Production lines and methods for hot rolling steel strip

Patent metadata

Field	Value
Publication number	US-10335840-B2
Application number	US-201414902812-A
Country	US
Kind code	B2
Filing date	Jul 1, 2014
Priority date	Jul 3, 2013
Publication date	Jul 2, 2019
Grant date	Jul 2, 2019

Abstract

The present disclosure relates to production lines and methods for hot rolling steel strips. Example production lines may include a hot rolling line that comprises a plurality of rolling stands through which a steel strip passes in a conveying direction. The production line may also include a cooling section for intensively cooling the steel strip as the steel strip exits a final rolling stand of the rolling line. The steel strips may be deformed so as to have a thickness of more than 15 mm and to comply with the most stringent requirements with respect to, for example, toughness. Further, at least a portion of the cooling section may overlap with a portion of the hot rolling line.

First claim

What is claimed is:

1. A production line for hot rolling a steel strip, the production line comprising:
a hot rolling line having a plurality of rolling stands, the plurality of rolling stands comprising,
a plurality of successive active rolling stands disposed at an upstream end of the hot rolling line, and
at least one inactive rolling stand disposed downstream of the plurality of active rolling stands in a conveying direction of the steel strip to be hot rolled,

the hot rolling line is configured to hot roll the steel strip by passing the steel strip successively through the plurality of rolling stands in the conveying direction; and
a cooling section configured to cool the hot rolled steel strip after exiting a last of the active rolling stands, the cooling section having an upstream end positioned to start after the last of the active rolling stands and before the at least one inactive rolling stand such that at least a portion of the cooling section is shifted to be located upstream of the at least one inactive rolling stand of the hot rolling line, the cooling section comprising at least,
a first cooling unit disposed at the upstream end of the cooling section and positioned between the last of the active rolling stands and the at least one inactive rolling stand, and
a second cooling unit disposed downstream of the at least one inactive rolling stand,
wherein the first cooling unit subjects the steel strip to cooling fluid along a length of the steel strip measured with respect to the conveying direction that is at most 25% of a distance between the last of the active rolling stands and the at least one inactive rolling stand.

2. The production line of claim 1 , wherein
the hot rolling line further comprises a plurality of successive inactive rolling stands disposed downstream of the plurality of active rolling stands in the conveying direction, and
the cooling section further comprises a plurality of cooling units including the first and second cooling units, wherein at least one of the plurality of cooling units is disposed between two successive inactive rolling stands of the plurality of inactive rolling stands.

3. The production line of claim 2 wherein at least one cooling unit is disposed in a portion of the cooling section that is disposed downstream of a last of the plurality of inactive rolling stands.

4. The production line of claim 2 wherein each of the plurality of cooling units in the cooling section are independently controllable.

5. The production line of claim 2 wherein at least one of the plurality of cooling units disposed in a portion of the cooling section that is upstream of at least one inactive rolling stand of the hot rolling line is configured as a compact cooling unit.

6. The production line of claim 5 , further comprising a spraying device positioned downstream of the first cooling unit wherein the spraying device is configured to direct a liquid jet onto the steel strip to drive the cooling fluid off the steel strip before the steel strip enters a first inactive roll stand in the conveying direction of the plurality of roll stands and/or a spraying device positioned downstream of at least one of the plurality of cooling units disposed between one of the plurality of inactive rolling stands of the plurality of inactive rolling stands and the next successive inactive rolling stand of the plurality of inactive rolling stands in the conveying direction, wherein the spraying device is configured to direct a liquid jet onto the steel strip to drive the cooling fluid off the steel strip before the steel strip enters the successive inactive rolling stand.

7. The production line of claim 1 wherein the cooling section has a total cooling fluid output of at least 1000 m 3 /h.

8. A method for hot rolling a steel strip, the method comprising:
hot rolling the steel strip in a hot rolling line by passing the steel strip through a plurality of rolling stands in a conveying direction, the plurality of rolling stands including a plurality of active rolling stands followed by at least one inactive rolling stand, the hot rolling step including,
first passing the steel strip through the plurality of active rolling stands such that the active rolling stands contact and deform the steel strip passing there through, and
next passing the hot roll deformed steel strip through the at least one inactive rolling stand, wherein a rolling gap of working rollers of the inactive rolling stand are opened to such an extent that the working rollers do not contact the deformed steel strip, and thereby do not further deform the steel strip;

cooling the steel strip in a cooling section, wherein the cooling section has an upstream end that starts after a last of the active rolling stands and before the at least one inactive rolling stand such that at least a portion of the cooling section is shifted to be located upstream of the at least one inactive rolling stand of the hot rolling line, the cooling section comprises a first cooling unit disposed at the upstream end of the cooling section and positioned between the last of the active rolling stands and the at least one inactive rolling stand and a second cooling unit disposed downstream of the at least one inactive rolling stand, and the first cooling unit subjects the steel strip to cooling fluid along a length of the steel strip measured with respect to the conveying direction that is at most 25% of a distance between the last of the active rolling stands and the at least one inactive rolling stand,
wherein the steel strip is cooled at a rate of at least 80 K/s after the steel strip exits a last of the plurality of active rolling stands that deforms the steel strip.

9. The method of claim 8 wherein hot rolling the steel strip comprises deforming the steel strip to have a thickness of at least 15 mm at a point where the steel strip exits the hot rolling line.

10. The method of claim 8 wherein the steel strip passes through the at least one inactive rolling stand at a speed of less than 3 m/s.

11. The method of claim 8 further comprising heating the steel strip to a temperature of between 800 and 1050 degrees Celsius prior to hot rolling.

12. The method of claim 8 wherein the steel strip is at a temperature of between 740 and 900 degrees Celsius when the steel strip leaves a last of the active rolling stands in the conveying direction and enters the cooling section.

13. The method of claim 8 wherein cooling of the steel strip is stopped at a cooling-stop temperature of between 500 and 700 degrees Celsius.

14. The method of claim 13 further comprising maintaining the steel strip at the cooling-stop temperature for 2 to 12 seconds after the steel strip reaches the cooling-stop temperature.

15. The method of claim 8 further comprising coiling the steel strip at a coiling temperature of between 450 and 650 degrees Celsius.

16. The method of claim 8 wherein a thickness of the steel strip upon entering the hot rolling line is between 50 and 100 mm, and wherein the thickness of the steel strip is between 15 and 25.5 mm upon exiting the hot rolling line.

17. The method of claim 8 wherein the steel strip comprises iron, impurities, and in percentage by weight less than or equal to 0.18% C, less than or equal to 1.5% Si, less than or equal to 2.5% Mn, 0.005-0.1% P, less than or equal to 0.03% S, less than or equal to 0.02% N, less than or equal to 0.5% Cr, less than or equal to 0.5% Cu, less than or equal to 0.5% Ni, less than or equal to 0.5% Mo, less than or equal to 2% Al, and up to a total of 0.3% of one or more of e

Assignees

• Thyssenkrupp Steel Europe Ag

Inventors

• Fischer Heribert
• Schmitt Caspar
• Zaum Andreas

Classifications

• C21D9/573

  with cooling · CPC title

• B21B45/0218

  for strips, sheets, or plates (B21B45/023, B21B45/0233 take precedence) · CPC title

• C21D8/0231

  Warm rolling · CPC title

• B21B1/22 Primary

  for rolling {plates, strips,} bands or sheets of indefinite length (B21B1/42 takes precedence) · CPC title

• B21B2001/225

  by hot-rolling · CPC title