip thickness of 0.6 to 12.0 mm in usual strip widths, for example 600 to 2000 mm, with a casting thickness of 15 to 50 mm, preferably 20 to 40 mm, designed and suitable in this system design for continuous rolling starting from a single-strand casting system.

The molten steel is fed into the actual continuous casting installation 1 via a trough-like distributor 2 with a holding capacity of approx. 18 t, which contains weir and dam internals, in order to ensure the corresponding residence times of the molten steel, and that Separation of non-metallic inclusions in the floating on the molten steel

Ensure distribution slag. Via a controllable by a plug control 3

The steel melt exits through a pouring tube 5 into a melt container 4 designed as a closed pure steel vessel, which is shown in detail in FIG. 4. This

Pure steel vessel is through an intermediate wall 6 in an inflow chamber 7 and in a

Outflow chamber 8 divided, the introduced into the inflow chamber 7

Steel melt through the intermediate wall 6 in the near-penetrating channels 9 in the

Outflow chamber 8 is transferred. The molten steel passes through a plurality of melt outlet openings 10 which are formed by floor nozzles and which are both round, oval and rectangular

Can have cross-section from the pure steel vessel. Heaters 41 am

Pure steel vessels ensure casting in the liquidus-near temperature range for the positive

Influencing the strand center. Inert gas or forming gas overpressure in the clean steel vessel prevents the suction of atmospheric oxygen. These measures have a positive influence on the purity of the steel to be cast and the internal quality of the cast strand.

The molten steel enters in the form of a pouring jet 11 into the mold cavity 12 of the continuous casting mold 13 and is immersed in the casting level of the molten steel that has already accumulated there. During the entry of the pouring jet into the continuous casting mold 13, the pouring jet does not come into contact with the side walls of the continuous casting mold. The pouring jet is protected against reoxidation by a bellows forming a sealing shield 14, which sealingly connects the pure steel vessel to the continuous casting mold, this sealed space 15 being held under an inert gas or forming gas pressure and being connected to an inert gas line (not shown) which flows into it . The bellows is opened for the period of the start-up process, is then automatically closed and remains closed during normal operation.

The mold cavity of the continuous casting mold is formed by straight, plane-parallel or curved broad side walls and conical or multi-conical, employed narrow side walls, the narrow side conicity being adjustable during the casting operation according to different strand shrinkages. Usually, but not illustrated, the continuous casting mold is designed as a quick-change cassette. Temperature monitoring, for example for early detection of breakthroughs, is ensured by temperature sensors in the copper plates. A hydraulic mold oscillation device enables the stroke to be adjusted during operation, Frequency and shape to achieve different oscillation modalities and good strand surfaces.

After exiting the continuous casting mold 13, the cast strand G passes through a strand guide 16 in which it is deflected from the vertical conveying direction out of the continuous casting mold into the horizontal and is fed to the rolling treatment. The strand guide can be designed both as a bending-arch straightening unit or, as shown, as a vertical bending-arch straightening unit. It usually consists of two segments. The system radius R is usually in the range of 1000 to 3000 mm.

Following the strand guide, the cast strand G, as shown in FIG. 1, enters the first roller device 17, shown in broken lines, which is formed by two duo stands 18 and undergoes a first roll deformation to a pre-strip V with a total degree of deformation of 10 to 75% subjected, whereby a tape thickness of about 6 to 30 mm is achieved. The first rolling device 17 works simultaneously as a pull-out device for the cast strand and as a roughing device, a structural separation into two individual units also being within the scope of the present invention. In exceptional cases, edge preheating before the first rolling device is necessary in order to ensure the uniform rolling temperature of about 1200 ° C. also at the strip edges. For this purpose, strip edge heating, not shown, is arranged upstream of the first rolling device. After the cooling section 23, the downstream second rolling device is followed by a separating device 19 designed as scissors.

The pre-strip is passed through a heating stage 20, in which it is heated to a rolling temperature of approximately 1000 to 1250 ° C. Immediately afterwards, the pre-strip is introduced into a second rolling device 21, formed by a multi-stand finishing train F1, F2,... With a preceding, highly efficient descaling device 22. The descaling device 22 is preferably a rotor descaling which enables a high impact pressure with small amounts of water. Following the multi-stand series, the steel strip S hot-rolled to the final target thickness of 0.6 to 12.0 mm passes through the cooling section 23 and is cut to length in a coiler 24. The cooling section 23 is divided into a main cooling section and a precision cooling section (not shown) and offers the possibility of responding to different mechanical and technological target values for different types of steel. The Recording the current temperatures with appropriate measuring systems and the integration of thermo-mathematical cooling models enable optimal temperature control.

1 shows two possible embodiments of the composite system according to the invention: in the first embodiment, the first rolling device 17 is omitted; the remaining second rolling device 21, now the only rolling device, consists of one to five-stand finishing train F1, F2, F3, ... The second embodiment consists of a one- to two-stand first rolling device 17 and a multi-stand second rolling device 21.

FIG. 2 shows an embodiment of a composite system according to the invention, which has the following differences in the system configuration compared to the embodiment known from FIG. 1, the same system components being provided with the same reference numerals: With the first rolling device 17, which is provided by one or two duo stands 18 is formed, a pre-strip of 6 to 35 mm thick is produced (degree of deformation 10 to 75%), cut to length according to the desired coil weight with the scissors 19, wound up in an intermediate storage station 26, optionally stored, unwound, in a heating stage 20 to the rolling temperature brought and a two- to four-stand finishing train Fl, F2, F3, F4 is fed. With a corresponding design of the intermediate storage station 26, pre-strip bundles can be fed from a multi-strand continuous casting installation to a single multi-frame prefabricated group F1, F2, F3. For this purpose, each casting strand is assigned a winding station 27 and a removal station 28, as well as a coil carriage (not shown) for introducing the bundles into the rolling line 29. A temperature homogenization takes place in the intermediate storage station 26, which may be amplified by a heating device. The casting and the rolling process are decoupled, as a result of which the feed rate of the pre-strip to the second rolling device 21 can be selected independently of the casting speed and thus faster.

A further embodiment of the composite system according to the invention, in which the second rolling system 21 is formed by a reversing roll stand 30 or optionally by two reversing roll stands 30, 31 interacting in the manner of a tandem mill, can be seen in a schematic illustration in FIG. 3. Fig. 3 also shows several variants of a composite system, the core devices of which are formed by a casting system and a reversing roll stand. The reversing roll stands 30, 31 each have a coiler 32, 33 upstream and downstream. A casting installation, as has already been described in detail in the description of FIG. 1, is connected to duo-roll stands 18, which may be arranged downstream, as first rolling device 17. A highly efficient descaling 34 is positioned in front of the first rolling device 17. A heating stage 35, for example a short heating section or an edge heating device using gas burners, is only necessary in exceptional cases, in the event of faults or special steel qualities or small hot strip end thicknesses. After being cut to length, the pre-strip is wound into a bundle with scissors 19 in an intermediate storage station 26. The intermediate storage station consists of a reel furnace with two separate winding and unwinding stations 38 which are arranged one above the other. The end of the strand is cut off with the scissors 39 in order to produce an ideal tapping cross section for the next rolling pass. This is followed by the second roll pass and end cut with the scissors 39a in the return. Three roll passes are usually sufficient to achieve the final roll thickness. During the reversing rolling process, with the incorporation of the reel furnace 38, the next pre-strip is simultaneously wound up in the second reel furnace 37. With special design of the reel furnaces 32, 33, 37, 38, as described, for example, in AT-B 403 169, in which A complete strip feed into the reel furnace is possible, a temperature homogenization is carried out over certain dwell times of the preliminary strip in the reel furnace of about 2 minutes. Due to the high enthalpy temperature of this process at around 1200 ° C, hot strip with a thickness of less than 1.0 mm can be produced with a high output, which is considerably below the production range of conventional Steckel rolling mills.

Following the reversing roll stand, the hot-rolled steel strip passes through up to two finishing stands 40 which act as skin pass stands before it enters the downstream cooling section 23 and is then wound up in the coiler 24.

Claims

Expectations:

1. Process for the production of hot-rolled steel strip from a molten steel, consisting of the following successive steps:

Continuous introduction of a molten steel into a cooled, oscillating continuous casting mold (13) according to the free jet casting process, the pouring jet being shielded from atmospheric influences,

Conveying an at least partially solidified cast strand (G) out of the continuous casting mold (13) with a strand thickness of 15 to 50 mm,

If necessary, heating the cast strand to the rolling temperature in a heating stage (20) immediately before the cast strand is deformed,

• Cooling the steel strip (S) in a downstream cooling section (23) and reeling the strip in a coiler (24).

2. The method according to claim 1, characterized in that the at least partially solidified cast strand is conveyed out of the continuous casting mold with a strand thickness of 20 to 40 mm.

3. The method according to any one of claims 1 or 2, characterized in that the roll forming of the cast strand into a steel strip is carried out in at least one rolling stage.

4. The method according to claim 3, characterized in that a first roll forming of the cast strand into a pre-strip (V) in a first rolling stage with a degree of deformation of 10 to 75% and that a further, second roll forming of the pre-strip into a steel strip (S) takes place in a second rolling stage immediately following a case-by-case heating of the pre-strip to the rolling temperature.

5. The method according to claim 4, characterized in that the pre-strip formed by the first roll forming of the cast strand before the second roll forming, if necessary before heating to the rolling temperature, is cut to length according to predetermined coil weights.

6. The method according to any one of claims 4 or 5, characterized in that the pre-cut strip is wound into a bundle in an intermediate storage station (26), optionally stored and then unwound again, heated to the rolling temperature and fed to the second roll deformation.

7. The method according to any one of claims 4 or 5, characterized in that the pre-cut strip is wound into a bundle in an intermediate storage station (26), optionally stored, heated to the rolling temperature, unwound and fed to the second roll forming.

8. The method according to any one of claims 4 to 7, characterized in that the second roll forming is carried out by reversing rolls.

9. The method according to any one of claims 1 to 4, characterized in that the steel strip produced by roll forming is cut to length in accordance with predetermined coil weights after cooling in the cooling section (23).

10. The method according to any one of claims 1 to 9, characterized in that the casting speed is adjusted from 3 to 12 m / min.

11. The method according to any one of claims 1 to 10, characterized in that the steel melt in the form of a free pouring jet (11) enters the continuous casting mold (13) under a protective gas atmosphere.

12. The method according to any one of claims 1 to 11, characterized in that the protective gas atmosphere is formed by at least one inert gas or a forming gas.

13. The method according to any one of claims 1 to 12, characterized in that the strand shell forming on the inner walls of the continuous casting mold (13) is not exposed to any harmful deformations within the continuous casting mold.

14. The method according to any one of claims 1 to 13, characterized in that the molten steel flows through an inflow-controlled melt container (4) before being introduced into the continuous casting mold (13) and the setting of the casting level in the continuous casting mold (13) takes place via a deduction control.

15. The method according to claim 14, characterized in that the molten steel before introduction into the continuous casting mold (13) an inflow chamber (7) and with it through channels (9) connected outflow chamber (8) of a melt container (4) and flows through the melt level formed in the two chambers is controlled at least in one of the two chambers by adjusting the chamber pressure.

16. The method according to claim 15, characterized in that the melt level in the outflow chamber (8) is height-regulated via the melt flow in the channels (9) and the level of the melt level in the inflow chamber (7) is kept constant.

17. Plant for the production of hot-rolled steel strip from a steel melt consisting of a continuous casting plant (1) and at least one downstream rolling device (21) in a plant network, characterized in that

• That the continuous casting plant (1) has a cooled, oscillating continuous casting mold (13) with a substantially constant mold cavity cross section transverse to the strand extraction direction along its longitudinal extent and a melt container (4) is arranged above this continuous casting mold, the at least one melt outlet opening (10) being located centrally above the bath level , is preferably positioned above the mold inlet cross section and a shield sealing the pouring jet to the atmosphere connects the melt container (4) to the continuous casting mold (13) in a sealing manner,

That at least one rolling device (21), consisting of at least one rolling stand, for forming the cast strand (G) into a steel strip (S) is arranged downstream of the continuous casting installation, • that the at least one roller device (21) is optionally preceded by a heating stage (20) for the cast strand, and

• That the rolling device (21) is followed by a cooling section (23) and a reel system (24).

18. Plant according to claim 17, characterized in that the rolling device (21) is formed by a multi-stand finishing series (Fl, F2, F3, ...).

19. Plant according to claim 17, characterized in that at least two rolling devices (17, 21) are arranged downstream of the continuous casting plant, a first rolling device (17) being formed by at least one roll stand for forming a cast strand (G) into a pre-stiffener (V) and this is followed by a second rolling device (21) for shaping the pre-strip (V) into a hot-rolled steel strip (G), with a second heating device (21) optionally provided upstream of a heating stage (20) for the pre-strip.

20. Plant according to claim 19, characterized in that the rolling stands of the first rolling device (17) are formed by dual stands (18).

21. Plant according to claim 19, characterized in that the rolling stands of the first rolling device (17) are formed by four-high stands.

22. Plant according to one of claims 19 to 21, characterized in that the first rolling device (17) is followed by a separating device (19) for the pre-strip, preferably scissors.

23. Installation according to one of claims 19 to 22, characterized in that an intermediate storage station (26) for the pre-strip is arranged between the first rolling device (17) and the heating stage (20), which has a winding and an unwinding station (27, 28; 37, 38) is provided.

24. Plant according to one of claims 19 to 23, characterized in that the second

Rolling device (21) is formed by a multi-stand finishing train (Fl, F2, F3) with a descaling device (22) upstream.

25. Plant according to one of claims 19 to 23, characterized in that the second rolling device (21) of a reversing roll stand (30) with at least one upstream and downstream of this reversing roll stand (32, 33, 37, 38) is formed.

26. Plant according to one of claims 19 to 23, characterized in that the second rolling device (21) of at least two reversing roll stands (30, 31) working in tandem operation with at least one upstream and downstream of this reversing roll stand (32, 33) is.

27. Plant according to one of claims 25 or 26, characterized in that between the reversing roll stands (30, 31) and the associated reel furnace (32, 33) scissors (39, 39a) are arranged.

28. Plant according to one of claims 25 or 26, characterized in that a

Descaling device (34) upstream of the first rolling device (17).

29. Plant according to one of claims 25 or 26, characterized in that the first rolling device (17) is preceded by a heating stage (35).

30. Plant according to one of claims 23 to 29, characterized in that in the intermediate storage station (26) on the egg stage (20) for the pre-strip is integrated.

31. Plant according to one of claims 17 to 30, characterized in that the rolling device (s) (17, 21) provided for producing a steel strip is followed by a further rolling device formed at least by a finishing stand and acting as a skin pass mill (40).

32. Installation according to one of claims 17 to 21 and 24, characterized in that the cooling section (23) is followed by a pair of scissors (19).

33. System according to one of claims 17 to 32, characterized in that the space (15) formed by the shield (14), the melt container (4) and the continuous casting mold (13) for the passage of the pouring jet is connected to a protective gas supply line.

34. System according to one of claims 17 to 33, characterized in that the mold cavity of the continuous casting mold (13) is formed by two broad side walls and two narrow side walls, the mold cavity cross section has a rectangular shape and the two broad side walls 15 to 50 mm apart, preferably 20 to 40 mm mm are arranged away.

35. Installation according to one of claims 17 to 34, characterized in that the mold cavity of the continuous casting mold (13) is formed by two broad side walls and two narrow side walls, that the mold cavity cross section has a concave extension at least in its central region, and the two broad side walls in the region of Mold exit are 15 to 50 mm, preferably 20 to 40 mm apart.

36. Installation according to one of claims 17 to 35, characterized in that the melt container (4) contains a sealed inflow chamber (7) and a sealed outflow chamber (8), the inflow chamber (7) and the outflow chamber (8) by at least one below the melt level in the two chambers positioned channel (9) are connected and the inflow chamber (7) and the outflow chamber (8) are equipped with devices for regulating the casting level in the continuous casting mold.

37. Plant according to claim 36, characterized in that the inflow chamber (7) and the

Outflow chamber (8) are connected to pressure regulating devices.

38. Installation according to one of claims 1 to 37, characterized in that the melt container (4) heating devices are assigned.