EP2627465B1 - Energy- and yield-optimized method and plant for producing hot steel strip - Google Patents

Description

Technical area

The invention relates to a method for the continuous or semicontinuous production of steel hot strip, which is rolled starting from a guided through a strand guide strand in a roughing train to an intermediate belt and subsequently in a finishing train to an end belt, according to claim 1 and a corresponding plant for Implementation of this method according to claim 17.

One speaks of continuous production or "endless rolling" when a casting plant is connected to a rolling mill, that cast in a mold casting the strand directly - without separation from the straight cast strand part and without intermediate storage - in a rolling plant and there on a respective desired final thickness is rolled. The beginning of the strand can therefore already be finished rolled to a steel strip to the final thickness, while the casting plant continues to pour on the same strand, so there is no end of the strand exists. One speaks also of directly coupled operation or endless operation of the casting and rolling plant.

In the semicontinuous production or "semi-continuous rolling" the cast strands are divided after casting and fed the separated strands or slabs without intermediate storage and cooling to ambient temperature of the rolling mill.

The strand emerging from the mold of the casting plant first passes through a strand guiding device directly following the mold. The strand guiding device, also referred to as "strand guiding corset", comprises a plurality (usually three to six) guiding segments, each guiding segment comprising one or more (usually three to ten) pairs of guiding elements, preferably designed as strand supporting rollers. The support rollers are rotatable about an axis orthogonal to the transport direction of the strand.

Instead of strand support rolls, individual guide elements may also be used as static, e.g. run skid-shaped components.

Regardless of the specific design of the guide elements, these are arranged on both sides of the strand broad sides, so that the strand is guided by upper and lower guide element series and conveyed to a roughing mill.

More precisely, the strand is supported not only by the strand guiding device, but also by a lower end portion of the mold, which is why the mold could also be regarded as part of the strand guiding device.

The Strangerstarrung begins at the upper end of the (run) kokille at the bath level, the so-called "meniscus", the mold is typically about 1m long (0.3-1.5m).

The strand exits vertically downward from the mold and is deflected into the horizontal. The strand guiding device therefore has a course substantially curved over an angular range of 90 °.

The emerging from the strand guide device strand is reduced in thickness in the roughing mill (HRM, High-Reduction Mill), the resulting intermediate band is heated by means of a heater and rolled finished in a finishing train. In the finishing train is hot rolled, that is, the rolling stock has a temperature above its recrystallization temperature during rolling. For steel this is the range above about 750 ° C, usually is rolled at temperatures up to 1200 ° C warm.

During hot rolling of steel, the metal is usually in the austenitic state, where the iron atoms are arranged cubic face centered. One then speaks of rolls in the austenitic state, when both the initial and the final rolling temperature are in the austenitic region of the respective steel. The austenite area of a steel depends on the steel composition, but is usually above 800 ° C.

Decisive parameters in the production process of steel hot-rolled strip-casting systems are the casting speed with which the strand leaves the mold (and passes through the strand guide device) and the mass flow rate, which is the product of the casting speed with the thickness of the strand and usually the unit carries [mm * m / min].

The steel strips produced are processed, inter alia, for motor vehicles, household appliances and the construction industry.

State of the art

From the prior art, the continuous and semi-continuous production of steel hot tapes is already known. Due to the coupling of caster and rolling mill Mastering all plant parameters is a high technical process requirement. Modifications in the casting and rolling process, in particular by changing the casting speed in combination with the strand thickness as well as a material-specific solidification coefficient that can be controlled by cooling have a considerable effect on the production quality and energy efficiency of the plant.

Generic methods or systems are eg off EP 0 415 987 B1 . EP 1 469 954 B1 and DE 10 2007 058 709 A1 and WO 2007/086088 A1 known.

Significant advances in hot rolling technology have been made especially by Acciaieria Arvedi S.p.A. which has developed an ISP technology (in-line strip production) based thin slab continuous process under the name Arvedi ESP (Endless Strip Production).

In this ESP method, the casting and rolling processes are combined in a particularly advantageous manner, so that subsequent cold rolling is no longer required for many steel heat-sealing qualities. With such steel heat-tape grades, in which subsequent cold-rolling is still required, the number of rolling stands can be reduced compared to conventional rolling mills.

For example, in the Rolling & Processing Conference '08 (September) and installed in Cremona, Italy ESP plant for steel hot strip production of the company Arvedi comprises a subsequent to a continuous caster Vorwalzstraße with three roughing stands, two band-separating devices, an induction furnace for intermediate heating of the pre-rolled intermediate strip, followed by a finishing train with five finishing stands. The from the pre-rolling emerging end band is cooled in a cooling section and wound by means of three underfloor reels to tape rolls with a weight of up to 32 tons. The underfloor coiler is preceded by a separation device in the form of a high-speed shear. Depending on the steel grades and the strength of the rolled steel strip, the production capacity of this single-stranded production line is about 2 million tonnes per year (mtpy). This appendix is also described in the following publications: Hohenbichler et al: "Arvedi ESP - technology and plant design", Millenium Steel 2010, March 1, 2010, pages 82-88 . London, and Siegl et al: "Arvedi ESP - First Tin Slab Endless Casting and Rolling Results", 5th European Rolling Conference, London, June 23, 2009 ,

In particular, too short a strand support length of 17 m, which is that more accurately called "metallurgical length" distance between the spout area of the mold proves to be disadvantageous, specifically between the designated as "meniscus" mirror of the liquid steel and the pre-rolling facing end of the A strand guide device.

As already described above, the strand guiding device forms between the guide elements or the strand support rollers a partially curved receiving shaft for receiving the freshly cast (still having a liquid core) strand.

As the end of the strand guiding device is thus understood in the present context intended for strand contacting guide surface or surface line of the last of the roughing facing guide element or the last support roller of the upper guide elements series.

With increasing distance from the meniscus guided in the strand guiding device strand or located in its original form steel strip cools more and more. The inner region of the strand, which is still liquid or pasty-marshy consistency, is referred to below as the liquid sump. A kokillenfernere "Sumpfspitze" of the liquid sump is defined as that central cross-sectional area of the strand, in which the temperature just corresponds to the steel solidus temperature and then drops below this. The temperature of the sump tip therefore corresponds to the solidus temperature of the respective steel grade (typically between 1300 ° C and 1535 ° C.

The rolling of a completely solidified or cooler cast strand requires a much higher energy expenditure than the rolling of a cast strand with a hot cross-sectional core.

For volume flows below 380-400 mm * m / min, so far only a discontinuous production ("batch operation") has taken place in the ISP or ESP process.

Known from the prior art CSP (Compact Strip Production) method work at strand thicknesses of 45-65 mm also with flow rates below about 400 mm * m / min using a roller hearth furnace with a length of 250 m and more, with only one discontinuous production ("batch operation") or a semicontinuous production takes place. In the latter, 3-6 separated strands or slabs (no longer connected to the casting machine or die) are continuously rolled.

In the EP 0 889 762 B1 For continuous casting and rolling of hot strip, a volumetric flow> 0.487 mm ² / min (converted to the usual unit mentioned at the beginning:> 487 mm * m / min). However, casting with such a high volume flow at a relatively low strand thickness proves to be too fast for many steel grades in order to be able to ensure sufficient production quality.

Presentation of the invention

In the course of increasing cost and production pressure, the aim is to increase the capacity of the plant while further optimizing the production of steel hot-rolled strip for a variety of steel grades, cooling parameters and strand thicknesses.

The energy efficiency of generic systems for the production of steel hot strip is to be increased, thereby enabling a more economical production.

In order to optimally utilize the casting heat during the production process of hot strip steel, it should be ensured that the sump tip, d.i. the just still doughy cross-sectional core of the strand conveyed in the strand guide device is always as far as possible from the mold and as close as possible to the end of the strand guide device and thus as close as possible to the entrance to the roughing mill.

In this task, it should be taken into account that, depending on a material-specific solidification factor and a respectively set strand thickness, the casting speed or the volume flow passing through the strand guiding device may not be too large, since in such a case the swamp tip is moved beyond the strand guiding device and thus Inflation and bulging of the strand or the steel heat tape could take place.

The above objects are achieved by a method having the features of claim 1 and an annex having the features of claim 17.

• bei Gießgeschwindigkeiten zwischen 3,8 und 5,0 m/min mit 100 - 120 mm Strangdicke, vorzugsweise mit 110 bis 120 mm Strangdicke,
• bei Gießgeschwindigkeiten zwischen 5,0 und 5,9 m/min mit 85
• 110 mm Strangdicke, vorzugsweise mit 95 bis 110 mm Strangdicke,
• bei Gießgeschwindigkeiten größer oder gleich 5,9 m/min mit maximal 102 mm Strangdicke.

A process for the continuous or semicontinuous production of steel hot strip, which is rolled starting from a guided through a strand guide strand in a roughing to an intermediate strip and subsequently in a finishing train to a final strip according to the invention is characterized in that cast in a casting line strand a Strand thickness between 105 and 130 mm, preferably a strand thickness between 115 and 125 mm, and in the Liquid Core Reduction (LCR) method by means of the subsequent strand guiding device at liquid cross-sectional core of the strand to a thickness between 95 and 120 mm, preferably to a Thickness between 95 and 115 mm is reduced, with a measured between the meniscus, ie the casting level of the caster and one of the roughing line facing the end of the strand guide device strand support length is greater than or equal to 18.5 m, preferably in a range between 18.7 and 23 m, more preferably between 20.1 and 23 m, and wherein a casting speed v _{c is} in a range of 3.8 to 7 m / min. The strands are cast with different strand thicknesses depending on the following casting speeds:

• at casting speeds between 3.8 and 5.0 m / min with 100-120 mm strand thickness, preferably with 110-120 mm strand thickness,
• at casting speeds between 5.0 and 5.9 m / min with 85
• 110 mm strand thickness, preferably with 95 to 110 mm strand thickness,
• at casting speeds of greater than or equal to 5.9 m / min with a maximum of 102 mm strand thickness.

By using these casting parameters according to the invention, on the one hand, a high production quality is ensured by the bottom tip of the strand always reaching close to the end of the strand guiding device regardless of the respective material quality-dependent maximum casting speeds, on the other hand an extraordinarily high production capacity is achieved.

The steel strip has a sufficiently hot cross-sectional core during its reduction in thickness in the downstream of the strand guide device Vorwalzstraße to be rolled with relatively little energy.

The energy consumption when rolling steel heat band is thus significantly reduced and increased the efficiency of generic systems.

Calculations have shown that when using casting parameters according to the invention in strands between 1400 and 1850 mm width a production capacity of more than 3 million tons per year (MTpy) are possible, which compared to systems or methods according to the prior art means a big increase and a much more economical production of steel hot-rolled allows, but without risking quality loss. By means of a method according to the invention, it is also possible to process steel grades which are not at all suitable for a continuous or endless production process according to the prevailing opinion to date.

• bei Gießgeschwindigkeiten zwischen 3,8 und 5,0 m/min mit 100 - 120 mm Strangdicke, vorzugsweise mit 110 bis 120 mm Strangdicke,
• bei Gießgeschwindigkeiten zwischen 5,0 und 5,9 m/min mit 85
• 110 mm Strangdicke, vorzugsweise mit 95 bis 110 mm Strangdicke,
• bei Gießgeschwindigkeiten größer oder gleich 5,9 m/min mit maximal 102 mm Strangdicke.

In order to further optimize the method according to the invention, special process parameters were determined by calculations and experimental arrangements, which allow a manufacturing advance in terms of manufacturing quality and energy efficiency in the production of steel hot strip. According to the invention, it is provided that strands having different strand thicknesses are cast in dependence on the following casting speeds:

• at casting speeds between 3.8 and 5.0 m / min with 100-120 mm strand thickness, preferably with 110-120 mm strand thickness,
• at casting speeds between 5.0 and 5.9 m / min with 85
• 110 mm strand thickness, preferably with 95 to 110 mm strand thickness,
• at casting speeds of greater than or equal to 5.9 m / min with a maximum of 102 mm strand thickness.

Such an adjustment of respective strand thicknesses as a function of respective (steel-specific) maximum casting speeds ensures that the bottom tip of the strand - with the exception of the Angießphase - always held reasonably close to the end of the strand guide device and thus the casting heat can be optimally utilized to increase the efficiency of subsequent rolling processes.

In accordance with the invention, it is further contemplated that in the rough rolling mill, roughing of the billet into an intermediate belt is accomplished in at least four passes, i. using four roughing stands, preferably in five rolling passes, i. carried out using five roughing stands.

While in processes according to the prior art usually a rough rolling of the strand is carried out in three rolling passes, the energy efficiency of the rolling process can be further increased by an inventive four or five rolling passes. By four or five rolling passes are performed in rapid succession, the casting heat still in the strand is optimally utilized. Furthermore, when four or five rolling passes are made, a very narrow thickness range of the intermediate strip (between 3 and 15 mm, preferably between 4 and 10 mm) is achieved, so that a downstream of the roughing mill heater, such as a cross-field inductive heating furnace, designed exactly to a specific thickness range of the intermediate band can be. Energy losses due to a too large dimensioning of the recording of the heater can thus be avoided.

In addition, it is provided that the four or five rolling passes taking place in the rough rolling mill take place within a maximum of 80 seconds, preferably within a maximum of 50 seconds.

According to a preferred embodiment of the invention, it is provided that the first rolling pass in the roughing mill takes place within a maximum of 7 minutes, preferably within a maximum of 6.2 minutes, from the start of solidification of the liquid extruded steel present in the casting plant. Ideally, the first pass in the roughing mill takes place within a maximum of 5.8 minutes, even at casting speeds in the region of 4 m / min.

According to a further preferred embodiment of the invention, it is provided that between the end of the strand guiding device and an inlet region of the roughing train only a cooling of the strand caused by the ambient conditions in the form of natural convection and radiation is allowed, i. no artificial cooling of the strand takes place by means of a cooling device.

According to a further preferred embodiment of the invention, it is provided that in the roughing mill per Rolling a reduction in the thickness of the strand by 35-60%, preferably by 40-55% occurs. With a provision of exactly four roll stands, it follows that an intermediate strip with a thickness of approximately 3 to 15 mm, preferably with a thickness of 4 to 10 mm, leaves the rough rolling line 4.

According to a further preferred embodiment variant of the invention, it is provided that a temperature loss rate of the intermediate strip emerging from the rough rolling mill is below a maximum of 3 K / m, preferably below a maximum of 2.5 K / m. It would also be conceivable to realize temperature loss rates <2 K / m. Such a temperature loss rate is achieved by heat radiation and / or convection from the intermediate belt and can be controlled by an appropriate choice of thermal boundary conditions (covers, tunnels, cold air, humidity, ...) and transport speed or mass flow.

According to a further preferred embodiment of the invention, it is provided that heating of the intermediate strip leaked from the roughing train by means of an inductive heating device, preferably in the transverse field heating method, starting at a temperature above 770 ° C, preferably above 820 ° C to a temperature of at least 1110 ° C, preferably to a temperature above 1170 ° C.

According to a further preferred embodiment of the invention, it is provided that the heating of the intermediate band takes place within a time period of 4 to 25 seconds, preferably within a period of 5 to 13 seconds.

According to a further preferred embodiment variant of the invention, it is provided that when exactly four rolling passes are made in the rough rolling mill, the time interval between the first pass and the inlet to the heating device does not exceed 105 seconds for intermediate strip thicknesses of 5-10 mm, preferably not longer than 70 seconds.

In compliance with these parameters results in a very compact system in which the distance of the heater to the casting plant or Vorwalzstraße is kept very low, which allows a thermal efficiency advantage.

According to a further preferred embodiment of the invention, it is provided that a finish rolling of the heated intermediate strip in the finishing train in four rolling passes, i. using four finishing stands or in five rolling passes, i. using five finishing stands to an end strip with a thickness of <1.5 mm, preferably <1.2 mm. By means of a method according to the invention, rolling to final thicknesses of <1 mm is also possible.

According to a further preferred embodiment variant of the invention, it is provided that the rolling passes carried out within the finishing train through the five or four finishing mills take place within a maximum period of 16 seconds, preferably within a maximum period of 8 seconds.

According to a further preferred embodiment variant of the invention, predetermined guide elements of the strand guiding device are (transversely) adjustable relative to a longitudinal axis of the strand for liquid core reduction (LCR) thickness reduction of the strand for its contacting, wherein an adjustment of the guide elements is made depending on the material of the strand and / or the casting speed in order to reduce the strand thickness by up to 30 mm.

According to one embodiment of the invention, it is provided here that the strand thickness quasi-static, i. shortly after the start of pouring or the casting of a casting sequence, as soon as the "leading strand area", referred to as the "strand head", has passed the guide elements intended for reducing the thickness, it is set once.

In a particularly preferred embodiment, however, provision may also be made for the strand thickness to be dynamically adjustable, i. is arbitrarily variable during the casting process or during the passage of the strand through the strand guiding device. The dynamic setting is then preferably set by the operating team depending on the steel grade and the actual casting speed, if this changes only on a case-by-case basis. The LCR thickness reduction is between 0 and 30 mm, preferably between 3 and 20 mm.

In a preferred embodiment of the dynamic application of LCR, this function can also be taken over by an automated device, especially if very frequent changes in thickness or speed would be usual or necessary.

The relationship between the setting of the strand thickness in connection with the casting speed is carried out by means of inventively proposed speed factors K, the selection of which is effected as a function of the strand support length and the quality of the extruded steel.

Corridor areas are specified for the speed factor K, within which a casting operation can be carried out efficiently and meaningfully.

The cooling characteristic of respective steel grades has a great influence on the position of the sump tip within the strand. Fast-setting steel grades allow the system to operate at relatively high casting speeds v _c , while lower casting speeds v _{c are} to be selected for slower-setting steel grades in order to prevent bulging and bursting of the strand in the area of the swamp tip. In connection with the speed of the cooling of the strand, one speaks of "hard cooling" (rapid solidification), "medium hard cooling" and "soft cooling" (rather slow solidification).

To cool the strand, a coolant, preferably water, is applied to this in the region of the strand guiding device (between the end of the mold and the end of the strand guiding device facing the rough rolling mill). The application of the coolant to the strand takes place by means of an injection device, which can comprise any desired number of spray nozzles.

For a hard cooling 3 to 4 liters of coolant per kg of extruded steel are used, while for a medium-hard cooling 2 to 3.5 liters of coolant per kg of extruded steel and for a soft cooling <2.2 liters of coolant per kg extruded steel are used. The quoted amounts of coolant for hard, medium hard and soft cooling overlap, since the realization of a hard, medium-hard or soft cooling in practice not only on the amount of coolant, but also on the structural design of the spray device, in particular the Düsenaufbauart (es exist pure water nozzles and air / water nozzles, so-called "2-phase nozzles"). Other influencing factors for the speed of strand cooling are the design of the guide elements or strand support rollers of the strand guide device (internal or shell-cooled strand support rollers), the arrangement of the support rollers, in particular the ratio of the support roller diameter to the distance between adjacent support rollers, the spray character of the nozzles and the coolant or water temperature.

Within the corridor areas proposed according to the invention, the choice of a specific speed factor K takes place in particular as a function of the steel grade or the cooling characteristic of the strand. For steel grades to be cooled rapidly, a speed factor K lying in the upper region of a corridor region proposed according to the invention can be used, while for slower steel grades a velocity factor K lying in the middle or lower region of a corridor region proposed according to the invention is used.

Thus, it is provided according to a process engineering optimization that for a hard to be cooled by means of a spraying device in the strand guide device rod steels, ie with the application of 3 to 4 liters of coolant per kg of extruded steel, in a stationary-continuous operation of the system, the relationship of in [mm measured strand thickness d with the casting speed v _c measured in [m / min] is maintained according to the formula v _c = K / d ² , wherein a velocity factor K contained in the formula at a strand support length L = 17.5 m in a corridor range of 42000 to 48900, preferably in a corridor range from 45500 to 48900, while the Speed factor K at a strand support length L = 23 m in a corridor range of 55200 to 64600, preferably in a corridor range from 59900 to 64600, wherein for determining (target) casting speeds v _c or (target) strand thickness d for facilities with between the Strand support lengths L = 17.5 m and L = 23 m lying strand support lengths L an interpolation between the corridor areas mentioned above is feasible.

Under a stationary-continuous operation of the system are understood in the present context operating phases with a period> 10 minutes, during which the casting speed is substantially constant. On the one hand, the definition of steady-state plant operation merely serves to delimit against a gating phase during which the liquid steel initially passes through the strand guiding device and during which the casting speed is subject to extraordinary parameters or, on the other hand, also acceleration phases which are possible in the meantime to increase the throughput and / or operationally required Deceleration phases (when the liquid steel delivery has to be maintained or because of strand quality, lack of cooling water, ...).

For medium hard-to-cool extruded steels, ie by applying 2 to 3.5 liters of coolant per kg of extruded steel, the relationship of a strand thickness d measured in [mm] with the casting speed measured in [m / min] is determined in a stationary continuous operation of the plant v _{c is satisfied} according to the formula v _c = K / d ² , wherein a speed factor K contained in the formula at a strand support length L of 17.5 m in a corridor range from 39600 to 46500, preferably in a corridor range from 43050 to 46500 while the speed factor K is at a strand support length L = 23 m in a corridor range of 52100 to 61900, preferably in a corridor range of 57000 to 61900, where for determining (target) casting speeds v _c or (target) strand thicknesses d for Installations with strand support lengths L lying between the strand support lengths L = 17.5 m and L = 23 m, an interpolation between the corridor regions mentioned above can be carried out.

For soft-to-cool extruded steels, ie with the application of less than 2.2 liters (preferably between 1.0 and 2.2 liters) of coolant per kg of extruded steel, in a steady-state operation of the plant, the relationship of one measured in [mm] Strand thickness (d) with the casting speed v _c measured in [m / min] according to the formula v _c = K / d ² , where a speed factor K contained in the formula at a strand support length L of 17.5 m in a corridor range of 37100 to 44100, preferably in a corridor range from 40600 to 44100, while the speed factor K is at a strand support length L = 23 m in a corridor range of 48900 to 59000, preferably in a corridor range of 53950 to 59000, wherein for the determination of (target) Casting speeds v _c or (target) strand thicknesses d for installations with strand support lengths L between the strand support lengths L = 17.5 m and L = 23 m, an interpolation between the vora the corridor areas listed below.

The detailed / refined choice of the speed factor is in addition to the strand support length in particular from the carbon content of the cast steels, their solidification or Transformationcharacteristics, their strength or ductility properties, etc. dependent.

An operational management according to the invention proposed speed factors K allows optimal utilization of the casting heat contained in the strand for the subsequent rolling process and an optimization of the material throughput and thus a productivity advantage (with operational decrease of the casting speed, the strand thickness can be increased and thereby the material throughput can be increased).

Claim 17 is directed to a system for carrying out the method according to the invention for the continuous or semi-continuous production of steel strip, comprising a casting plant with a mold, a subordinate strand guiding device, a downstream Vorwalzstraße, one of these downstream, inductive heating and one of these downstream finishing train, said the strand guiding device has a lower series of guide elements and a parallel or converging arranged upper series of guide elements and formed between the two guide element series for receiving the strand emerging from the casting strand receiving shaft, which by forming different distances between opposing guide elements to each other in the transport direction the strand is at least partially tapered and thus the strand is thickness reducible. According to the invention, provision is made for the clear receiving width of the receiving shaft to be between 105 and 130 mm, preferably between 115 and 125 mm, at its input to the mold, such that the receiving shaft has at its end facing the rough rolling mill a light density corresponding to the strand thickness of the strand Receiving width between 95 and 120 mm, preferably between 95 and 115 mm, wherein a between the casting level of the caster and the Vorwalzstraße facing the end of the receiving shaft of the strand guide device measured strand support length is greater than or equal to 18.5 m, preferably in a range between 18, 7 and 23 m, more preferably between 20.1 and 23 m, and wherein a control device is provided, by means of which the casting speed v _{c of} the strand 3 in a range between 3.8 - 7 m / min is durable, and that the Pre-rolling mill comprises four or five roughing stands.

According to a preferred embodiment of the system according to the invention, it is provided that no cooling device, but a thermal cover is provided between the end of the receiving shaft and the strand guide device and an inlet region of the roughing, at least partially surrounding a conveyor device provided for transporting the strand and thus a Cooling of the strand delayed.

According to a further preferred embodiment variant of the system according to the invention, it is provided that a reduction in the thickness of the strand by 35-60%, preferably by 40-55% per roughing mill feasible by Vorwalzgerüst arranged in the roughing mill, so that an intermediate strip with a thickness from 3 to 15 mm, preferably with a thickness of 4 to 10 mm can be generated.

According to a further preferred embodiment of the system according to the invention, it is provided that the heating device as an inductive transverse field heating furnace is formed, by means of which the strand, starting at a temperature above 770 ° C, preferably above 820 ° C to a temperature of at least 1110 ° C, preferably to a temperature of above 1170 ° C can be heated.

According to a further preferred embodiment variant of the system according to the invention, it is provided that the finishing train comprises four or five finishing mills, by means of which an intermediate strip emerging from the roughing train can be reduced to an end strip with a thickness <1.5 mm, preferably <1.2 mm.

According to a further preferred embodiment of the system according to the invention, it is provided that the finishing mills are arranged at intervals of <7 m, preferably at intervals of <5 m to each other, wherein the distances between the working roll axes of the finishing mills are measured.

According to a further preferred embodiment of the system according to the invention, it is provided that certain guide elements (gap) are adjustable to reduce the thickness of the strand and thereby a clear receiving width of the receiving shaft is reduced or increased, the strand thickness or the clear receiving width depending on the material of the strand and / or the casting speed is adjustable.

According to a further preferred embodiment of the system according to the invention, it is provided that the adjustable guide elements are arranged in a front half facing the mold, preferably in a front quarter of the longitudinal extension of the strand guide device facing the mold.

In order to ensure at least during the first two rolling passes the presence of a strand core of the strand which is as hot as possible, it is provided according to a preferred embodiment of the system according to the invention that a work roll axis of a first roughing stand next to the strand guide device of the roughing mill is not more than 7 m, preferably not more than 5 m the end of the strand guiding device is arranged.

According to a further preferred embodiment of the system according to the invention, it is provided that a feed end of the heating device facing the rough rolling mill is arranged at most 25 m, preferably at most 19 m, downstream of the work roll axis of the roughing stand closest to the heating device.

BRIEF DESCRIPTION OF THE FIGURES

Fig.1

eine schematische Darstellung einer erfindungsgemäßen Anlage zur kontinuierlichen oder semikontinuierlichen Herstellung von Stahlwarmband in Seitenansicht

Fig.2

eine Detaildarstellung einer Strangführungsvorrichtung der Anlage aus Fig.1 in vertikaler Schnittansicht

Fig.3

ein Abschnitt der Strangführungsvorrichtung in geschnittener Detailansicht

Fig.4

ein Prozessdiagramm eines erfindungsgemäßen Herstellungsverfahrens (Gießgeschwindigkeit / Strangdicke)

Fig.5

ein Diagramm zur Veranschaulichung des Jahresdurchsatzes einer erfindungsgemäßen Anlage in Abhängigkeit der Strangdicke (Gießgeschwindigkeit / Strangdicke)

Fig.6

ein Prozessdiagramm eines erfindungsgemäßen Herstellungsverfahrens (Zusammenhang von ZielGießgeschwindigkeiten und Ziel-Strangdicken)

The invention will now be explained in more detail with reference to an embodiment. Showing:

Fig.1

a schematic representation of an inventive system for continuous or semi-continuous production of steel hot strip in side view

Fig.2

a detailed representation of a strand guiding device of the system Fig.1 in vertical sectional view

Figure 3

a section of the strand guide device in a sectional detail view

Figure 4

a process diagram of a production method according to the invention (casting speed / strand thickness)

Figure 5

a diagram illustrating the annual throughput of a system according to the invention in Dependence of the strand thickness (casting speed / strand thickness)

Figure 6

a process diagram of a production method according to the invention (connection of target casting speeds and target strand thicknesses)

Embodiment of the invention

Fig.1 shows schematically a plant 1, by means of which a method according to the invention for the continuous or semi-continuous production of steel hot strip is feasible.

A vertical casting plant with a mold 2, in which strands 3 are cast, which have a strand thickness d between 105 and 130 mm, preferably a strand thickness d between 115 and 125 mm at the end of the mold 2, is apparent.

The mold 2 is preceded by a pan 35, which feeds a distributor 36 with liquid steel via a ceramic inlet nozzle. The distributor 36 subsequently charges the mold 2, to which a strand guiding device 6 adjoins.

Then the rough rolling takes place in a rough rolling 4, which may consist of a - as here - or of several scaffolds and in which the strand 3 is rolled to an intermediate thickness. During roughing, the transformation of cast structures into fine-grained rolling structures takes place.

Annex 1 also includes a series of in Fig.1 not shown components such as descaling 37,38 and in Fig.1 Separation devices, not shown, which essentially correspond to the prior art and therefore on which Place not discussed. The severing devices, for example in the form of high-speed shears, can be arranged at any position of the plant 1, in particular between the rough rolling mill 4 and the finishing train 5 and / or in a downstream region of the finishing train 5.

Behind the rough rolling 4 a heating device 7 for the intermediate band 3 'is arranged. The heater 7 is designed in the present embodiment as an induction furnace. Preferably, a transverse field heating induction furnace is used, which makes the system 1 particularly energy efficient.

Alternatively, the heater 7 could also be used as a conventional oven e.g. be executed with flame exposure.

In the heating device 7, the intermediate band 3 'is brought relatively uniformly over the cross section to a desired inlet temperature for the inlet to the finishing train 5, wherein the inlet temperature usually depending on the steel grade and subsequent rolling in the finishing train 5 between 1000 ° C and 1200 ° C is.

Behind the heating in the heating device 7 takes place - after an intermediate optional descaling-finish rolling in the multi-stand finishing train 5 to a desired final thickness and Endwalztemperatur and then a belt cooling in a cooling section 18 and ultimately a winding to frets by means of underfloor 19.

• Zunächst wird mit einer Gießanlage 2 (in den Figuren 1-3 ist eine Kokille der Gießanlage dargestellt) ein Strang 3 gegossen. Der Strang 3 wird im Liquid-Core-Reduction (LCR-) Verfahren mittels der Strangführungsvorrichtung 6 bei flüssigem Querschnittskern auf eine Strangdicke d zwischen 85 und 120 mm, vorzugsweise auf eine Strangdicke zwischen 95 und 115 mm reduziert.

According to the invention, the following method steps are carried out:

• First, with a casting plant 2 (in the Figures 1-3 is a mold of the casting plant shown) a strand 3 poured. The strand 3 is reduced in the liquid core reduction (LCR) process by means of the strand guiding device 6 with liquid cross-sectional core to a strand thickness d between 85 and 120 mm, preferably to a strand thickness between 95 and 115 mm.

A strand support length L measured between the meniscus 13, ie the casting mirror of the caster 2 and one of the roughing train 4, 14 is greater than or equal to 18.5 m, preferably the strand support length L is in a range between 18.7 (even better 20.1) and 23 m. A casting speed v _{c of} the strand 3 measured during stationary continuous operation of the system is in a range of 3.8-7 m / min.

The in Figure 3 Meniscus 13, which can be seen in detail, is usually located a few centimeters below the upper edge 34 of the mold 2, which is usually made of copper.

The strand support length L is in this case between the meniscus 13 of the mold or the caster 2 and the axis of the last, a Vorwalzstraße 4 facing roller one and described in more detail below upper guide elements series 10 measured (considered in a side view of Appendix 1 to the Axes of the roles parallel viewing direction according to Fig.1 ). In the case of an exact measurement, the strand support length L is measured at an outer broad side of the strand 3 or the strand guiding device 6 (and a section of the interior of the mold 2) opposite the center of the radius of curvature of the strand 3 or the strand guiding device 6. For better recognizability of the tangential from support rollers 10 outer broad side of the strand 3 and the strand support length L is in Fig.2 a concentric to the strand support length L auxiliary dimension line L 'located.

• bei Gießgeschwindigkeiten zwischen 3,8 und 5,0 m/min mit 100 - 120 mm Strangdicke, vorzugsweise mit 110 bis 120 mm Strangdicke,
• bei Gießgeschwindigkeiten zwischen 5,0 und 5,9 m/min mit 85
• 110 mm Strangdicke, vorzugsweise mit 95 bis 110 mm Strangdicke,
• bei Gießgeschwindigkeiten größer oder gleich 5,9 m/min mit maximal 102 mm Strangdicke.

To ensure that an initially defined swamp tip of the strand 3 regardless of respective material quality dependent maximum casting speeds always comes close to near the end of the strand guide device 6 and thereby the strand 3 with relatively little energy and while ensuring high manufacturing quality to a desired intermediate thickness before and after can also be finish rolled, strands 3 are cast with different strand thicknesses d as a function of the following casting speeds:

• at casting speeds between 3.8 and 5.0 m / min with 100-120 mm strand thickness, preferably with 110-120 mm strand thickness,
• at casting speeds between 5.0 and 5.9 m / min with 85
• 110 mm strand thickness, preferably with 95 to 110 mm strand thickness,
• at casting speeds of greater than or equal to 5.9 m / min with a maximum of 102 mm strand thickness.

In the roughing mill 4, a preliminary rolling of the strand 3 to an intermediate strip 3 'in at least four rolling passes, ie using four roughing stands 4 ₁ , 4 ₂ , 4 ₃ , 4 ₄ , preferably in five rolling passes, ie using five roughing stands. 4 ₁ , 4 ₂ , 4 ₃ , 4 ₄ , 4 ₅ takes place.

The four or five rolling passes taking place in the rough rolling mill 4 take place within a maximum of 80 seconds, preferably within a maximum of 5 seconds.

Furthermore, it is provided that the first rolling pass in the rough rolling mill 4 within a maximum of 7 minutes, preferably within a maximum of 6.2 minutes from Start of solidification of located in the caster 2 liquid extruded steel takes place. Ideally, the first rolling pass in the roughing mill 4 takes place within a maximum of 5.8 minutes, even at casting speeds in the region of 4 m / min.

Between the end 14 of the strand guide device 6 and an inlet region of the roughing train 4, only a conditional by an ambient temperature cooling of the strand 3 is allowed, i. there is no artificial cooling of the strand 3 by means of a cooling device. The surface of the strand 3 has in this area on average a temperature> 1050 ° C, preferably> 1000 ° C on.

Between the end 14 of the strand guide device 6 and the first roughing stand 4 ₁ a preferably hinged thermal cover is provided to hold the heat as possible in the strand 3. The thermal cover surrounds a conveying device provided for transporting the strand 3, usually designed as a roller belt, at least in sections. Immediately before the underfloor reel 19, the end band 3 "clamped between driving rollers 38, which also lead the end band" and keep under strip tension.

In this case, the thermal cover can surround the conveying device from above and / or from below and / or laterally.

In the roughing mill 4 per roll pass, a reduction of the thickness of the strand 3 by 35-60%, preferably by 40-55%. With a provision of exactly four roll stands, it follows that an intermediate strip 3 'with a thickness of 3 to 15 mm, preferably with a thickness of 4 to 10 mm, leaves the rough rolling line 4.

At least during the first two rolling passes the presence of a strand core as hot as possible To ensure strand 3, the next to the strand guide device 6 next adjacent first roughing stand 4 _{1 of} the roughing mill a maximum of 6 m, preferably a maximum of 5, ideally not more than 4 m after the end 14 of the strand guide device 6. The abovementioned distances are in each case measured from the center of the first roughing stand 4 ₁ or from the work roll axis thereof.

According to a further preferred process-technical variant, it is provided that a cooling of the exiting from the roughing 4 intermediate belt 3 'at a cooling rate of a maximum of 3 K / m, preferably at a cooling rate of not more than 2.5 K / m. Such a cooling rate is effected by heat radiation and / or convection from the intermediate band and can be controlled by a suitable choice of the thermal boundary conditions (covers, tunnels, cold air, air humidity, etc.) and transport speed or mass flow.

According to a preferred embodiment of the invention, provision is made for heating the intermediate strip 3 'emerging from the roughing train 4 by means of an inductive heating device 7, preferably in the transverse field heating method, starting at a temperature above 770 ° C., preferably above 820 ° C. preferably: above 950 ° C, to a temperature of at least 1110 ° C, preferably to a temperature of above 1170 ° C takes place.

The heating of the intermediate strip 3 'takes place within a period of 4 to 25 seconds, preferably within a period of 5 to 13 seconds.

When exactly four rolling passes are made in the rough rolling mill 4, it is provided that a strand 3 which is 100 mm thick when it leaves the casting plant 2 or enters the strand guiding device 6, which in the rough rolling mill 4 becomes an intermediate strip 3 'with a thickness of 7 mm is reduced after 360 seconds at the latest, preferably after 340 seconds at the latest from the casting plant 2 is introduced into the inductive heating device 7 and that at exit from the casting plant 2 or when entering the strand guiding device 6 115 mm thick strand third which is reduced in the pre-rolling line 4 to an intermediate strip 3 'with a thickness of 7.8 mm, at the latest after 480 seconds, preferably after 460 seconds from the exit from the caster 2 into the inductive heating device 7 is introduced.

A finish rolling of the heated intermediate strip 3 'in the finishing train 5 is preferably carried out in four rolling passes, ie using four finishing stands 5 ₁ , 5 ₂ , 5 ₃ , 5 ₄ or in five rolling passes, ie using five finishing stands 5 ₁ , 5 _second , 5 ₃ , 5 ₄ , 5 ₅ to an end band 3 "having a thickness of <1.5 mm, preferably <1.2 mm. Rolling to final thicknesses of <1 mm is also possible by means of a method according to the invention.

The finishing mills 5 ₁ , 5 ₂ , 5 ₃ , 5 ₄ , 5 ₅ are each arranged at intervals of <7 m, preferably at intervals of <5 m from each other (measured between the work roll axes of the finishing mills 5 ₁ , 5 ₂ , 5 ₃ , 5 ₄ , 5 ₅ ).

Subsequently, the end strip 3 "is cooled to a reeling temperature between 500 ° C. and 750 ° C., preferably to 550 ° C. and 650 ° C., and wound up into a bundle of the intermediate band 3 'or of the strand 3 in a direction transverse to the direction of transport 15 and a ready direction of the rolling mill side loose end band 3'. As an alternative to coiling, a deflection and stacking of the end strip 3 "would also be possible.

As in Fig.2 can be seen, the strand guiding device 6 comprises a plurality of predetermined for the passage of the strand 3 guide segments 16 according to Figure 3 , each one of (in Figure 3 not shown) lower series of guide elements 9 and a parallel or converging arranged upper series of guide elements 10 are constituted.

Each guide element of the lower guide element series 9 is assigned to an opposite guide element of the upper guide element series 10. The guide elements are thus arranged in pairs on both sides of the broad sides of the strand 3.

Between the two guide elements series 9, 10 a receiving shaft 11 provided for receiving a strand 2 emerging from the casting installation 2 is formed, which is at least partially tapered by forming different distances between opposing guide elements 9, 10 in the transport direction of the strand 3 and thereby the strand 3 thickness reducible. The guide elements 9, 10 are designed as rotatably mounted rollers.

As in Fig.2 As can be seen, the upper and lower guide element or roller series 9, 10 can each be in turn subdivided into (sub-) series of specific rollers with different diameters and / or axial distances.

The guide elements of the upper guide elements series 10 are selectively depth adjustable or can be connected to the Guide elements of the lower guide elements series 9 can be approximated. An adjustment of the guide elements of the upper guide elements series 10 and thus a change of the clear receiving cross section 12 of the strand guiding device 6 can be done for example by means of a hydraulic drive. One of the desired strand thickness d corresponding and measured between opposing upper and lower guide elements clear receiving width 12 of the receiving shaft 11 of the strand guide device 6, for example, could be reduced from 115 mm to a range between 90 and 105 mm.

Since a guided in a narrower receiving shaft 11 strand 3 solidifies and cools faster, the casting speed and equivalent to the rolling lines 4, 5 continuous flow should be increased if you want to continue to bring the bottom of the strand strand as close as possible to the end of the strand guide device 6.

To reduce the thickness of the strand 3, e.g. three to eight guide elements (pairs) of one of the mold 2 facing - but not necessarily adjoining the mold 2 - first guide segment 16 'adjustable. Alternatively, several juxtaposed guide segments 16 can be used for LCR thickness reduction, which connect directly or indirectly to the mold.

The strand thickness d or the light receiving width 12 can be set as a function of the material of the strand 3 and / or as a function of the casting speed.

The adjustment of the respective guide elements 9, 10 takes place in a direction substantially orthogonal to the transport direction of the strand extending direction, wherein both the upper Guide elements 10 and the lower guide elements 9 can be adjustable. As in Figure 3 can be seen, upper guide elements 10 are hinged to corresponding support members 17, which are preferably hydraulically adjustable.

The adjustable guide elements 9, 10 are preferably arranged in a front half of the casting installation 2, preferably in a front quarter of the longitudinal extension of the strand guiding device 6 facing the casting installation 2.

The setting of the strand thickness d or the clear receiving width 12 can be quasi-static, ie once, shortly after casting start, as soon as one of the Vorwalzstraße 4 facing head portion of the cast strand 3 reaches the end of the strand guide device 6 or has passed the LCR guide elements, or dynamically, ie during the casting process or during the continuous quasi-stationary passage of the strand 3 by the strand guiding device 6. In the dynamic setting of the strand thickness d this is as often as possible during the passage of a strand 3 through the strand guiding device 6, using a bottom based on Figure 6 explained relationship as a guideline, changed.

Figure 4 shows a process diagram for illustrating the manufacturing method according to the invention. On the basis of this illustration, it can be seen why, according to the invention, desired high production capacities can be achieved in generic systems for the production of steel hot-rolled strip only if the casting parameters proposed according to the invention are met, namely compared to known strand thicknesses and large metallurgical or strand support lengths L compared to known methods.

On the ordinate of the diagram according to Figure 4 the casting speed is plotted in units of [m / min], while the abscissa indicates the strand thickness in units of [mm]. Approximately parabolic lines 20a, 20b, 21a, 21b, 22a, 22b, 23a, 23b, 24a and 24b are shown, each of which corresponds to a casting characteristic for a given metallurgical or strand support length L.

In this case, several lines are shown in each case for selected strand support lengths L, since different grades of steel can be cooled at different speeds and have different solidification rates.

The lines 20a and 20b correspond to a strand support length L of 15.2 m, wherein line 20a is based on a different material-specific (global) solidification factor k than line 20b, and these two related lines therefore differ from one another.

The solidification factor k has the unit [mm / √min] and is between 24-27 mm / √min, preferably between 25 and 26 mm / √min, for materially relevant steel grades.

The lines 21a and 21b correspond to a strand support length L. of 17.5 m, wherein the lines 21a and 21b are again based on a different solidification factor k analogous to the lines 20a and 20b.

Lines 22a and 22b correspond to a preferred strand support length L of 18.5 m according to the invention and again differ only in terms of a specific solidification factor k.

The lines 23a and 23b correspond to a particularly preferred strand support length L of 20 m and according to the invention differ again with respect to a specific solidification factor k.

The lines 24a and 24b correspond to a particularly preferred strand support length L of 21.6 m according to the invention and also differ with respect to a specific solidification factor k.

Due to the problem of the sump tip position of the strand 3 already explained, it is understood that the shorter the casting length L of a respective installation, the shorter is the strand support length L (a transporting direction over the end 14 of the strand guiding device 6 out migrating Sumpfspitze would lead to a bursting of the strand 3 ').

Conversely, from the diagram according to Figure 4 be read out, which required strand thickness you have to choose in an optimized casting process, if you want to pour with a desired casting speed.

Cut in diagram according to Figure 4 For example, the line 24 b (L = 21.6 m) by means of a vertical line at a strand length of 110 mm and migrates from the obtained intersection point to the left on the ordinate, we obtain a permissible casting speed of just above 5 m / min.

The casting characteristics according to Figure 4 are purely exemplary chosen and not restrictive to understand. In principle, there is no fixed speed value for each strand thickness, but always a corresponding velocity range (and vice versa) under which the casting process can be reasonably conducted (in FIG Figure 4 with "inventional area"). Likewise, the strand support length L is not to be reduced to a certain value such as 18 m, but it has been found that strand support lengths L, which are greater than 17.5 m (and preferably less than 23 m) already allow a significant increase in capacity over known systems.

For example, results for a strand support length L of about 22m (in the embodiment according to Figure 4 traced by lines 24a, 24b, which, however, each correspond to an exact strand support length L of 21.6), a reasonable casting speed range of 4, 2-6, 5 m / min when a strand thickness of 96-117.5 mm is poured.

Calculations have shown that e.g. at a Strandstützlänge L of 22 m (which essentially corresponds to the lines 24a and 24b), a generic system 1 for the production of jet heating belt can reach a production capacity of about 3.8 million tons per year (mtpy), compared to systems according to the State of the art means a big boost.

Figure 5 shows a diagram illustrating the annual throughput (line 25), the casting speed (line 26) and the width-specific volume flow (line 27) as a function of the plotted on the abscissa strand thickness (at a strand width of 1880 mm).

Figure 6 illustrates the relationship of the strand thickness d with the casting speed v _c , wherein an adjustment of (target) casting speeds v _c or (target) strand thickness d can be determined using speed factors K proposed according to the invention. The relationship between the setting of the strand thickness d in connection with the casting speed v _c is established according to the formula stored in a device: v _c = [K_lowerLimit ... K_upperLimit] / d ² .

The following information refers to a stationary continuous operation of the system, including in the present Connection operating phases are understood with a period> 10 minutes, during which the casting speed v _c (in contrast to, for example, a Angießphase) remains substantially constant.

The choice of the speed factor K in addition to the strand support length L in particular depends on the C content of the cast steels or on their cooling characteristics. Fast-setting steel grades allow the system to operate at relatively high casting speeds v _c , while lower casting speeds v _{c are} to be selected for slower-setting steel grades in order to prevent bulging and bursting of the strand in the area of the swamp tip. The following tables refer to strands cast steel grades that are "hard" to cool, ie fast solidify and the "medium hard" to cool, ie solidify a little slower.

Corridor areas are specified for the speed factor K, within which a casting operation can be carried out efficiently and meaningfully. A strand support length-specific corridor area is limited in each case by a speed factor K_upperLimit and a speed factor K_lowerLimit according to the following tables.

The choice of the speed factor K is dependent on the strand support length L and the steel grade, in particular the carbon content of the cast steels, their solidification or conversion characteristics, their strength or ductility properties and other material characteristics dependent.

To cool the strand 3 is on this in the field of strand guiding device 6 (between the lower end of the mold 2 and the pre-rolling line 4 facing the end 14 of Strand guiding device 6) a coolant, preferably water applied. The application of the coolant to the strand 3 by means of a spraying device, not shown, which comprises any number in any configurations (eg, behind and / or next to and / or between the guide elements 9, 10) arranged spray nozzles.

For a hard cooling 3 to 4 liters of coolant per kg of extruded steel are used, for medium-hard cooling 2 to 3.5 liters of coolant per kg of extruded steel and for a soft cooling <2.5 liters (preferably 1-2.2 liters) of coolant per kg of extruded steel. The quantities of coolant called for hard, medium-hard and soft cooling overlap due to the structural design features of the spraying device and the strand guiding device 6 already mentioned above.

Under exemplary selected, substantially the same construction and boundary conditions of the sprayer and the strand guide device 6 could be about 3 liters to achieve a hard cooling 3 to 4 liters to realize a medium-hard cooling 2 to 3 liters and to realize a soft cooling 1, up to 2 liters of coolant be applied per kg of extruded steel. Table 1: Speed factor K for steel grades with low C content (<0.16%) and relatively hard cooling (3-4 liters coolant / kg extruded steel): L = 17.5 m L = 21.5 m L = 23 m K_upperLimit 48900 60300 64600 K_lowerLimit 42000 51600 55200 L = 17.5 m L = 21.5 m L = 23 m K_upperLimit 46500 57200 61900 K_lowerLimit 39600 48300 52100 L = 17.5 m L = 21.5 m L = 23 m K_upperLimit 44100 54050 59000 K_lowerLimit 37100 44800 48900

Thus, according to a preferred operation according to Table 1, it is provided that for hard-to-cool strip steels, ie by applying 3 to 4 liters of coolant per kg of extruded steel, the relationship between the strand thickness d measured in [mm] and that in [m / min] measured velocity V _c according to the formula v _c = K / d ^{2 is} maintained, wherein a speed factor K contained in the formula at a preferably minimum strand support length L _min of 17.5 m in a corridor range of 42000 to 48900, preferably in a corridor range of 45500 to 48900, while the speed factor K lies at a preferably maximum strand support length L _max of 23 m in a corridor range of 55200 to 64600, preferably in a corridor range of 59900 to 64600.

In order to determine (target) casting speeds v _c or (target) strand thicknesses d for systems having strand support lengths L between the preferred strand support lengths L _min and L _max , an interpolation between the corridor regions listed above (to obtain another, not in the tables lead corridor area) feasible. For example, for a strand support length L of 21.5 m for steel grades with a C content <0.16% and relatively hard cooling, a corridor range of 51600 to 60300 results. Interpolation between the corridor regions takes place in a substantially linear manner.

In the case of strand support lengths> L _{max, it} is also possible to extrapolate to the corridor ranges listed above.

According to Table 2, for steel grades with a C content> 0.16% and medium-hard cooling, it is recommended to use a speed factor K with a strand support length L of 17.5 m from a corridor range of 39600 to 46500 and at a strand support length L of 21.5 m from a corridor range of 48300 to 57200 and at a strand support length L of 23 m from a corridor range of 52100 to 61900.

According to Table 3, it is recommended for mild steel grades to be cooled, i. by applying 1 to 2.5 liters of coolant per kg of strand steel, taking a speed factor K at a strand support length L of 17.5 m from a corridor range of 37100 to 44100 and at a strand support length L of 21.5 m from a corridor range of 44800 to 54050 and at a strand support length L of 23 m from a corridor range of 48900 to 59000.

Figure 6 shows a diagram with corresponding to the above-mentioned speed factors K curves 28-33. On the abscissa of the diagram, the strand thickness d (measured at the end of the strand guiding device 6 or when entering the rough rolling mill 4) is plotted in the unit [mm], the ordinate represents the casting speed in the unit [m / min].

The characteristic curves 28, 29 and 30 apply to strand support lengths L = 17.5 m, the characteristic curves 31, 32 and 33 for strand support lengths L = 21.5 m.

Decisive for an efficient operation of the plant are each the highest, for a specific strand support length L valid curves, thus according to Figure 6 for strand support lengths L = 17.5 m the characteristic curve 28 and for strand support lengths L = 21.5 m the characteristic curve 31.

The uppermost characteristic curves for a specific strand support length L correspond to the speed factors K_upperLimit listed above in tabular form. Specifically, characteristic 28 corresponds to one Speed factor K of 48900 and characteristic 31 a speed factor K of 60300. The curves 28 and 31 thus correspond to rapidly solidifying steel grades, which allow high casting speed and heat dissipation in compliance with standardized quality criteria.

The according to Figure 6 lowest characteristic curves valid for a specific strand support length L (for strand support lengths L = 17.5 m: characteristic curve 30; for strand support lengths L = 21.5 m: characteristic curve 33) correspond to the speed factors K_lowerLimit tabular.

The grades 32 and 33 corresponding steel grades are not so "hard" due to their slower solidification, i. not as quickly coolable as a grade 31 corresponding steel grade. Likewise, the grades 29 and 30 corresponding steel grades are not as cool as a corresponding characteristic 28 steel grade.

The cooling speed determines significantly the position of the sump tip within the strand 3. Above the steel-grade specific curves 28-31 lying casting speed ranges are to be avoided in order to prevent bulging and bursting of the strand 3 in the area of the sump tip. In other words, the curves 28-31 represent limit casting speed curves for different grades of steel.

At an in Figure 6 with the starting point of an arrow 31 'identical management with a casting speed v _c = 6.5 m / min and a strand thickness d = 104.5 mm would be, for example, the bottom of the strand 3 strand at the end of the strand guide device 6, ie as close as possible to the entry into the Vorwalzstraße 4, whereby an optimal use of the Casting heat is ensured for the subsequent rolling process. If, as shown by way of example by arrow 31 ', the casting speed v _{c is} reduced to 5 m / min for operational reasons, the strand thickness d would have to be raised to approximately 110 mm in accordance with arrow 31 "in order to keep the sump tip of the strand 3 on To keep the end of the strand guide device 6 and to ensure optimum utilization of the casting heat for subsequent rolling process.

Conversely, when the casting speed v _{c is increased} (eg after operational problems which necessitated temporary throttling of the casting speed v _{c have} been eliminated), the strand thickness d must be correspondingly reduced.

In the case of operational reasons, which necessitate a reduction in the casting speed v _c , these may be, for example, irregularities in the area of the slide or mold, in particular at the bath level of the mold or deviations in the line temperature from predetermined values, detected by sensors.

A change in the strand thickness d can be effected by a previously described dynamic LCR thickness reduction by means of the LCR guide segment 16 '.

If the casting speed v _c falls down from the above-mentioned relationships, the operating team is notified by an output device in order to reduce the liquid core reduction (LCR) so that the strand thickness d increases, and so the context of the invention or a respective Corridor area to reach again. In accordance with the invention, it is preferable to aim for an upper region of the corridor. Depending on what is considered by the operators as the main parameter of the system (the strand thickness d or the casting speed v _c ), starting from a desired strand thickness d, a corresponding target casting speed v _c can be selected or, starting from a desired casting speed v _c the strand thickness d be varied accordingly.

It should be noted that changes in the strand thickness d described above in terms of high operational stability are only carried out with relevant changes in the casting speed v _c (eg changes of v _c by approx. 0.25 m / min) and not with every minor deviation Casting speed v _c from a respective desired target casting speed.

Based on the characteristic curves according to the invention or on the corresponding speed factors K, the strand thickness d can be increased as the casting speed v _c decreases, thereby increasing the material throughput and thus optimizing it.

Since a casting speed v _c above about 7 m / min are hardly accessible for stable casting, this range has been determined from the diagram of FIG Figure 6 hidden.

Claims (26)

1. Method for continuous or semi-continuous production of hot steel strip which, starting from a slab (3) guided through a slab-guiding device (6), is rolled in a roughing train (4) to an intermediate strip (3') and in a further sequence in a finish rolling train (5) is rolled to a final strip (3"), characterised in that a slab (3) cast in a die (2) of a casting plant has a slab thickness (d) of between 105 and 130 mm, preferably a slab thickness (d) of between 115 and 125 mm, and is reduced in a Liquid Core Reduction (LCR) process by means of the subsequent slab-guiding device (6) with a liquid cross-sectional core of the slab (3) to a slab thickness (d) of between 95 and 120 mm, preferably to a slab thickness (d) of between 95 and 115 mm, wherein a slab support length (L) measured between the meniscus (13), i.e. the bath level of the die (2) and an end (14) of the slab-guiding device (6) facing the roughing train (4), amounts to greater than or equal to 18.5 m, preferably lies in a range between 18.7 and 23 m, especially preferably between 20.1 and 23 m,
   wherein a casting velocity (v_c) lies in a range of 3.8 - 7 m/min and slabs (3) with different slab thicknesses (d) are cast as a function of the following casting velocities:

   - for casting velocities between 3.8 and 5.0 m/min with 100 - 120 mm slab thickness, preferably with 110 to 120 mm slab thickness,

   - for casting velocities between 5.0 and 5.9 m/min with 85 - 110 mm slab thickness, preferably with 95 to 110 mm slab thickness,

   - for casting velocities greater than or equal to 5.9 m/min with maximum 102 mm slab thickness, and

   wherein, in the roughing train (4) a rough rolling of the slab (3) into an intermediate slab (3') is undertaken within a period of at most 80 seconds, preferably within at most 50 seconds, and this is done in at least four rolling passes, i.e. using four roughing stands (4₁, 4₂, 4₃, 4₄), preferably in five rolling passes, i.e. using five roughing stands (4₁, 4₂, 4₃, 4₄, 4₅).
2. Method according to claim 1, characterised in that the first rolling pass in the roughing train (4) occurs within at most 7 minutes, preferably within at most 6.2 minutes from the start of solidification of the liquid slab (3) present in the die (2).
3. Method according to one of claims 1 or 2, characterised in that, between the end (14) of the slab-guiding device (6) and an entry area of the roughing train (4) only cooling of the slab (3) resulting from an ambient temperature is allowed.
4. Method according to one of claims 1 to 3, characterised in that in the roughing train (4) there is a reduction of the thickness of the slab (3) by 35-60%, preferably by 40-55% per rolling pass.
5. Method according to one of claims 1 to 4, characterised in that the intermediate strip (3') emerging from the roughing train (4) is cooled at a cooling rate of a maximum of 3 K/m, preferably at a cooling rate of a maximum of 2.5 K/m.
6. Method according to one of claims 1 to 5, characterised in that the intermediate strip (3') emerging from the roughing train (4) is heated by means of an inductive heating device (7), preferably using the cross-field heating method, starting at a temperature above 770°C, preferably above 820°C, to a temperature of at least 1110°C, preferably to a temperature of above 1170°C.
7. Method according to claim 6, characterised in that the intermediate strip (3') is heated up within a period of 4 to 25 seconds, preferably within a period of 5 to 13 seconds.
8. Method according to claim 1 and 6, characterised in that, when precisely four rolling passes are performed in the roughing train (4), there is provision for the elapsed time between the first rolling pass and the entry into the heating device (7), for intermediate strip thicknesses of 5-10 mm, not to amount to longer than 105 seconds, preferably not longer than 70 seconds.
9. Method according to one of claims 1 to 8, characterised in that the heated intermediate strip (3') is finished in the finish rolling train (5) in four rolling passes, i.e. using four finishing stands (5₁, 5₂, 5₃, 5₄) or in five rolling passes, i.e. using five finishing stands (5₁, 5₂, 5₃, 5₄, 5₅) to a final strip (3") with a thickness < 1.5 mm, preferably < 1.2 mm.
10. Method according to claim 9, characterised in that the rolling passes carried out within the finish rolling train (5) occur within a period of a maximum of 16 seconds, preferably within a period of a maximum of 8 seconds.
11. Method according to one of claims 1 to 10, characterised in that, for LCR thickness reduction of the slab (3), predefined guide elements (9, 10) of the slab-guiding device (6) are adjustable relative to the longitudinal axis of the slab (3) for making contact with the slab, wherein the guide elements (9, 10) are adjusted as a function of the material of the slab (3) and/or of the casting velocity (v_c).
12. Method according to claim 11, characterised in that the slab thickness (d) is able to be adjusted quasi-statically after the beginning of a casting sequence, i.e. shortly after the slab (3) emerges from the die (2).
13. Method according to claim 11, characterised in that the slab width (d) is dynamically adjustable, i.e. able to be varied by any given amount during the casting process or during the passage of the slab (3) through the slab-guiding device (6).
14. Method according to one of claims 1 to 13, characterised in that for hard-to-cool slab steels by means of a spray device in the area of the slab-guiding device (6), i.e. by applying 3 to 4 litres of coolant per kg of slab steel, in a stationary-continuous operation of the plant, the relationship of a slab thickness (d) measured in [mm] to the casting velocity (v_c) measured in [m/min] is adhered to in accordance with the formula v_c= K / d², wherein a speed factor (K) contained in the formula for a slab support length (L)=17.5 m lies in the corridor range of 42000 to 48900, preferably in a corridor range of 45500 to 48900, while the speed factor (K) for a slab support length (L)=23 m lies in a corridor range of 55200 to 64600, preferably in a corridor range of 59900 to 64600, wherein to determine (target) casting velocities (v_c) or (target) slab thicknesses (d), for plants with slab support lengths (L) lying between the slab support lengths L=17.5 m and L=23 m, an interpolation between the previously listed corridor ranges is able to be carried out.
15. Method according to one of claims 1 to 13, characterised in that, for slab steels that are medium-hard to cool by means of a spray device in the area of the slab-guiding device (6), i.e. by application of 2 to 3.5 litres of coolant per kg of slab steel, in a stationary-continuous operation of the plant, the relationship of a slab thickness (d) measured in [mm] to the casting velocity (v_c) measured in [m/min] is adhered to in accordance with the formula v_c= K / d², wherein a speed factor (K) contained in the formula for a slab support length (L)=17.5 m lies in a corridor range of 39600 to 46500, preferably in a corridor range of 43050 to 46500, while the speed factor (K) for a slab support length (L)=23 m lies in a corridor range of 52100 to 61900, preferably in a corridor range of 57000 to 61900, wherein for determining (target) casting velocities (v_c) or (target) slab thicknesses (d) for plants with slab support lengths (L) lying between the slab support lengths L=17.5 m and L=23 m, an interpolation between the previously listed corridor ranges is able to be carried out.
16. Method according to one of claims 1 to 13, characterised in that for soft slab steels to be cooled in the area of the slab-guiding device (6), i.e. by application of less than 2.2 litres of coolant per kg of slab steel, in a stationary-continuous operation of the plant, the relationship of a slab thickness (d) measured in [mm] to the casting velocity (v_c) measured in [m/min] is adhered to in accordance with the formula v_c= K / d², wherein a speed factor (K) contained in the formula for a slab support length (L)=17.5 m lies in a corridor range of 37100 to 44100, preferably in a corridor range of 40600 to 44100, while the speed factor (K) for a slab support length (L)=23 m lies in a corridor range of 48900 to 59000, preferably in a corridor range of 53950 to 59000, wherein for determining (target) casting velocities (v_c) or (target) slab thicknesses (d) for plants with slab support lengths (L) lying between the slab support lengths L=17.5 m and L=23 m, an interpolation between the previously listed corridor ranges is able to be carried out.
17. Plant for carrying out a method for continuous or semi-continuous production of hot steel strip according to one of claims 1 to 16, comprising a die (2), a slab-guiding device (6) downstream thereof, a roughing train (4) downstream thereof, a preferably inductive heating device (7) downstream thereof and a finish rolling train (5) downstream thereof, wherein the slab-guiding device (6) has a series of lower guide elements (9) and a series of upper guide elements (10) disposed in parallel or converging therewith and between the two guide element series (9, 10) a receiving shaft (11) provided for receiving a slab (3) emerging from the die (2) is embodied, which by embodying different distances between opposing guide elements (9, 10) to one another in the transport direction of the slab (3), is narrowed at least in sections and through this the slab (3) is able to be reduced in thickness, characterised in that the clear receiving width (12) of the receiving shaft (11) at its input area pointing towards the die (2), amounts to between 105 and 130 mm, preferably between 115 and 125 mm, that the receiving shaft (11) at its end (14) pointing towards the roughing train (4) has a clear receiving width (12) corresponding to the slab thickness (d) of the slab (3) of between 95 and 120 mm, preferably of between 95 and 115 mm, wherein a slab support length (L) measured between the meniscus (13), i.e. the bath level of the die and the end (14) of the receiving shaft (11) of the slab-guiding device (6) facing towards the roughing train (4) is greater than or equal to 18.5 m, preferably lies in a range between 18.7 and 23 m, especially preferably between 20.1 and 23 m, and wherein a control device is provided, by means of which the casting velocity (v_c) of the slab (3) is able to be kept in a range between 3.8 - 7 m/min, and that the roughing train (4) comprises four or five roughing stands (4₁, 4₂, 4₃, 4₄, 4₅).
18. Plant according to claim 17, characterised in that no cooling device is provided between the end (14) of the receiving shaft (11) or of the slab-guiding device (6) and a feed area of the roughing train (4), but a thermal cover is provided, which at least surrounds sections of a conveyor device for the transport of the slab (3).
19. Plant according to one of claims 17 to 18, characterised in that, by means of roughing stands (4₁, 4₂, 4₃, 4₄, 4₅) disposed in the roughing train (4), a reduction of the thickness of the slab (3) by respectively 35-60%, preferably by respectively 40-55% per roughing stand (4₁, 4₂, 4₃, 4₄, 4₅) is able to be undertaken so that an intermediate strip (3') with a thickness of 3 to 15 mm, preferably with a thickness of 4 to 10 mm, is able to be created.
20. Plant according to one of claims 17 to 19, characterised in that the heating device (7) is embodied as an inductive cross-field heating oven, by means of which the slab (3), starting at a temperature of above 770°C, preferably of above 820°C, is able to be heated up to a temperature of at least 1110°C, preferably to a temperature of above 1170°C.
21. Plant according to one of claims 17 to 20, characterised in that the finish rolling train (5) comprises four finishing stands (5₁, 5₂, 5₃, 5₄) or five finishing stands (5₁, 5₂, 5₃, 5₄ 5₅), by means of which an intermediate strip (3') emerging from the roughing train (4) is able to be reduced to a final strip (3") with a thickness < 1.5 mm, preferably < 1.2 mm.
22. Plant according to claim 21, characterised in that the finishing stands (5₁, 5₂, 5₃, 5₄, 5₅) are each disposed at distances of < 7 m, preferably at distances of < 5 m from one another, wherein the distances are measured between the working roller axes of the finishing stands (5₁, 5₂, 5₃, 5₄, 5₅).
23. Plant according to one of claims 17 to 22, characterised in that, for reducing the thickness of the slab (3), specific guide elements (9, 10) are adjustable and through this a clear receiving width (12) of the receiving shaft (11) is able to be reduced or enlarged, wherein the slab thickness (d) or the clear receiving width (12) is able to be adjusted as a function of the material of the slab and/or of the casting velocity.
24. Plant according to claim 23, characterised in that the adjustable guide elements (9, 10) are disposed in a front half, preferably in a front quarter, of the longitudinal extent of the slab-guiding device (6) facing towards the die (2).
25. Plant according to one of claims 17 to 24, characterised in that a working roller axis of the first roughing stand (4₁) of the roughing train (4) closest to the slab-guiding device (6) is disposed at a maximum of 7 m, preferably at a maximum of 5 m after the end (14) of the slab-guiding device (6).
26. Plant according to one of claims 17 to 25, characterised in that an entry end (7a) of the heating device (7) facing towards the roughing train, is disposed at a maximum of 25 m, preferably at a maximum of 19 m after the operating roller axis of the roughing stand closest to the heating device (7).

Images