Method for producing a metal strip

Abstract

A method for producing a metal strip, in which the strip is rolled in a multi-stand rolling mill, is removed behind the final rolling stand of the rolling mill in the direction of conveyance, and is cooled in a cooling device. The strip or metal sheet is subjected to additional rapid cooling immediately after passing the working rollers of the final rolling stand, wherein the strip or the metal sheet is cooled at least partially within the extent of the final rolling stand in the direction of conveyance, wherein rapid cooling is performed by applying a coolant to the strip or metal sheet from above and from below, wherein the volume flow of coolant that is applied to the strip or metal sheet from below measures at least 120% of the volume flow of coolant that is applied to the strip or metal sheet from above.

Claims

1. A method for producing a metal strip or plate, in which the strip or plate is rolled in a multi-stand rolling mill, is output after the final rolling stand of the rolling mill in the direction of conveyance and is cooled in a cooling device, wherein, immediately after passing the working rolls of the final rolling stand, the strip or plate is subjected to an additional rapid cooling, the cooling of the strip or plate at least partially taking place still within the extent of the final rolling stand in the direction of conveyance, the rapid cooling taking place by a cooling medium being applied to the strip or plate from above and from below, wherein during rapid cooling the volumetric flow of cooling medium that is applied to the strip or plate from below is at least 200% of the volumetric flow of cooling medium that is applied to the strip or plate from above, wherein, with the rapid cooling of the strip or plate, a cooling medium is applied in such an amount and/or at such a pressure that the cooling of the strip or plate at its surface takes place with a gradient of at least 500 K/s and wherein the rapid cooling extends from within the final rolling stand of the rolling mill in the direction of conveyance over a distance of between 2 m and 15 m, and wherein the cooling device begins at a distance of at least 10 m after the final rolling stand of the rolling mill in the direction of conveyance.

2. The method as claimed in claim 1, wherein the volumetric flow of cooling medium that is applied to the strip or plate from below is at most 400% of the volumetric flow of cooling medium that is applied to the strip or plate from above.

3. The method as claimed in claim 1, wherein, with the rapid cooling of the strip or plate, a cooling medium is applied in such an amount and/or at such a pressure that the cooling of the strip or plate at its surface takes place with a gradient of at least 750 K/s.

4. The method as claimed in claim 3, wherein, with the rapid cooling of the strip or plate, a cooling medium is applied in such an amount and/or at such a pressure that the cooling of the strip or plate at its surface takes place with a gradient of at least 1000 K/s.

5. The method as claimed in claim 1, wherein the strip or plate is produced by a thin slab first being cast in a continuous casting installation, this then being heated to a defined temperature in a furnace, and immediately after that rolled down to the final strip thickness in the rolling mill acting as the finishing train.

6. The method as claimed in claim 5, wherein the furnace is a roller hearth furnace.

7. The method as claimed in claim 1, wherein a steel strip or a steel plate is produced as the strip or plate.

8. The method as claimed in claim 1, wherein the rapid cooling extends from within the final rolling stand of the rolling mill in the direction of conveyance over a distance of between 6 m and 10 m.

9. The method as claimed in claim 1, wherein the cooling device begins at a distance of at least 13 m after the final rolling stand of the rolling mill in the direction of conveyance.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) An exemplary embodiment of the invention is represented in the drawing. The single FIGURE schematically shows the final stand of a finishing train for producing a steel strip and a following laminar cooling together with a coiling installation.

DETAILED DESCRIPTION OF THE INVENTION

(2) In the FIGURE, the rolling stand 2 of a finishing train can be seen. The strip 1 is rolled in the finishing train and leaves the final rolling stand 2 in the direction of conveyance F. Directly after the roll gap or already in the roll gap of the final rolling stand 2, the strip 1 is cooled, for which purpose rapid cooling 4 is used, corresponding in structural terms to the classic type of construction. A cooling medium (water) is sprayed onto the upper side and underside of the strip 1.

(3) After the rapid cooling 4 there follows a classic cooling device 3 in the form of a laminar cooling. In the exemplary embodiment, the cooling device 3 is divided into 10 portions.

(4) It is also worth mentioning that the length L.sub.1 of the rapid cooling 4 in the exemplary embodiment runs to about 9 m from the middle of the rolling stand 2; as described, the rapid cooling begins immediately after or in the roll gap of the final rolling stand 2.

(5) Meanwhile, in the exemplary embodiment the distance L.sub.2 of the cooling device 3, i.e. its beginning, lies about 14 m after the middle of the rolling stand 2.

(6) After the cooling device 3 there is a coiling device 5 for winding up the now finished strip.

(7) Temperature measuring elements 6 and 7 (pyrometers) determine the respective temperature at the corresponding location, in order to be able to monitor the progress of the process.

(8) It is achieved that the strength and the extension under strain of the strip (or of the plate) are increased at the same time, which is due to the small grain size that is achieved when the proposed method is used. After the rolling of the strip in the hot-strip train, an increase in the grain size takes place immediately after the recrystallization. This can be prevented if the temperature of the strip is reduced as quickly as possible after the rolling to a range in which an increase in the grain size no longer takes place. The strip must therefore be cooled from the final rolling temperature, which lies at about 800° C. to 920° C., on average at 860° C., to at least 700° C.

(9) With preference, the proposed method is used in combination with a CSP plant with X strands, oscillation and use of the tunnel furnace, or in a conventional hot-rolling mill.

(10) Special materials, for example microalloyed grades, may be used.

(11) A combination with a plate-rolling mill may also be provided.

LIST OF DESIGNATIONS

(12) 1 Strip 2 Rolling stand 3 Cooling device 4 Rapid cooling 5 Coiling device 6 Temperature measuring element 7 Temperature measuring element F Direction of conveyance L.sub.1 Length of the rapid cooling L.sub.2 Distance of the cooling device