Apparatus and method for producing a hot-rolled metal strip

Abstract

An apparatus (1) and a method for producing a hot-rolled metal strip (2), wherein the apparatus (1) has: a finishing train (10), with at least one roll stand (11), which has work rolls forming a roll gap, for hot-rolling the metal strip (2); and a quick-cooling device (20), which is directly downstream of the roll gap of the last roll stand (11) of the finishing train (10) and is configured to cool the metal strip (2) quickly by applying a coolant, preferably a water-based coolant, to the upper side and the underside of the metal strip (2) along a cooling zone of the quick-cooling device (20); wherein the quick-cooling device (20) is configured to apply coolant both to the upper side and to the underside of the metal strip (2) at a rate of between 100 and 300 m3 / (m2*h).

Description

[0001] Apparatus and method for producing a hot-rolled metal strip

[0002] Technical area

[0003] The invention relates to an apparatus and a method for producing a hot-rolled metal strip, comprising a finishing train for hot-rolling the metal strip and a cooling device for cooling the metal strip downstream of the finishing train.

[0004] Background of the invention

[0005] A general optimization goal for rolling a metal strip in a rolling mill, especially a hot strip mill, is to optimize the strength and toughness properties of the material and avoid stresses. For this purpose, the cooling of the hot-rolled products following forming can be specifically influenced.

[0006] It is known that a fine grain structure (fine grain hardening) has a positive effect on the strength and toughness properties of the material. According to the Hall-Petch and Cottrell-Petch relationships, a decrease in the fine grain size in the material's microstructure leads to an increase in strength and toughness. Generally, a decrease in the ferrite grain diameter leads to an increase in the yield strength and tensile strength; see also WO 2014 / 177664 A1.

[0007] With the conventional thermomechanical rolling and cooling process, it is difficult to achieve a fine grain size of less than 5 pm. Therefore, concepts in plant, process, and engineering for the production of high-strength metallic materials on an industrial scale continue to be the subject of research and development. i Description of the invention

[0008] An object of the invention is to provide an improved apparatus and an improved method for producing a hot-rolled metal strip, in particular to improve the mechanical properties of the metal strip.

[0009] This object is achieved by a device having the features of claim 1 and a method having the features of the subordinate method claim. Advantageous further developments follow from the subclaims, the following description of the invention, and the description of preferred embodiments.

[0010] The device is used for hot rolling a metal strip, for example, with a final rolling temperature of approximately 850 °C. The device is particularly used in hot rolling mills, including CSP plants or heavy plate rolling mills. The rolled product to be processed is a metal strip, preferably a steel strip, which, as a general term, includes flat rolled products such as sheets of various qualities.

[0011] The device comprises a finishing train with at least one rolling stand, which conventionally comprises work rolls forming a roll gap, for hot rolling the metal strip. The metal strip is transported in a conveying direction during rolling and leaves the last rolling stand in the conveying direction.

[0012] The device further comprises a rapid cooling device, which is arranged directly behind the roll gap of the last rolling stand of the finishing train and is configured to rapidly cool the metal strip by applying a coolant to the top and bottom of the metal strip along a cooling section of the rapid cooling device. The coolant is preferably water or a liquid water-based coolant. The rapid cooling device can be arranged such that the cooling of the metal strip takes place at least partially within the extension of the last rolling stand in the conveying direction.

[0013] The rapid cooling device is designed according to the invention to apply a coolant quantity of between 100 and 300 m to both the top and the bottom of the metal strip. 3 / (m 2 *h) to be applied.

[0014] Such a small amount of coolant applied immediately after finish rolling reliably prevents grain growth during the austenite-to-ferrite transformation and recrystallization in the metal strip microstructure. According to the Hall-Petch and Cottrell-Petch relationships, this leads to an increase in the strength and toughness of the metal strip.

[0015] The rapid cooling device can have spray bars on the top and bottom sides relative to the metal strip, each with a plurality of nozzles for spraying the coolant onto the metal strip. The number of nozzles on the top side of the metal strip is preferably 50 to 120 nozzles / m. 2 and on the underside preferably 80 to 150 nozzles / m 2The upper nozzles are preferably positioned a maximum of 800 mm above the metal strip, and the lower nozzles are preferably positioned a maximum of 170 mm below the metal strip. The diameter of the nozzles is preferably in the range of 3 to 8 mm. Using the specified parameters, it is possible to apply a sufficient amount of coolant to the metal strip within a short cooling distance for rapid cooling.

[0016] For the same reason, the coolant pre-pressure is preferably in the range of 2 to 5 bar. For this purpose, the rapid cooling device comprises a coolant supply and one or more coolant supply lines, which are in fluid communication with the spray booms to supply the nozzles with coolant at the specified pressure, which can be achieved, for example, using a suitably high elevated tank or standpipe or using booster pumps.

[0017] In addition to applying a sufficient amount of coolant to the metal strip, it can be important to prevent the coolant from escaping uncontrollably toward the last rolling stand of the finishing train or in the opposite direction. For example, strip measuring devices can be installed directly upstream and / or downstream of the rapid cooling device, but coolant leakage should be avoided to prevent falsifying the measurement results.

[0018] To prevent uncontrolled leakage of coolant from the cooling section of the rapid cooling device, one or more end-side spray bars in the front and rear areas are preferably arranged so that the spray direction of the coolant from the corresponding nozzles is directed obliquely toward the metal strip, into the interior of the rapid cooling device. For this purpose, the end-side spray bars and / or their nozzles can be angled relative to the conveying direction of the metal strip.

[0019] To prevent uncontrolled coolant leakage from the cooling section of the rapid cooling system, a squeeze roller and / or an air blow-off device can be installed at the inlet and / or outlet of the rapid cooling system. Such measures are particularly useful on the top side of the metal strip, where coolant can collect without dripping down.

[0020] Preferably, the rapid cooling device is configured to set cooling rates for which the following applies: cooling rate * strip thickness > 500 K / s * mm, thereby achieving particularly rapid cooling of the metal strip. Preferably, the length Li of the cooling section of the rapid cooling device is at least 4 m and / or a maximum of 10 m, in particular approximately 9 m, whereby rapid cooling takes place within a comparatively short cooling section.

[0021] The rapid cooling achieved in this way is intended to prevent any tension in the metal strip, which could lead to edge waves and / or unevenness. To prevent this, the coolant quantities on the top and bottom sides of the metal strip can be set in a specific ratio. Good flatness is achieved when more coolant is applied to the underside of the metal strip than to the top. The coolant quantity ratio from top to bottom can be adjusted using a flow control, preferably separately on the top and bottom of the metal strip, in order to specifically prevent tension in the strip. The coolant quantity ratio from top to bottom can preferably be adjusted in the range of at least 3:1 to 1:3. A coolant quantity ratio between top and bottom of 1:2 is optimal.

[0022] Preferably, the rapid cooling device is designed to apply a total coolant quantity of at least 800 m 3 / h per meter of strip width, more preferably at least 1500 m 3 / h, particularly preferably at least 2400 m 3 / h.

[0023] Preferably, the device comprises a further cooling device downstream of the rapid cooling device, which is configured to adjust the metal strip to the desired final temperature, preferably a suitable coiling temperature. The further cooling device is preferably designed for laminar cooling.

[0024] The above-mentioned object is further achieved by a method for producing a hot-rolled metal strip, the method comprising: hot rolling a metal strip in a finishing train having at least one rolling stand having work rolls forming a roll gap; and immediate cooling of the metal strip following the hot rolling by applying a coolant, preferably water-based, to the top and bottom of the metal strip along a cooling section of the rapid cooling device, the rapid cooling device being arranged immediately behind the roll gap of the last rolling stand of the finishing train; the rapid cooling device applying a coolant quantity of between 100 and 300 m to both the top and bottom of the metal strip 3 / (m 2 *h) applies.

[0025] The features, technical effects, advantages and embodiments described with regard to the device apply analogously to the method.

[0026] For the reasons stated above, the rapid cooling device preferably comprises, on the top and bottom sides, relative to the metal strip, spray bars each having a plurality of nozzles for spraying the coolant onto the metal strip, a coolant supply and one or more coolant feed lines which are in fluid communication with the spray bars for supplying the nozzles with the coolant, wherein the coolant supply preferably sets the pre-pressure of the coolant in the coolant feed lines to a pressure of 2 to 5 bar.

[0027] For the reasons mentioned above, the rapid cooling device preferably has one or more end-side spray bars in the front and / or rear region of the rapid cooling device, the nozzles of which apply the coolant to the metal strip at an angle that is directed obliquely into the interior of the rapid cooling device.

[0028] For the reasons stated above, a cooling rate is preferably set in the rapid cooling device to which the following applies: cooling rate * strip thickness > 500 K / s * mm. For the reasons stated above, the underside of the metal strip is preferably exposed to at least twice as much coolant in the rapid cooling device as the top side of the metal strip.

[0029] For the reasons mentioned above, a total coolant quantity of at least 800 m is preferably applied to the top and bottom of the metal strip in the rapid cooling device. 3 / h per meter of strip width, more preferably at least 1500 m3 / h, particularly preferably at least 2400 m 3 / h.

[0030] Further advantages and features of the present invention will become apparent from the following description of preferred embodiments. The features described therein can be implemented alone or in combination with one or more of the features set forth above, provided the features do not contradict each other. The following description of preferred embodiments is provided with reference to the accompanying drawings.

[0031] Short description of the characters

[0032] Preferred further embodiments of the invention are explained in more detail in the following description of the figures. In the figures:

[0033] Figure 1 shows schematically an apparatus for producing a metal strip, comprising a finishing train and a rapid cooling device; and

[0034] Figure 2 schematically shows the rapid cooling device according to an embodiment.

[0035] Detailed Description of Preferred Embodiments Preferred embodiments are described below with reference to the figures. Identical, similar, or equivalent elements are provided with identical reference numerals in the figures, and a repeated description of these elements is partially omitted to avoid redundancy.

[0036] Figure 1 schematically shows a device 1 for producing a metal strip 2. The device 1 is used particularly in hot rolling mills, including CSP plants or heavy plate rolling mills. The rolled stock to be processed is a metal strip 2, preferably a steel strip, which, as a general term, encompasses flat rolled products such as sheets of various qualities.

[0037] The device 1 has a finishing train 10, the last rolling stand 11 of which is shown in Figure 1. The metal strip 2 is hot-rolled in the finishing train 10 and leaves the last rolling stand 11 in a conveying direction F.

[0038] Immediately behind the last rolling stand 11 of the finishing train 10, in particular behind the roll gap of the last rolling stand 11, a rapid cooling device 20 is arranged, which is designed to rapidly cool the metal strip 2 immediately after hot rolling. The rapid cooling in the rapid cooling device 20 takes place within a comparatively short cooling section with a length Li of, for example, less than 10 m, preferably approximately 9 m, measured from the roll gap of the last rolling stand 11 of the finishing train 10.

[0039] Downstream of the rapid cooling device 20, a further cooling device 30 is arranged, which is configured to adjust the metal strip 2 to the desired final temperature, for example, to a suitable coiling temperature. The further cooling device 30 can be designed for laminar cooling, in which the coolant, in particular cooling water, is applied to the rolled stock at a comparatively low line pressure (for example, between 0.05 and 0.1 bar). The cooling device 30 has a plurality of spray beams 31, which apply the coolant to the metal strip 2 from above or both from above and below, preferably in a uniform, curtain-like laminar flow.

[0040] The additional cooling device 30 can be divided into several segments or sections, for example, ten segments according to the present embodiment. The distance L2 of the additional cooling device 30 from the roll gap of the last rolling stand 11 of the finishing train 10, measured at the beginning of the cooling device 30, is preferably less than 20 m, in particular approximately 14 m.

[0041] Downstream of the further cooling device 30, a reeling device 40 for winding the finished metal strip 2 is installed.

[0042] One or more temperature gauges 50, 60 can be installed on the treatment line for the metal strip 2, for example between the rapid cooling device 20 and the further cooling device 30 and downstream of the further cooling device 30, in order to measure the temperature(s) at the corresponding locations for monitoring the process progress.

[0043] In order to achieve immediate cooling of the metal strip 2 following hot rolling in the finishing train 10, the rapid cooling device 20 combines various properties which, individually but especially in combination, make it possible to "freeze" the microstructure after the last forming in the finishing train 10 and prevent grain growth and recrystallization. During the subsequent austenite-ferrite transformation, an extremely small ferrite grain is achieved, preferably less than 5 pm. According to the Hall-Petch and Cottrell-Petch relationships, this leads to an increase in the strength and toughness of the metal strip 2. The applied deformation in the rolling stands before rapid cooling is preferably between 10 - 50%. Cooling in the rapid cooling device 20 takes place in such a way that, if possible, only an austenite-ferrite transformation occurs. If the final rolling temperature is approx.850 °C, the rapid cooling device 20 is preferably configured so that the temperature after the rapid cooling is approximately 700 °C. In a subsequent cooling in the further cooling device 30, which is connected to the rapid cooling device 20, the desired final temperature or coiling temperature can be set.

[0044] Materials whose mechanical properties are particularly improved by this instant cooling preferably have a ferritic microstructure. The chemical analysis of such materials preferably lies in the following ranges:

[0045]

[0046] Table 1: Example chemical analysis of a ferritic microstructure for metal strip 2.

[0047] 5 In order to achieve instant cooling in the rapid cooling device 20 with the above-mentioned results, the rapid cooling device 20 is designed to apply a sufficiently high amount of coolant compactly to the metal strip 2. The application is on the top and bottom sides between 100 and 300 m 3 / (m 2 *h).

[0048] ,O

[0049] The rapid cooling device 20 (see also Figure 2) has spray bars 21 on the top and bottom sides (relative to the metal strip 2), each with a plurality of nozzles 22, which are supplied with a coolant via a coolant supply 23 and one or more coolant supply lines 24. The coolant is preferably water or a liquid water-based coolant.

[0050] The coolant pre-pressure in the coolant supply lines 24 is preferably in the range of 2 to 5 bar, which can be achieved, for example, by means of a correspondingly high tank or standpipe or by means of one or more booster pumps in the coolant supply 23. The number of nozzles 22 on the top side is preferably 50 to 120 nozzles / m 2 and on the underside preferably 80 to 150 nozzles / m 2 The height of the upper spray beams 21 or nozzles 22 is preferably a maximum of 800 mm above the strip edge. The lower nozzles 22 are preferably arranged a maximum of 170 mm below the strip edge. The diameter of the nozzles 22 is preferably in the range of 3 to 8 mm.

[0051] In addition to applying a sufficient amount of coolant to the metal strip 2, it is important that the coolant does not escape uncontrollably toward the last rolling stand 11 of the finishing train 10 or in the other direction, i.e., toward the further cooling device 30. For example, strip measuring devices can be installed directly upstream and / or downstream of the rapid cooling device 20, but coolant leakage should be avoided to avoid distorting the measurement result.

[0052] To prevent uncontrolled escape of coolant from the cooling section of the rapid cooling device 20, one or more end-side spray bars 21' are arranged in the front and / or rear region such that the spray direction of the coolant from the corresponding nozzles 22' is directed obliquely into the interior of the rapid cooling device 20, see Figure 2. For this purpose, the end-side spray bars 21' and / or their nozzles 22' can be inclined relative to the conveying direction F. Further measures can be taken to prevent uncontrolled coolant escape from the rapid cooling device 20. Preferably, a coolant spray system with a pre-pressure of approximately 8 to 15 bar is installed with flat jet nozzles, which are arranged in a row preferably orthogonal to the conveying direction F. Furthermore, at least one squeeze roller 25 can be provided at the outlet of the rapid cooling device 20.An air blower 26 can be installed directly upstream of any measuring devices to completely clean the strip surface of coolant and steam. Typical air velocities at the nozzle outlet of the air blower are preferably between 200 and 750 m / s.

[0053] The coolant supply 23 and / or coolant supply lines 24 can have a bypass circuit used to switch the coolant on and off very quickly. This makes it possible to set defined head and foot lengths very precisely.

[0054] Preferably, the rapid cooling device 20 is configured to set cooling rates for which the following applies: cooling rate * strip thickness > 500 K / s * mm. The length Li of the direct cooling in the rapid cooling device 20 is preferably at least 4 m.

[0055] The rapid cooling performed in this way must prevent any tension in the metal strip 2, which could result in edge waves and / or unevenness. To achieve this, the coolant quantities on the top and bottom sides of the metal strip 2 should be set in a specific ratio. Good flatness is achieved when twice as much coolant is applied to the underside of the metal strip.

[0056] The total coolant quantity on the top and bottom of the metal strip 2 should be at least 800 m 3 / h per meter of bandwidth, preferably at least 1500 m 3 / h, particularly preferably at least 2400 m 3 / h. The coolant quantity ratio from the top side to the bottom side is preferably adjustable separately on the top and bottom sides of the metal strip 2 by means of a flow control in order to specifically prevent tension in the strip. The coolant quantity ratio from the top side to the bottom side is preferably adjustable in a range of at least 3:1 to 1:3. A coolant quantity ratio from the top side to the bottom side of 1:2 is optimal.

[0057] For different applications, the cooling in the rapid cooling device 20 should be flexible, allowing for setting lower cooling rates in addition to the highest cooling rates for other metal strips 2. For this purpose, the spray bars 21 as a whole and / or individually are preferably equipped with flow meters and flow controls, for example in the form of control valves and / or pumps. This allows a reduction of the coolant quantity to at least 30% of the maximum flow rate, preferably 20%, particularly preferably 10%.

[0058] Temperature gauges 50, 60 in the form of pyrometers can only measure surface temperatures. During rapid cooling within the rapid cooling device 20, no measurement is possible in this way. Therefore, one or more measurements in the finishing train 10 and / or after the rapid cooling, for example, using temperature gauges 50, 60, are advisable.

[0059] Since temperature measurement immediately after the last roll stand 11 of the finishing train 10 is impossible or difficult due to the immediately following rapid cooling device 20, temperature measurement is preferably carried out directly before the last roll stand 11 and / or in one of the previous roll stands. Temperature measurement at the entrance to the roll gap of the last roll stand 11 is difficult due to the ambient conditions (roll cooling, inter-stand cooling, etc.). For this reason, in addition to a pyrometer, a compressed air nozzle with a pressure of approximately 3 to 8 bar is preferably installed at a height of 200 - 600 mm relative to the metal strip 2 for temperature measurement before the rapid cooling device 20 to enable interference-free measurement.Nevertheless, the pyrometer should continue to measure at a wavelength that is insensitive to stray coolant, especially water, in order to exclude any influence of residual coolant if possible.

[0060] Preferably, the temperature distribution of the metal strip 2 in the rapid cooling is known in order to be able to adjust the required coolant quantities in the rapid cooling device 20 as precisely as possible.

[0061] For this purpose, a cooling model is preferably used that calculates the temperature distribution of the metal strip 2 in the rolling stands of the finishing train 10 and the rapid cooling system, preferably using the Fourier heat equation, and preferably across the entire strip thickness, thus enabling precise adjustment of the target values. Any deviation between measurement and calculation can be corrected at a temperature measuring point. This allows the temperature in the roll gap and in the cooling section of the rapid cooling device 20 to be optimally adjusted.

[0062] Furthermore, the cooling model can take into account the target coiling temperature, which must be precisely maintained depending on the application. The cooling model switches the necessary coolant quantities in the additional cooling device 30, which is located downstream of the rapid cooling system, to adjust the coiling temperature.

[0063] The coolant application via the spray bars 21, 2T of the rapid cooling device 20 is preferably variable across the width in order to compensate for incoming temperature profiles and to achieve uniform temperatures and thus properties across the width of the metal strip 2 on the exit side. The final rolling temperature, i.e., the temperature of the metal strip 2 upon entering the rapid cooling device 20, can be regulated by changing the speed in the finishing train 10. The coiler temperature can be regulated by changing the coolant quantity, particularly in the additional cooling device 30.

[0064] The immediate, strong cooling of the metal strip 2 after the last forming pass in the finishing train 10 described herein results in the creation of a very fine microstructure and thus an improvement in the mechanical properties of the metal strip 2.

[0065] Where applicable, all individual characteristics listed in the

[0066] embodiments are shown, combined and / or exchanged with each other without departing from the scope of the invention.

[0067] List of reference symbols

[0068] 1 Device for producing a metal strip

[0069] 2 metal bands

[0070] 10 Finishing line

[0071] 11 Last rolling stand

[0072] 20 Rapid cooling device

[0073] 21 spray booms

[0074] 21 ' End spray booms

[0075] 22 nozzle

[0076] 22' nozzle of an end spray boom

[0077] 23 Coolant supply

[0078] 24 Coolant supply line

[0079] 25 squeezing roller

[0080] 26 Air blow-off

[0081] 30 Additional cooling equipment

[0082] 31 spray booms

[0083] 40 reel device

[0084] 50 temperature gauges

[0085] 60 temperature gauges

[0086] F Conveying direction

[0087] Li Length of the cooling section of the rapid cooling device

[0088] L2 Distance between the roll gap of the last rolling stand and the further cooling device

Claims

Patent claims 1. Apparatus (1) for producing a hot-rolled metal strip (2), comprising: a finishing train (10) with at least one rolling stand (11) having work rolls forming a roll gap, for hot-rolling the metal strip (2); and a rapid cooling device (20) arranged immediately behind the roll gap of the last rolling stand (11) of the finishing train (10) and configured to rapidly cool the metal strip (2) by applying a coolant, preferably water-based, to the top and bottom of the metal strip (2) along a cooling section of the rapid cooling device (20); wherein the rapid cooling device (20) is configured to apply a coolant quantity of between 100 and 300 m to both the top and bottom of the metal strip (2). 3 / (m 2 *h) to be applied.

2. Device (1) according to claim 1, characterized in that the rapid cooling device (20) has, on the upper and lower sides, relative to the metal strip (2), spray bars (21, 21') each having a plurality of nozzles (22, 22') for spraying the coolant onto the metal strip (2), wherein the number of nozzles (22, 22') on the upper side is preferably 50 to 120 nozzles / m 2 and on the underside preferably 80 to 150 nozzles / m 2 wherein the upper nozzles (22, 22') are preferably arranged at most 800 mm above the metal strip (2) and the lower nozzles (22, 22') are preferably arranged at most 170 mm below the metal strip (2), wherein the diameter of the nozzles (22, 22') is preferably in the range from 3 to 8 mm.

3. Device (1) according to claim 2, characterized in that the rapid cooling device (20) has a coolant supply (23) and one or more coolant feed lines (24) which are in fluid communication with the spray bars (21) for supplying the nozzles (22, 22') with the coolant, wherein the coolant supply (23) is designed to set the pre-pressure of the coolant in the coolant feed lines (24) preferably to a pressure of 2 to 5 bar.

4. Device (1) according to claim 2 or 3, characterized in that the rapid cooling device (20) has one or more end-side spray bars (21 ') in each case in the front and / or rear region of the rapid cooling device (20), which are arranged such that their nozzles (22') apply the coolant to the metal strip (2) at an angle which is directed obliquely into the interior of the rapid cooling device (20).

5. Device (1) according to one of the preceding claims, characterized in that a squeeze roller (25) and / or an air blower (26) is installed and arranged at the inlet and / or outlet of the rapid cooling device (20) in order to prevent coolant from escaping from the cooling section of the rapid cooling device (20).

6. Device (1) according to one of the preceding claims, characterized in that the rapid cooling device (20) is arranged to set cooling rates for which the following applies: cooling rate * strip thickness > 500 K / s * mm.

7. Device (1) according to one of the preceding claims, characterized in that the length (Li) of the cooling section of the rapid cooling device (20) is preferably at least 4 m and / or a maximum of 10 m, preferably approximately 9 m.

8. Device (1) according to one of the preceding claims, characterized in that the rapid cooling device (20) is arranged to apply at least twice more coolant to the underside of the metal strip (2) than to the top side of the metal strip (2).

9. Device (1) according to one of the preceding claims, characterized in that the rapid cooling device (20) is designed to apply a total amount of coolant of at least 800 m 3 / h per meter of strip width, preferably at least 1500 m 3 / h, particularly preferably at least 2400 m 3 / h.

10. Device (1) according to one of the preceding claims, characterized in that the device (1) has a further cooling device (30) downstream of the rapid cooling device (20), which is designed to set the metal strip (2) to the desired final temperature, preferably a suitable coiling temperature, wherein the further cooling device (30) is preferably designed for laminar cooling.

11. A method for producing a hot-rolled metal strip (2), comprising: Hot rolling of a metal strip (2) in a finishing train (10) with at least one rolling stand (11) having work rolls forming a roll gap; and immediate cooling of the metal strip (2) following the hot rolling in the finishing train (10) by applying a coolant, preferably water-based, to the top and bottom of the metal strip (2) along a cooling section of the rapid cooling device (20), wherein the rapid cooling device (20) is arranged immediately behind the roll gap of the last rolling stand (11) of the finishing train (10); wherein the rapid cooling device (20) applies a quantity of coolant between 100 and 300 m to both the top and the bottom of the metal strip (2) 3 / (m 2 *h) applies.

12. The method according to claim 11, characterized in that the rapid cooling device (20) on the top and bottom, seen relative to the metal strip (2), has spray bars (21, 21') each with a plurality of nozzles (22, 22') for spraying the coolant onto the metal strip (2), a coolant supply (23) and one or more coolant feed lines (24), which are in fluid communication with the spray bars (21), for supplying the nozzles (22, 22') with the coolant, wherein the coolant supply (23) sets the pre-pressure of the coolant in the coolant feed lines (24) preferably to a pressure of 2 to 5 bar.

13. Method according to claim 12, characterized in that the rapid cooling device (20) has one or more end-side spray bars (21') in each case in the front and / or rear region of the rapid cooling device (20), the nozzles (22') of which apply the coolant to the metal strip (2) at an angle which is directed obliquely into the interior of the rapid cooling device (20).

14. Method according to one of claims 11 to 13, characterized in that a cooling rate is set in the rapid cooling device (20) for which the following applies: cooling rate * strip thickness > 500 K / s * mm.

15. Method according to one of claims 11 to 14, characterized in that in the rapid cooling device (20) the underside of the metal strip (2) is exposed to at least twice as much coolant as the top side of the metal strip (2).

16. Method according to one of claims 11 to 15, characterized in that in the rapid cooling device (20) a total amount of coolant is applied to the top and bottom of the metal strip (2) of at least 800 m 3 / h per meter of strip width, preferably at least 1500 m 3 / h, particularly preferably at least 2400 m 3 / h.

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