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EP4438746A1 - Procédé de fabrication directe d'une bande d'acier trip dans une installation composite de coulée-laminage et bande d'acier trip ainsi fabriquée - Google Patents

Procédé de fabrication directe d'une bande d'acier trip dans une installation composite de coulée-laminage et bande d'acier trip ainsi fabriquée Download PDF

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Publication number
EP4438746A1
EP4438746A1 EP23164462.6A EP23164462A EP4438746A1 EP 4438746 A1 EP4438746 A1 EP 4438746A1 EP 23164462 A EP23164462 A EP 23164462A EP 4438746 A1 EP4438746 A1 EP 4438746A1
Authority
EP
European Patent Office
Prior art keywords
cooling
strip
finished strip
finished
inclusive
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP23164462.6A
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German (de)
English (en)
Inventor
Kerstin Baumgartner
Simon Grosseiber
Axel RIMNAC
Gero Schwarz
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Primetals Technologies Austria GmbH
Original Assignee
Primetals Technologies Austria GmbH
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Primetals Technologies Austria GmbH filed Critical Primetals Technologies Austria GmbH
Priority to EP23164462.6A priority Critical patent/EP4438746A1/fr
Priority to US18/411,282 priority patent/US20240327944A1/en
Priority to CN202480021640.2A priority patent/CN120858185A/zh
Priority to PCT/EP2024/057783 priority patent/WO2024200274A1/fr
Publication of EP4438746A1 publication Critical patent/EP4438746A1/fr
Pending legal-status Critical Current

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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
    • B21B1/22—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length
    • B21B1/24—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length in a continuous or semi-continuous process
    • B21B1/26—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length in a continuous or semi-continuous process by hot-rolling, e.g. Steckel hot mill
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/001—Continuous casting of metals, i.e. casting in indefinite lengths of specific alloys
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/14—Plants for continuous casting
    • B22D11/141—Plants for continuous casting for vertical casting
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/02—Hardening articles or materials formed by forging or rolling, with no further heating beyond that required for the formation
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/021—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a particular fabrication or treatment of ingot or slab
    • C21D8/0215—Rapid solidification; Thin strip casting
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/001—Austenite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/002—Bainite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite

Definitions

  • the invention relates to a method for producing a TRIP steel strip according to patent claim 1 and a TRIP steel strip according to patent claim 13.
  • an improved method for directly producing a TRIP steel strip in continuous operation can be provided in a casting-rolling composite plant which has a finishing rolling mill and a cooling section.
  • a hot preliminary strip is fed to the finishing rolling mill, which the finishing rolling mill finish-rolls into a finished strip.
  • the finished strip is fed to a first cooling group of the cooling section and in the first cooling group a core of the finished strip is forcibly cooled to a second exit temperature such that the second exit temperature is in a range from 620°C to 700°C.
  • the core of the finished strip leaves the first cooling group, it has a predominantly, preferably at least 90% phase content, in particular at least 95% phase content, in particular a completely austenitic structure.
  • the cooled finished strip is transported to a third cooling group of the cooling section, whereby a second cooling rate of the core of the finished strip is established during the transport of the finished strip between the first cooling group and the third cooling group, whereby the second cooling rate of the core of the finished strip is -25 K/s inclusive, in particular 0 K/s inclusive, up to and including 20 K/s inclusive.
  • a first part of the austenitic structure in the finished strip is converted into a ferritic structure.
  • the core of the finished strip is heated to a third exit temperature which is less than or equal to the bainite start temperature.
  • the cooling can take place in the third cooling group in such a way that the first part of the austenite is ideally converted into a cementite-free bainite.
  • the advantage is that the TRIP strip is finished at the end of the process, regardless of its final thickness.
  • an additional cold rolling step and/or an annealing step after the cooling line can be avoided.
  • the direct production of the TRIP strip makes the process described above particularly energy-efficient.
  • the process can be used to produce a TRIP780/HCT780T strip particularly cost-effectively. It is also ensured that the finished strip has already reached its final thickness during the hot rolling and not during the cold rolling step.
  • the second cooling rate can also be negative due to the phase transformations that occur during transport and the resulting heat of transformation.
  • the low second cooling rate during transport which is achieved, for example, by dispensing with forced cooling, results in a high degree of homogeneity of the structure in the TRIP strip. Furthermore, a defined and reproducible phase proportion of metastable austenite and bainite is ensured by the low second cooling rate with high process reliability.
  • the direct production of the finished rolled strip in continuous operation i.e. when the finished rolled strip is mechanically connected to the rough rolled strip and to the thin slab strand, has the further advantage that extremely high reductions can be achieved per rough rolled and/or finishing roll stand. This means that even high-strength grades can be hot rolled directly to low strip thicknesses, such as those required for lightweight automotive construction.
  • the entire time during which the second cooling rate prevails is also referred to as the holding time, during which only natural cooling can occur due to a convention through the deactivated second cooling group or the finished strip can heat up due to phase transformations during the holding time.
  • the second low cooling rate gives the structure enough time during transport between the first cooling group and the third cooling group to transform the desired phase proportion of at least 50% of austenite into ferrite at the set temperature.
  • the process described above which is carried out exclusively in (quasi) continuous operation, has the advantage that acceleration of the finished strip can be avoided. This ensures that the process parameters required for the production of the TRIP strip, especially in the area of the cooling section, can be reliably maintained over a long period of time. This ensures a high level of homogeneity across the entire TRIP strip produced.
  • the process described above ensures that good castability and thus the casting speeds and mass flows required for the continuous process can be maintained. Furthermore, thanks to the process described above, the TRIP strip has a low tendency to surface defects, for example caused by selective (high-temperature) oxidation of the austenite grain boundaries during continuous casting, as well as a low tendency to internal oxidation and internal cracking.
  • the second outlet temperature of 620°C to 700°C inclusive ensures that during transport between the first cooling group and the third cooling group, a rapid formation of ferrite is ensured and that a globular ferrite is also formed. This has a positive effect on the mechanical properties of a microstructure of the TRIP steel. Furthermore, the spatial distance between the first cooling group and the third cooling group can be shortened by the rapid formation of the globular ferrite.
  • the cooled finished strip is fed to a second cooling group of the cooling section after leaving the first cooling group, wherein forced cooling of the finished strip in the second cooling group is deactivated and the finished strip in the second cooling group is transported to a third cooling group of the cooling section.
  • the finished strip is coiled and cooled in the coil from the third exit temperature to an ambient temperature.
  • a remaining second part of the austenite of the finished strip is enriched with carbon (which is essentially insoluble in the cementite-free bainite), so that a metastable residual austenite portion is formed.
  • the metastable residual austenite is converted into martensite during cold deformation, particularly during rapid cold deformation, for example in the event of a motor vehicle crash.
  • the metastable Residual austenite can also be converted into martensite during cold forming of the finished rolled strip, so that the component produced by forming technology, for example a bodywork component, is particularly stiff and tough.
  • the finished strip is forced cooled in the first cooling group in such a way that a first cooling rate of the core of the finished strip is established.
  • the finished strip is forced cooled in such a way that a third cooling rate of the core of the finished strip is established.
  • the second cooling rate is lower than the first cooling rate and/or the third cooling rate.
  • the first cooling rate and/or the third cooling rate of the core of the finished strip is preferably 20 K/s to 400 K/s, in particular 50 K/s to 200 K/s. This design has the advantage that the first high cooling rate leads to rapid cooling into the (partially) ferritic range. This in turn promotes the rapid formation of homogeneous ferrite grains from the austenitic structure.
  • the third cooling rate is necessary to avoid a conversion of the remaining austenite into ferrite. Instead, thanks to the high second cooling rate, the remaining second part of the austenite is largely converted into bainite.
  • the residual austenite remains partially between the bainite plates. Cementite precipitation is hindered by the alloy components silicon and/or aluminum, which means that the carbon cannot precipitate as iron carbide and is thus enriched in the residual austenite remaining between the bainite plates.
  • the core of the finished strip has a first exit temperature above the ferrite precipitation temperature (Ar3 temperature), in particular from 800 °C to 950 °C, in particular from 830 °C to 860 °C, when exiting the finishing rolling train.
  • Ar3 temperature the ferrite precipitation temperature
  • the core of the finish-rolled strip leaves the second cooling group with a third exit temperature of 580 °C to 680 °C inclusive, in particular of 620 °C to 660 °C inclusive, and is transported to the third cooling group of the cooling section. Furthermore, when the finished strip exits the third cooling group, the core of the finished strip has a fourth exit temperature, whereby when the finished strip 165 exits the third cooling group 168, the core of the finished strip 165 has a fourth exit temperature TA4 of 180°C up to and including 450°C, in particular 330°C up to and including 360°C, in particular 420°C up to and including 330°C, in particular 390°C up to and including 390°C.
  • the core of the finished strip is cooled from the fourth exit temperature to an ambient temperature within a fourth time interval of 24 hours to 72 hours.
  • the ambient temperature is usually -20 °C to +50 °C.
  • the slow (natural and convective) cooling of the finished strip ensures that there is enough time for the carbon, which is practically insoluble in ferrite, to diffuse into the residual austenite, thus forming a residual austenite that is metastable at ambient temperature.
  • a thickness of the preliminary strip when entering the finishing rolling mill is 4 mm to 25 mm, in particular 6 mm to 18 mm.
  • the finishing rolling mill reduces the thickness of the preliminary strip to the finished strip to 0.6 mm to 6 mm inclusive, in particular to 0.8 mm to 2 mm inclusive.
  • the finished strip has a chemical composition in percent by weight of C inclusive of 0.15% up to and including 0.25%, in particular inclusive of 0.19% up to and including 0.21%, Mn 1.0% up to and including 2.0%, in particular 1.4% up to and including 1.6%, Si 1.0% up to and including 1.5%, in particular 1.1% up to and including 1.3%, Al inclusive of 0.3% up to and including 0.7%, in particular inclusive of 0.45% up to and including 0.55%, balance Fe and unavoidable impurities.
  • the combined casting and rolling plant has a continuous casting machine with a mold and a single or multi-stand roughing mill, whereby a metallic melt is cast in the mold to form a partially solidified thin slab strand, whereby the partially solidified thin slab strand is supported and diverted, whereby the partially solidified thin slab strand from the continuous casting machine is fed directly to the roughing mill, whereby the roughing mill rolls the thin slab strand to form the preliminary strip, whereby the preliminary strip is fed to the finishing mill without interruption. Due to the uninterrupted feeding of the thin slab strand to the roughing mill and the uninterrupted feeding of the preliminary strip to the finishing mill, the TRIP strip is produced in continuous operation with particularly little energy consumption. Due to the uninterrupted production, the finished strip is mechanically connected to the preliminary strip and mechanically connected to the thin slab strand. The TRIP strip is produced directly without the use of intermediate storage or pre-strip separation, for example by shearing.
  • a high rolling temperature in the finishing rolling mill and rolling to a particularly thin final thickness is ensured by arranging an intermediate heating system between the roughing mill and the finishing mill, the intermediate heating system heating a core of the preliminary strip by at least 100°C up to and including 300°C, in particular to 1100°C up to and including 1180°C, the heated preliminary strip being fed to the finishing rolling mill.
  • the TRIP steel strip is manufactured using the process described above.
  • the TRIP steel strip has a chemical composition in percent by weight of C inclusive of 0.15% up to and including 0.25%, in particular inclusive of 0.19% up to and including 0.21%, Mn 1.0% up to and including 2.0%, in particular 1.4% up to and including 1.6%, Si 1.0% up to and including 1.5%, in particular 1.1% up to and including 1.3%, Al inclusive of 0.3% up to and including 0.7%, in particular inclusive of 0.45% up to and including 0.55%, the remainder being Fe and unavoidable impurities.
  • the finished strip has the following microstructure at room temperature based on percent by volume: from and including 40% ferrite up to and including 60%, in particular from and including 45% up to and including 55% ferrite, from and including 8% up to and including 15% metastable residual austenite, the remainder being bainite, preferably free of cementite.
  • the TRIP steel strip has a thickness of 0.6 mm to 6 mm inclusive, in particular 0.8 mm to 2 mm inclusive.
  • FIG 1 shows a schematic representation of a casting-rolling composite plant 10 for producing a TRIP steel strip 245.
  • the combined casting and rolling plant 10 comprises, for example, a continuous casting machine 15, a roughing train 20, preferably a first to third separating device 25, 30, 35, an intermediate heating system 45, preferably a descaler 50, a finishing train 55, a cooling section 65, at least one, preferably second, coiling device 70 and a control device 75.
  • the continuous casting machine 15 is designed, for example, as a curved continuous casting machine. Another design of the continuous casting machine 15 would also be conceivable.
  • the continuous casting machine 15 has a ladle 95, a distributor 100 and a mold 105.
  • the distributor 100 is filled with a metallic melt 110 by means of the ladle 95.
  • the metallic melt 110 can be produced, for example, by means of a converter, for example in a Linz-Donawitz process.
  • the metallic melt 110 can, for example, comprise steel.
  • the metallic melt 110 flows from the distributor 100 into the mold 105. In the mold 105, the metallic melt 110 is cast to form a thin slab strand 115.
  • the partially solidified thin slab strand 115 is pulled out of the mold 105 and, due to the design of the continuous casting machine 15 as an arc-shaped continuous casting machine, is deflected in an arc-shaped manner into a horizontal position, supported and solidified in the process.
  • the thin slab strand 115 is conveyed away from the mold 105 in the conveying direction.
  • the roughing mill 20 is arranged downstream of the continuous casting machine 15. In this embodiment, the roughing mill 20 directly follows the continuous casting machine 15.
  • the roughing mill train 20 can have one or more roughing stands 120, 121, 122. These are arranged one behind the other in the conveying direction of the thin slab strand 115.
  • the number of roughing stands is essentially freely selectable and depends essentially on a format of the thin slab strand 115.
  • a desired thickness of a preliminary strip 125 that the roughing stands 120, 121, 122 roll also plays a role here.
  • three roughing stands 120, 121, 122 are used as an example for the FIG 1 shown roughing mill 20 is provided.
  • the roughing mill 20 is designed to roll the thin slab strand 115, which is hot when fed into the roughing mill 20, into the preliminary strip 125.
  • a first roughing stand 120 is arranged upstream of a second roughing stand 121.
  • a third roughing stand 122 is arranged downstream of the second roughing stand 121.
  • the first separating device 25 and the second separating device 30 are arranged downstream of the roughing train 20 in relation to the conveying direction of the pre-strip 125.
  • the second separating device 30 is arranged at a distance from the roughing train 20 in relation to the conveying direction of the pre-strip 125.
  • a discharge device in FIG 1 not shown in order to convey out a thin slab piece separated by the first separating device 25 and the second separating device 30.
  • the second separating device 30 can also be dispensed with.
  • the first and second separating devices 25, 30 can be designed, for example, as drum shears or pendulum shears.
  • the intermediate heater 45 follows the second separating device 30, for example.
  • the intermediate heater 45 can be designed as an induction furnace, for example. Another design of the intermediate heater 45 would also be possible.
  • the intermediate heater 45 is arranged upstream of the finishing rolling train 55 and the descaler 50 in relation to the conveying direction of the preliminary strip 125.
  • the descaler 50 is arranged directly upstream of the finishing rolling train 55 and downstream of the intermediate heater 45.
  • the descaler 50 can also be dispensed with.
  • the finishing rolling train 55 is arranged downstream of the descaler 50 in relation to the conveying direction of the preliminary strip 125. In the embodiment, the finishing rolling train 55 has five finishing rolling stands 145, 146, 147, 148, 149.
  • the finishing rolling stands 145, 146, 147, 148, 149 are arranged one behind the other in relation to the conveying direction of the preliminary strip 125.
  • the finishing rolling stands 145, 146, 147, 148, 149 roll the preliminary strip 125 fed to the finishing rolling train 55 into a finished strip 165.
  • a first finishing rolling stand 145 is arranged upstream of the other finishing rolling stands 146, 147, 148, 149.
  • a second finishing rolling stand 146 is arranged downstream of the first finishing rolling stand 145 and upstream of a third to fifth finishing rolling stand 147, 148, 149.
  • the third finishing stand 147 is arranged downstream of the second finishing stand 146 and upstream of a fourth finishing stand 148.
  • the fourth finishing stand 148 is arranged downstream of the third finishing stand 147 and upstream of the fifth finishing stand 149.
  • the control unit 75 has a control device 170, a data memory 175 and an interface 180.
  • the data memory 175 is connected by means of a first data connection 185
  • the interface 180 is also connected to the control device 170 via a second data connection 190.
  • a predefined first target temperature, a predefined second target temperature and a predefined third target temperature are preferably stored in the data memory 175. Furthermore, a method for producing the TRIP steel strip 245 is stored in the data memory 175, on the basis of which the control device 170 controls the components of the combined casting and rolling plant 10.
  • the interface 180 is also connected to the intermediate heating system 45 via a third data connection 195.
  • a fourth data connection 200 connects the finishing rolling mill 55 to the interface 180.
  • a fifth data connection 205 connects the cooling section 65 to the interface 180.
  • the combined casting and rolling plant 10 can have a first temperature measuring device 80 and a second temperature measuring device 85.
  • the combined casting and rolling plant 10 can have a third temperature measuring device 172.
  • the first temperature measuring device 80 and/or the second temperature measuring device 85 and/or the third temperature measuring device 172 can be designed as a pyrometer, for example.
  • the first temperature measuring device 80 is arranged downstream of the intermediate heater 45 in relation to the conveying direction of the preliminary strip 125 and is preferably arranged upstream of the descaler 50.
  • the second temperature measuring device 85 is arranged between the cooling section 65 and the finishing rolling train 55.
  • the third temperature measuring device 172 can be arranged in the cooling section 65.
  • the first temperature measuring device 80 is connected to the interface 180 for data purposes by means of a sixth data connection 210.
  • a seventh data connection 215 connects the second temperature measuring device 85 to the interface 180.
  • the third temperature measuring device 172 is connected to the interface 180 by means of an eighth data connection 225.
  • FIG 2 shows one in FIG 1 marked section A of the combined casting and rolling plant 10 in a symbolic representation.
  • the cooling section 65 has a first cooling group 166, a second cooling group 167, at least a third cooling group 168 and preferably a roller conveyor 171.
  • the first cooling group 166 is arranged upstream of the second cooling group 167 in relation to the conveying direction of the finished strip 165.
  • the second cooling group 167 is, for example, directly connected to the first cooling group 166.
  • the third cooling group 168 is arranged directly downstream of the second cooling group 167.
  • the third separating device 35 is arranged subsequent to the third cooling group 168.
  • the first to third cooling groups 166, 167, 168 can each have a plurality of cooling beams 169, wherein the cooling beams 169 are arranged on the top and/or bottom of the finished strip 165.
  • the roller conveyor 171 extends in the conveying direction along the first to third cooling groups 166, 167, 168 in order to transport the finished strip 165 in the cooling section 65 between the finishing rolling mill 55 and the third separating device 35. It is pointed out that a respective length of the cooling group 166, 167, 168 is exemplary. In particular, the length of the cooling group 166, 167, 168 is determined by a transport speed of the finished belt 165. Depending on the transport speed, a length of the respective cooling group 166, 167, 168 can be changed dynamically.
  • the first cooling group 166 is, for example, shorter than the second cooling group 167 and the third cooling group 168. Furthermore, the third cooling group 168 is shorter than the second cooling group 167.
  • the combined casting-rolling plant 10 can have a measuring section 60 which is arranged between the first cooling group 166 and the last first finishing rolling stand 145 with respect to the conveying device of the finished strip 165.
  • FIG 3 shows a diagram of a temperature of the steel between the metallic melt 110 and the TRIP steel strip 245 plotted against time t during the passage through the combined casting and rolling plant 10.
  • FIG 4 shows a flow chart of a method for operating the FIGN 1 and 2 shown combined casting and rolling plant 10.
  • FIG 3 Above the diagram schematically shows the FIG 1
  • the previously explained combined casting and rolling plant 10 is shown in order to be able to easily assign the individual temperatures graphically to the respective component of the combined casting and rolling plant 10.
  • the FIGS are explained together below.
  • the mold 105 of the continuous casting machine 15 is equipped with a cold strand head (not shown in FIG 1 ) and sealed with additional sealing means.
  • the metal melt 110 is filled into the distributor 100 of the continuous casting machine 15 using the ladle 95.
  • the metallic melt 110 preferably has a chemical composition in weight percent of C inclusive of 0.15% up to and including 0.25%, in particular inclusive of 0.19% up to and including 0.21%, Mn 1.0% up to and including 2.0%, in particular 1.4% up to and including 1.6%, Si 1% up to and including 1.5%, in particular 1.1% up to and including 1.3%, Al inclusive of 0.3% up to and including 0.7%, in particular inclusive of 0.45% up to and including 0.55%, the remainder being Fe and unavoidable impurities.
  • the metallic melt 110 can also have a different chemical composition.
  • temperatures and process steps specified below refer to the chemical composition of the steel preferred in the embodiment in order to produce the TRIP steel strip 245 by means of the combined casting and rolling plant 10.
  • the metallic melt 110 in the mold 105 flows around the cold strand head and solidifies at the cold strand head.
  • the cold strand head is slowly drawn out of the mold 105 of the continuous casting machine 15 in the direction of the roughing train 20.
  • the metallic melt 110 in the mold 105 cools at its contact surfaces with the mold 105 and forms a shell of the thin slab strand 115.
  • the shell encloses a liquid core and holds the liquid core.
  • the thin slab strand 115 can, for example, have a thickness of 80 mm to 150 mm.
  • the thin slab strand 115 is deflected and cooled further on the way to the roughing train 20, so that the thin slab strand 115 solidifies from the outside to the inside.
  • the continuous casting machine 15 is designed as an arc continuous casting machine, as explained above, so that by deflecting the thin slab strand 115 by essentially 90° from the vertical, the thin slab strand 115 is fed to the roughing train 20 in an essentially horizontal manner.
  • the thin slab strand 115 is rolled in the roughing mill 20 through the roughing stands 120, 121, 122 to form the preliminary strip 125, as already explained above.
  • a core temperature of the core of the thin slab strand 115 when entering the roughing mill 20 with the above-mentioned chemical composition is approximately 1300 °C to 1450 °C.
  • the core temperature of the core is reduced so that the preliminary strip 125 has a core temperature of approximately 980 °C to 1150 °C when it leaves the roughing mill 20.
  • a thickness reduction of the roughing strip 125 of 35 percent up to and including 60 percent takes place in the roughing pass at the first roughing stand 120 and/or the second roughing stand 121.
  • a thickness reduction of the roughing strip 125 is preferably 35 percent up to and including 50 percent at the third roughing stand.
  • the respective thickness reduction relates to a thickness of the roughing strip 125 when leaving the respective roughing stand 120, 121, 122 to a thickness of the roughing strip 125 when entering the corresponding roughing stand 120, 121, 122. This has the advantage that a thin roughing strip 125 leaves the roughing train 20 at the end of the roughing train 20.
  • a third method step 315 the preliminary strip 125 is guided through the first and second separating devices 25, 30, whereby the preliminary strip 125 is not separated.
  • the preliminary strip 125 is thus only passed through the first and second separating devices 25, 30.
  • the preliminary strip 125 cools further by convection, whereby the cooling during transport to the intermediate heater 45 can be reduced by a protective cover.
  • the control device 170 activates the intermediate heating 45 via the third data connection 195, so that the intermediate heating 45, which is designed as an induction furnace, for example, heats the core temperature of the preliminary strip 125 from 850 °C to 950 °C upon entering the intermediate heating 45 to approximately 1050 °C to 1200 °C. It is particularly advantageous if the preliminary strip 125 leaves the intermediate heating 45 with a core temperature of 1100 °C to 1180 °C. This has the advantage of ensuring optimal hot strip surface quality.
  • the first temperature measuring device 80 which is designed, for example, as a first pyrometer, determines a first surface temperature TO1 of the pre-strip 125 fed from the intermediate heater 45.
  • the first temperature measuring device 80 provides first information about the first surface temperature TO1 of the pre-strip 125 between the intermediate heater 45 and the descaler 50 via the sixth data connection 210 of the interface 180, which provides the first information to the control device 170.
  • a sixth method step 330 the control device 170 regulates a heating power of the intermediate heater 45 such that the determined first surface temperature TO1 of the preliminary strip 125 between the intermediate heater 45 and the descaler 50 essentially corresponds to the first target temperature.
  • the control device 170 can regularly repeat the fifth and sixth method steps 325, 330 in a loop in a predefined time interval.
  • a seventh method step 335 the control device 170 activates the descaler 50 (if present).
  • the descaler 50 descales the preliminary strip 125.
  • the preliminary strip 125 cools down, for example, by 80°C to 100°C relative to the core of the preliminary strip 125. In particular, it can be ensured that when the core temperature is between 1100°C and 1180°C at the outlet from the intermediate heater 45, the descaling performance of the descaler 50 is optimal.
  • the first entry temperature TE1 is related to the core of the preliminary strip 125, with which the preliminary strip 125 enters the first finishing rolling stand 145 in the conveying direction relative to the preliminary strip 125 after the descaler 50.
  • the first entry temperature TE1 can be between 950 °C and 1120 °C, in particular between 950 °C and 1050 °C.
  • the preliminary strip 125 is finish-rolled to the finished strip 165, for example by means of five finishing rolling stands 145. It is particularly advantageous if the thickness of the preliminary strip 125 to the finished rolled strip 165 is reduced by 35 percent up to and including 55 percent in a first finishing rolling pass at the first finishing rolling stand 145. Preferably, the thickness is reduced by 30 percent up to and including 50 percent in the second finishing rolling pass at the second finishing rolling stand 146. Furthermore, the thickness is reduced by 25 percent up to and including 40 percent in the third finishing rolling pass at the third finishing rolling stand 147. Preferably, the thickness is reduced by 20 percent up to and including 30 percent in the fourth finishing rolling pass at the fourth finishing rolling stand 148.
  • a thickness reduction of 10 percent to 20 percent inclusive is preferably carried out in the fifth finishing pass.
  • the thickness reduction therefore takes place primarily at the first to third finishing stands 145, 146, 147, so that a repeated recrystallization of the structure in the finished rolled strip 165 occurs. This is made possible in particular by the high core temperature of 1100°C to 1180°C when leaving the intermediate heating system.
  • the high thickness reduction primarily at the first to third finishing stands 145, 146, 147 is only possible in continuous operation, since only a pull-through condition has to be fulfilled, not a gripping condition. Due to a preferably decreasing thickness reduction in the conveying direction of the finished strip 165 on the first to fifth finishing stands 145, 146, 147, 148, 149, the finished rolled strip is particularly flat when it leaves the finishing rolling mill 55.
  • the finished strip 165 emerges with a thickness of 0.6 mm to 6 mm, in particular 0.8 mm to 2 mm.
  • the preliminary strip 125 to be rolled into the finished strip 165 cools down by approximately 50 °C at each first finishing stand 145 of the finishing train 55, so that the temperature profile (cf. FIG 4 ) forms a stepped line.
  • a first exit temperature TA1 of the finished strip 165 after passing through the finishing rolling mill 55 is approximately 800 °C to 950 °C, in particular from 830 °C to 860 °C inclusive.
  • the first exit temperature TA1 is specified in relation to the core of the finished strip 165.
  • the first exit temperature TA1 can be specifically adjusted using the intermediate heater 45.
  • the first exit temperature TA1 is preferably greater than a ferrite transformation temperature Ar3.
  • the finish rolling via the first finishing rolling stands 145 preferably takes place in an austenitic structure.
  • the first exit temperature TA1 of 830 °C up to and including 860 °C with the core temperature of 1100 °C up to and including 1180 °C at the exit from the intermediate heating 45 a homogeneous, fine-grained austenite can be produced in the finished strip 165 at the exit from the finishing rolling mill 55.
  • the core temperature of 1100 °C up to and including 1180 °C at the exit from the intermediate heating 45 can prevent undesirable fayalite formation (in Si-alloyed steels) and the formation of scale scars on a surface of the finished rolled finished strip 165.
  • the finished strip 165 is transported further in the direction of the cooling section 65 in a tenth process step 350.
  • the finished strip 165 is transported past the second temperature measuring device 85.
  • the second temperature measuring device 85 can be designed as a pyrometer and measures a second surface temperature TO2 of the finished strip 165 coming from the finishing train 55.
  • the second temperature measuring device 85 provides information that correlates with the first exit temperature TA1 to the control device 170 via the seventh data connection 215 and the interface 180.
  • the control device 170 can take the second surface temperature TO2 into account when controlling the intermediate heating 45.
  • the second surface temperature TO2 correlates, as already explained, with the first exit temperature TA1.
  • the second surface temperature TO2 However, its value differs from the first exit temperature TA1.
  • the second surface temperature TO2 refers to the surface of the finished strip 165 and the first exit temperature TA1 refers to the core of the finished strip 165.
  • the finished strip 165 is preferably only 0.6 mm to 6 mm, in particular 0.8 mm to 2 mm thick, the temperature difference between the first exit temperature TA1 and the second surface temperature TO2 is small (less than 10 °C).
  • control of the intermediate heating 45 by the control device 170 is carried out, for example, in such a way that the second surface temperature TO2 essentially corresponds to the second target temperature when controlling the intermediate heating 45.
  • the second temperature measuring device 85 and/or the tenth method step 350 can also be dispensed with.
  • the control device 170 activates the first cooling group 166 via the fifth data connection 205.
  • the finished strip 165 is introduced into the first cooling group 166 with the first exit temperature TA1. Essentially, no phase transformation occurs in the finished strip 165 in the region between a last rolling pass of a last finishing rolling stand and the entry into the first cooling group 166.
  • the first cooling group 166 which preferably has one, in particular several cooling beams 169, a cooling medium, for example water, optionally with an additive, is sprayed onto the hot, finished-rolled finished strip 165 by means of the cooling beams 169.
  • the finished strip 165 is thereby forced-cooled in the first cooling group 166.
  • the core of the finished strip 165 has a predominantly austenitic structure.
  • the phase proportion of the austenitic structure is therefore preferably more than 50%, particularly preferably 100% when it leaves the first cooling group 166.
  • the phase proportion refers to percent by volume.
  • a volume flow of the cooling medium is selected such that within the first cooling group 166 the finished strip 165 is cooled from a second inlet temperature TE2, which essentially corresponds to the first outlet temperature TA1, to a second outlet temperature TA2, of in particular 550 °C to 720 °C, within a first time interval t1 at the first cooling rate.
  • the cooling in the first cooling group 166 takes place in such a way, for example by controlling the volume flow of the cooling medium, that the second outlet temperature TA2 is lower than the Ae3.
  • the second outlet temperature TA2 is between 620 °C and 720 °C inclusive.
  • the flow rate of the cooling medium is selected such that a cooling capacity of the first cooling group 166 ensures a first cooling rate of the core of the finished strip 165 of at least 20 K/s up to and including 1000 K/s, in particular 20 K/s up to and including 500 K/s, in particular 20 K/s up to and including 400 K/s, in particular 50 K/s up to and including 200 K/s.
  • the cooling in the core of the finished strip 165 in the first cooling group 166 preferably takes place continuously via the first cooling group 166.
  • the first cooling speed is ensured, for example, by the fact that a volume flow of approximately 100 m 3 /h to 350 m 3 /h of the cooling medium is sprayed onto the finished strip 165 at a pressure of 2 bar to 4 bar, preferably with the arrangement of several cooling beams 169.
  • This ensures that within the short throughput time of the finished strip 165, for example with a transport speed of 4 m/s to 15 m/s through the first cooling group 166, the core of the finished strip 165 is cooled from the second inlet temperature TE2, for example from 800 °C to 950 °C inclusive, in particular 830 °C to 900 °C, to the second outlet temperature TA2.
  • a control valve can be provided for each cooling beam 169, which the control device 170 can control.
  • the volume flow of the cooling medium can be continuously adjusted between 10% and 100% by the control device 170 for each cooling beam 169 of the first cooling group 166.
  • the finished strip 165 is transported to the second cooling group 167 with the second exit temperature TA2. Transport within the cooling section 65 is carried out by means of the roller conveyor 171.
  • the control device 170 ensures that the second cooling group 167 is deactivated so that no cooling medium is conveyed to the finished strip 165 within the second cooling group 167 and thus no active forced cooling takes place.
  • cooling of the finished strip 165 therefore only occurs through cooling by radiation and convection to the environment of the finished strip 165 within the second cooling group 167.
  • a structure of the finished strip 165 is partially, in particular more than 80 percent phase proportion, particularly preferably completely austenitic, since essentially in the eleventh Process step 355 no or only a slight phase transformation occurs in the finished strip 165.
  • the third temperature measuring device 172 determines a third surface temperature TOS, which correlates with the second exit temperature TA2, after the finished strip 165 exits the first cooling group 166.
  • the third temperature measuring device 172 provides third information about the third surface temperature TO3 via the eighth data connection 225 of the interface 180 and via the interface 180 of the control device 170.
  • the control device 170 can take the information about the third surface temperature TO3 into account when regulating the volume flow of the cooling medium in the first cooling group 166 in the eleventh method step 355.
  • the control device 170 can regulate the volume flow of the cooling medium that is guided, in particular sprayed, from the first cooling group 166 onto the finished strip 165 in such a way that the third surface temperature TO3 essentially corresponds to the third target temperature.
  • the third target temperature is selected in such a way that the second outlet temperature TA2, which relates to the core, lies between the ferrite precipitation temperature Ae3 and the bainite start temperature BS.
  • control device 170 can also take the second surface temperature TO2 into account in order to ensure a uniform first cooling rate in the first cooling group 166.
  • the control device 170 can regularly repeat the eleventh and twelfth method steps 355, 360 in a loop in a predefined time interval.
  • a thirteenth method step 365 the finished strip 165 is transported through the roller conveyor 171 in a warm, partially cooled state in the second cooling group 167 in the direction of the third cooling group 168.
  • the control device 170 keeps the second cooling group 167 in a deactivated state, so that when the finished strip 165 passes through the second cooling group 167, no further cooling medium is applied to the finished strip 165 for further forced cooling of the finished strip 165.
  • the finished strip 165 is cooled via the second cooling group 167 at a second cooling rate from the second exit temperature TA2 to a third exit temperature TA3.
  • the second cooling rate is significantly lower than the first cooling rate.
  • the second cooling rate is, for example, from -25 K/s up to and including 20 K/s, in particular from 0 K/s up to and including 20 K/s.
  • the second cooling rate results primarily from a combined convective and radiative cooling of the finished strip 165 in the second cooling group 167 on the roller conveyor 171. Due to the forced cooling of the finished strip 165 in the eleventh process step 355 below the ferrite start temperature Ae3, a first part of the austenitic structure of the finished strip 165 is converted into ferrite during transport.
  • the finished strip 165 requires a second time interval t2.
  • the second time interval t2 is significantly longer than the first time interval t1.
  • the second time interval t2 can last from 3 seconds to 8 seconds inclusive, in particular from 4 seconds to 5 seconds inclusive.
  • the finished strip 165 passes through the second cooling group 167 and is thus transported from the first cooling group 166 within the second time interval t2 via the second cooling group 167 to the third cooling group 168.
  • the second time interval t2 serves as a holding time. In the second time interval t2, the mixed structure of austenite and ferrite continues to form in the finished strip 165.
  • the proportion of ferrite in the structure of the finished strip 165 increases significantly.
  • the composition of the material of the finished strip 165 is as follows (based on volume percent): 40% to 80% ferrite, in particular 45% to 60% ferrite, the remainder essentially austenite.
  • the homogeneous, fine-grained austenite (cf. ninth process step 345) promotes the rapid formation of the ferrite during passage through the deactivated second cooling group 167. This allows the second cooling group 167 to be kept spatially short.
  • the core of the finished strip 165 has the third exit temperature TA3, which is lower than the second exit temperature TA2.
  • the third exit temperature TA3 is still higher than the austenite-ferrite transformation temperature Ar1.
  • the third exit temperature TA3 can be 580 °C to 710 °C, in particular from 650 °C to 690 °C.
  • the third outlet temperature TA3 corresponds to a third inlet temperature TE3 with which the finished strip 165 enters the third cooling group 168 and is related to the core of the finished strip 165.
  • the cooling of the finished strip 165 in the third cooling group 168 takes place in particular within a third time interval t3.
  • the finished strip 165 is cooled at a third cooling rate that is significantly greater than the second cooling rate.
  • the third cooling rate can be 20 K/s up to and including 1000 K/s, in particular 20 K/s up to and including 500 K/s, in particular 20 K/s up to and including 400 K/s, in particular 50 K/s up to and including 200 K/s.
  • the cooling in the core of the finished strip 165 via the third cooling group 168 preferably takes place continuously.
  • the third cooling rate can be different from the first cooling rate.
  • the finished strip 165 Due to the rapid cooling of the finished strip 165 from the third exit temperature TA3 / third inlet temperature TE3 to the fourth exit temperature TA4, a second portion of the austenite is converted into cementite-free bainite.
  • cementite precipitation is hindered by the alloy components Si and Al, which means that the carbon C remains in solution.
  • the thin-walled design of the finished strip 165 ensures a homogeneous conversion of the austenite into cementite-free bainite across the strip thickness.
  • the control device 170 can activate the third separating device 35 and separate the finished strip 165 so that the wound coil 250 can be removed from the combined casting and rolling plant 10.
  • the finished strip 165 can be continuously conveyed and wound up into another coil 250.
  • the combined casting and rolling plant 10 can additionally have another separating device and further reeling devices 70.
  • An average cooling rate at which the coil 250 cools from the fourth exit temperature TA4 to the ambient temperature TU can preferably be 3 K/h up to and including 15 K/h, so that, for example, the coil 250 is cooled in a fourth time interval t4 of approximately 24 hours to 72 hours.
  • the heat hood allows the Coil 250 (both on the inner winding and/or the outer winding and/or the middle winding) to be cooled at a sixth cooling rate of 1 K/h up to and including 10 K/h in the first hour after coiling. under the heat hood.
  • the average cooling rate can be from the fourth outlet temperature TA4 preferably inclusively 1 K/h up to and including 8 K/h under the heat hood.
  • the heat hood is removed in a seventeenth method step 385 and further cooling of the coil 250 takes place through the environment of the coil 250 to the ambient temperature TU.
  • the average cooling rate after removal of the heat hood can be 2 K/h to 12 K/h inclusive.
  • the use of the heat hood has the advantage that the TRIP steel strip 245 has a particularly homogeneous structure and therefore particularly homogeneous material properties.
  • the production of the finished strip 165 is completed and the cooled finished strip 165 is now formed as TRIP steel strip 245. If the TRIP steel strip 245 is deformed mechanically in the subsequent production process, for example due to a traffic accident or in a press, the metastable residual austenite forms martensite during deformation.
  • the TRIP steel strip 245 has the following chemical composition: from 0.15% to 0.25% inclusive, in particular from 0.19% to 0.21% inclusive, Mn 1.0% to 2.0% inclusive, in particular from 1.4% to 1.6%, Si 1.0% to 1.5% inclusive, in particular from 1.1% to 1.3%, Al inclusive from 0.3% to 0.7% inclusive, in particular from 0.45% to 0.55%, balance Fe and unavoidable impurities.
  • the TRIP steel strip 245 has the following microstructure at ambient temperature TU (based on volume percent): from 40% to 60% ferrite, in particular from 45% to 55% ferrite, from 8% to 15% metastable residual austenite and, preferably, cementite-free bainite.
  • the TRIP steel strip 245 can be produced with a particularly low thickness, in particular 0.6 mm to 6 mm, in particular 0.8 mm to 2 mm, in a continuous casting-rolling composite directly without cold rolling and annealing. This has the advantage that the energy required to produce the TRIP steel strip 245 is significantly lower and thus the TRIP steel strip 245 can be produced in a more environmentally friendly and cost-effective manner.
  • the holding time which corresponds to the second time interval t2
  • the holding time which corresponds to the second time interval t2
  • the holding time which corresponds to the second time interval t2 between the exit of the finished strip 165 from the first cooling group 166 to the entry into the third cooling group 168 is ensured to be from 3 seconds to 8 seconds, in particular from 4 seconds to 5 seconds.
  • a sufficiently large proportion of ferrite is present in the finished strip 165 at the end of the second cooling group 167.
  • the above-described design of the combined casting-rolling plant 10 with the above-described method allows a high casting speed of 0.08 m/s to 0.1 m/s to be achieved with the specified thickness of the thin slab strand 115 of 100 mm to 150 mm.
  • the combined casting and rolling plant 10 can also be designed differently than described in the figures.
  • the combined casting and rolling plant 10 it would also be possible for the combined casting and rolling plant 10 to have, for example, six finishing stands 145, with the last finishing stand 145 in the conveying direction being converted into a stand cooler in a preparation step.
  • work rolls can be removed from the finishing stand 145 by opening a changing device and replaced by one or more cooling beams.
  • the cooling beam of the stand cooler can be aligned so that it is directed directly in the direction of a passage through which the finished strip 165 is guided. When the changing device is closed, the cooling beams are fastened in the stand cooler.
  • the cooling section 65 is extended against the conveying direction of the finished strip and the stand cooler forms a section of the first cooling group 166.
  • an intermediate cooler could also be arranged between the finishing rolling stand 145 and the stand cooler.
  • the casting and rolling plant 10 and the FIG 3 TRIP steel strip 245, manufactured in continuous strands using the process described above, is particularly suitable for the manufacture of vehicle body panels and has particularly good material properties.
  • the increase in strength during forming is particularly suitable for highly stressed components, in particular crash body components of motor vehicles.
  • the transformation of metastable austenite into martensite occurs primarily during a crash, whereby the increase in strength during forming at high elongation at break allows a lot of energy to be dissipated.
  • the TRIP steel band 245 is suitable for vehicle components.
  • the TRIP steel band 245 and the components made with it are particularly tough and strong.
  • the casting-rolling composite plant 10 has a particularly precise and stable process control due to the continuous operation and the direct production of the TRIP steel strip 245, so that a high level of homogeneity of the hot strip is ensured. Since cold rolling and annealing can be dispensed with in the direct production of the TRIP steel strip 245 in continuous operation of material of the finished strip 165 that has already cooled to ambient temperature, the energy required to produce the TRIP steel strip 245 is particularly low.

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EP23164462.6A 2023-03-27 2023-03-27 Procédé de fabrication directe d'une bande d'acier trip dans une installation composite de coulée-laminage et bande d'acier trip ainsi fabriquée Pending EP4438746A1 (fr)

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EP23164462.6A EP4438746A1 (fr) 2023-03-27 2023-03-27 Procédé de fabrication directe d'une bande d'acier trip dans une installation composite de coulée-laminage et bande d'acier trip ainsi fabriquée
US18/411,282 US20240327944A1 (en) 2023-03-27 2024-01-12 Process for direct production of a trip steel strip in an integrated casting-rolling plant and a trip steel strip produced by the process
CN202480021640.2A CN120858185A (zh) 2023-03-27 2024-03-22 在联合铸轧设备中直接生产trip钢带的方法
PCT/EP2024/057783 WO2024200274A1 (fr) 2023-03-27 2024-03-22 Procédé de production directe d'une bande d'acier trip dans une installation de combinaison de coulée-laminage

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0952235A1 (fr) * 1996-11-28 1999-10-27 Nippon Steel Corporation Plaque d'acier a haute resistance mecanique dotee d'une forte resistance a la deformation dynamique et procede de fabrication correspondant
EP1045737A1 (fr) 1997-12-08 2000-10-25 Corus Staal BV Procede et dispositif de production d'une bande d'acier haute resistance
EP3206808A1 (fr) * 2014-10-16 2017-08-23 SMS group GmbH Installation et procédé de fabrication de tôles fortes
EP4101552A1 (fr) * 2021-06-09 2022-12-14 Primetals Technologies Austria GmbH Procédé de fabrication d'acier micro-allié, acier micro-allié fabriqué selon le procédé et installation combinée de coulée et de laminage

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0952235A1 (fr) * 1996-11-28 1999-10-27 Nippon Steel Corporation Plaque d'acier a haute resistance mecanique dotee d'une forte resistance a la deformation dynamique et procede de fabrication correspondant
EP1045737A1 (fr) 1997-12-08 2000-10-25 Corus Staal BV Procede et dispositif de production d'une bande d'acier haute resistance
EP3206808A1 (fr) * 2014-10-16 2017-08-23 SMS group GmbH Installation et procédé de fabrication de tôles fortes
EP4101552A1 (fr) * 2021-06-09 2022-12-14 Primetals Technologies Austria GmbH Procédé de fabrication d'acier micro-allié, acier micro-allié fabriqué selon le procédé et installation combinée de coulée et de laminage

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