US-12623278-B2 - Method for producing a microalloyed steel, a microalloyed steel produced using the method, and a combined casting/rolling installation

US12623278B2US 12623278 B2US12623278 B2US 12623278B2US-12623278-B2

Abstract

A process that produces a microalloyed steel in an integrated casting-rolling plant having a continuous casting machine with a mold, a single- or multi-stand prerolling train, a finish-rolling train having a first stand group with at least one first finish-rolling stand and a second stand group having at least one stand cooler. A metallic melt is cast in the mold to obtain a partly solidified thin-slab strand, which is supported, deflected and cooled. The solidified thin-slab strand is rolled by the prerolling train to obtain a prerolled strip that is finish-rolled in the first stand group to obtain the finish-rolled strip, which is fed to the second stand group and force-cooled in the second stand group, the finish-rolled strip having a thickness that results in a cooling rate of the core of the finish-rolled strip in the second stand group greater than 20° C./s and less than 200° C./s.

Inventors

Kerstin BAUMGARTNER
Simon GROSSEIBER
Thomas Lengauer
Gero SCHWARZ

Assignees

Primetals Technologies Austria GmbH

Dates

Publication Date: 20260512
Application Date: 20220525
Priority Date: 20210609

Claims (15)

1 . A process for producing a microalloyed steel in an integrated casting-rolling plant having a continuous casting machine having a mold, a single- or multi-stand prerolling train, a finish-rolling train having a first stand group with at least one first finish-rolling stand and a second stand group having at least one stand cooler, the process comprising: casting a metallic melt in the mold to give a partly solidified thin-slab strand, supporting, deflecting, and cooling the partly solidified thin-slab strand to give a fully solidified thin-slab strand, rolling the fully solidified thin-slab strand with the prerolling train to give a prerolled strip, finish-rolling the prerolled strip with the first stand group of the finish-rolling train to give a finish-rolled strip, feeding, immediately after the finish rolling, the finish-rolled strip to the second stand group, and force-cooling the finish-rolled strip in the second stand group with retention of a thickness of the finish-rolled strip in such a way that a cooling rate of a core of the finish-rolled strip in the second stand group is greater than 20° C./s and less than 200° C./s, and transporting the finish-rolled strip through a cooling zone downstream of the finish-rolling train based on a conveying direction of the finish-rolled strip to a winding device downstream of the cooling zone while further cooling the finish-rolled strip, wherein the finish-rolled strip is transported with a first exit temperature (TA 1 ) at its core into the second stand group of the finish-rolling train, wherein, upon exiting of the finish-rolled strip from the second stand group, the core of the finish-rolled strip has a second exit temperature (TA 2 ) lower than the first exit temperature (TA 1 ).
2 . The process as claimed in claim 1 , wherein the second stand group has a second finish-rolling stand, further comprising converting the second finish-rolling stand, in a preparation step prior to casting of the metallic melt, to the stand cooler by removing at least one working roll of the second finish-rolling stand and inserting at least one cooling beam into the second finish-rolling stand.
3 . The process as claimed in claim 1 , further comprising ascertaining with a temperature measurement device a third surface temperature with which the finish-rolled strip leaves the second stand group, wherein the force-cooling in the second stand group is controlled by open-loop/closed-loop control depending on the third surface temperature and a third target temperature (TS 3 ) in such a way that the third surface temperature corresponds essentially to the third target temperature (TS 3 ), wherein the third target temperature (TS 3 ) is less than a ferrite-perlite transformation temperature (Ar 1 ).
4 . The process as claimed in claim 1 , wherein the cooling rate of the core of the finish-rolled strip is 20° C./s to 80° C./s, wherein the core of the finish-rolled strip is cooled continuously.
5 . The process as claimed in claim 1 , wherein the first exit temperature (TA 1 ) is in a range 830° C. to 950° C., wherein the second exit temperature (TA 2 ) is less than 700° C.
6 . The process as claimed in claim 1 , wherein, within a time interval of 1 second to 15 seconds after the finish-rolling of the finish-rolled strip in the first stand group, the finish-rolled strip enters the second stand group.
7 . The process as claimed in claim 1 , wherein forced cooling of the finish-rolled strip in the cooling zone is deactivated.
8 . The process as claimed in claim 1 , wherein a thickness of the prerolled strip on entry into the first stand group is 40 mm to 62 mm, wherein the first stand group reduces the thickness of the prerolled strip to that of the finish-rolled strip of 10 mm to 25 mm.
9 . The process as claimed in claim 1 , wherein the metallic melt is an X60 or an X70 steel melt and has a chemical composition in percent by weight of C 0.025-0.05%; Si 0.1-0.3%; Mn 0.07-1.5%, Cr<0.15%; Mo<0.2%; Nb 0.02-0.08%; Ti<0.05%; V<0.08%; N<0.008%; balance: Fe and unavoidable impurities, or wherein the metallic melt is an X80 to X120 steel melt and has a chemical composition in percent by weight of C 0.025-0.09%; Si 0.1-0.3%; Mn 0.07-2.0%, Cr<0.5%; Mo<0.5%; Nb 0.02-0.08%; Ti<0.05%; V<0.08%; Ni<0.5%; Cu<0.4%; N<0.01%; balance: Fe and unavoidable impurities.
10 . The process as claimed in claim 1 , wherein a third surface temperature with which the finish-rolled strip leaves the second stand group is ascertained, wherein the forced cooling in the second stand group is controlled by open-loop/closed-loop control depending on the third surface temperature and a third target temperature (TS 3 ) in such a way that the third surface temperature corresponds to the third target temperature (TS 3 ), wherein the third target temperature (TS 3 ) is less than a bainite start temperature.
11 . The process as claimed in claim 1 , wherein a third surface temperature with which the finish-rolled strip leaves the second stand group is ascertained, wherein the forced cooling in the second stand group is controlled by open-loop/closed-loop control depending on the third surface temperature and a third target temperature (TS 3 ) in such a way that the third surface temperature corresponds to the third target temperature (TS 3 ), wherein the third target temperature (TS 3 ) is less than a martensite start temperature (M s ).
12 . The process as claimed in claim 1 , wherein the first exit temperature (TA 1 ) is in a range 830° C. to 950° C., wherein the second exit temperature (TA 2 ) is in a range 350° C. to 700° C.
13 . The process as claimed in claim 1 , wherein the first exit temperature (TA 1 ) is in a range of 830° C. to 950° C., wherein the second exit temperature (TA 2 ) is in a range 400° C. to 460° C.
14 . The process as claimed in claim 3 , further comprising ascertaining with another temperature measurement device a second surface temperature with which the finish-rolled strip leaves the first stand group, wherein the second surface temperature is also taken into account in the control of the forced cooling of the finish-rolled strip in the second stand group.
15 . The process as claimed in claim 4 , wherein the core of the finish-rolled strip is cooled, from the first exit temperature (TA 1 ) to the second exit temperature (TA 2 ) within a time interval of 2 seconds to 40 seconds.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS The present application is a national stage application of PCT application PCT/EP2022/064188, filed May 25, 2022, which claims priority to the European patent application, EP21178473, Jun. 9, 2021, the contents of which are incorporated by this reference. FIELD OF INVENTION The invention relates to a process for producing a microalloyed steel according to claim 1, to a microalloyed steel according to claim 12, and to an integrated casting-rolling plant according to claim 14. BACKGROUND WO 2019/020492 A1 discloses a rolling stand having a stand cooler for cooling of a steel strip. US 2016/151814 A1 discloses a plant and a process for hot rolling of a steel strip. EP 2 398 929 A1 discloses a high-strength and thin cast strip product and a production process therefor. “Microstructural Evolution and Strengthening Mechanism of X65 Pipeline Steel Processed by Ultra-fast Cooling”, published in the Journal of Northeastern University (Natural Science) vol. 40, no. 3, 1 Mar. 2019, pages 334-338, XP009531477, ISSN 1005-3026, discloses a process for producing X65 pipeline steel. Moreover, WO 2020/126473 A1 discloses cooling of a metal strip in a rolling stand. AT 512 399 B1 discloses a process for producing a microalloyed piping steel in an integrated casting-rolling plant. SUMMARY It is an object of the invention to provide an improved process for producing a microalloyed steel in an integrated casting-rolling plant, an improved microalloyed steel and an improved integrated casting-rolling plant. This object is achieved by a process according to claim 1, by a microalloyed steel, especially a microalloyed piping steel, according to claim 12, and by an integrated casting-rolling plant according to claim 14. Advantageous embodiments are specified in the dependent claims. It has been recognized that an improved process for producing a microalloyed steel in an integrated casting-rolling plant can be provided in that the integrated casting-rolling plant has a continuous casting machine with a mold, a single- or multi-stand prerolling train, a finish-rolling train having a first stand group with at least one first finish-rolling stand and a second stand group having at least one stand cooler. A metallic melt is cast in the mold to give a partly solidified thin-slab strand. In this application, strand-cast strands with a thickness of ≤150 mm are referred to as thin-slab strands. The partly solidified thin-slab strand is supported, deflected and cooled. The thin-slab strand is rolled in the prerolling train to give a prerolled strip. The first stand group of the finish-rolling train finish-rolls the prerolled strip to give the finish-rolled strip. Immediately after the finish rolling, the finish-rolled strip is fed to the second stand group and the finish-rolled strip is force-cooled in the second stand group with retention of a thickness of the finish-rolled strip in such a way that a cooling rate of a core of the finish-rolled strip in the second stand group is greater than 20° C./s and less than 200° C./s. This configuration has the advantage that—preferably in continuous operation—the microalloyed steel can be produced in a simple manner. In particular, it is thus also possible, for example, with a metallic melt containing 10% less microalloy elements (for example titanium, niobium and/or vanadium), corresponding, for example, to an X60 to X120 steel according to standard API 5L/IS03183:2007, to produce a microalloyed steel that meets the mechanical demands for the steel qualities according to the standard cited. By the method, it is thus possible to produce the microalloyed steel in a particularly simple and inexpensive manner. In continuous operation of the integrated casting-rolling plant, a continuously produced thin-slab strand is prerolled and finish-rolled in uncut form, and the microalloyed steel is cut to bundle length for the first time after passing through the cooling zone. In a further embodiment, the second stand group has a second finish-rolling stand, wherein the second finish-rolling stand, in a preparation step prior to casting of the metallic melt, is converted to the stand cooler by removing at least one working roll of the second finish-rolling stand and inserting at least one cooling beam into the second finish-rolling stand. In this way, it is possible to convert the integrated casting-rolling plant in a particularly simple manner. In a further embodiment, a third surface temperature with which the finish-rolled strip leaves the second stand group is ascertained. The forced cooling in the second stand group is controlled by open-loop/closed-loop control depending on the third surface temperature and a third target temperature in such a way that the third surface temperature corresponds essentially to the third target temperature. This third target temperature is less than a ferrite-perlite transformation temperature, preferably less than a bainite start tempera