Method For Producing A Cast Steel Strip

Abstract

The invention relates to a method for producing a cast steel strip of preferably hot crack-sensitive or hot-brittle steel quality by means of a strip casting plant and to a strip casting plant for carrying out this method. In this case, steel melt is conducted into a melt space formed by two casting rolls and two sideplates, slab shells are formed in the melt space on cooled surface areas of the casting rolls and are brought together in the strip forming cross section between the casting rolls to form an at least partly solidified steel strip, the cast steel strip is then guided along the surface area of one of the two casting rolls from a vertical casting direction into an essentially horizontal transport direction, and the cast steel strip is supplied essentially horizontally on a transport device to a strip winding device and is wound there into a coil. In order in this case to minimize susceptibility to crack formation, the cast steel strip, during its transport movement along the surface area of one of the two casting rolls, is guided in a transport channel without the application of deformation forces influencing the strip thickness and is subjected in this region to strip cooling of less than 200 K/s.

1 . A method for producing a cast steel strip by a strip casting plant, comprising
 conducting steel melt into a melt space formed by and between two casting rolls and by and between two sideplates at the rolls,   forming slab shells in the melt space by cooling surface areas of the casting rolls and bringing the slab shells together in a strip forming cross section between the casting rolls to form an at least partly solidified steel strip,   guiding the cast steel strip along the surface area of one of the two casting rolls from a vertical casting direction out of the melt space into an essentially horizontal transport direction and away from the one casting roll, and   transporting the cast steel strip being supplied essentially horizontally on a transport device to a strip winding device and there winding the strip into a coil,   during transport of the cast steel strip, along the surface area of the one of the two casting rolls, guiding the strip in a transport channel with the local application of pressure forces, and, in the transport channel, cooling the strip in a range of 15 K/s to 200 K/s, and setting in a strip tension in the region of a lower vertex of the one casting roll to a value at which the steel strip bears against the casting roll, essentially free of slip, over essentially the entire arc of a quarter circle around the one casting roll.   
     
     
         2 . The method as claimed in  claim 1 , wherein during transport movement of the cast steel strip along one of the surface areas of the casting rolls, the strip is guided in an atmosphere with an oxygen content reduced in respect
 of air or in a largely oxygen-free protective gas atmosphere.   
     
     
         3 . The method as claimed in  claim 2 , wherein the oxygen content of the atmosphere is set at less than 8% oxygen. 
     
     
         4 . The method as claimed in  claim 1 , wherein after the cast steel strip runs through the transport channel and moves in translation away from the surface area of the casting roll, the strip is guided essentially horizontally over a distance of at least 1 m. 
     
     
         5 . The method as claimed in  claim 1 , wherein after the cast steel strip transports essentially horizontally, permitting the strip to form a strip loop, and, starting from this strip loop, introducing a reacting strip tension into the cast steel strip. 
     
     
         6 . The method as claimed in  claim 5 , further comprising controlling or regulating a strip tension in the cast steel strip in the region of the lower vertex of the casting roll by the dead weight of the strip loop. 
     
     
         7 . The method as claimed in  claim 1 , wherein during an essentially horizontal transport movement, including strip tensile stresses or strip compressive stresses reacting as far as the casting roll into the steel strip by applying a clamping force along a path segment to the end of the transport in the transport direction of the steel strip. 
     
     
         8 . The method as claimed in  claim 7 , further comprising setting a strip tension in the cast steel strip by of applying a clamping force to the steel strip. 
     
     
         9 . The method as claimed in  claim 1 , wherein a mean strip cross-section temperature at the end of a first essentially horizontal transport movement of the metal strip is 60° C. to 250° C. lower than in the strip forming cross section. 
     
     
         10 . The method as claimed in  claim 1 , wherein the essentially horizontal transport movement of the steel strip comprises deviations of +/−15° with respect to the horizontal. 
     
     
         11 . The method as claimed in  claim 1 , further comprising subjecting the cast steel strip to an at least single-step strip thickness reduction before winding up the strip in the strip winding device. 
     
     
         12 . The method as claimed in  claim 1 , further comprising before starting a casting operation, introducing, a cold strip into the strip casting plant close the strip forming cross section between the casting rolls and extend in the strip transport direction or on an essentially horizontally oriented transport device or up to and above a loop pit and there separating the cold strip from the cast steel strip. 
     
     
         13 . The method as claimed in  claim 1 , further comprising starting a casting operation without a dummy slab, conveying a first portion of the cast steel strip out of the transport channel in a vertical movement and, under a load of the dead weight of the first portion in the strip forming cross section or in the transport channel shortly after the strip forming cross section, separating the first portion from the following steel strip, and conducting the following cast steel strip along the surface area of one of the two casting rolls and in a transport channel and into an essentially horizontal transport direction. 
     
     
         14 . A strip casting plant for producing a cast steel strip of predetermined strip thickness comprising two rotary-driven casting rolls having internally cooled surface areas and two sideplates which can be pressed against ends of the casting rolls to jointly form a melt space for the reception of steel melt and a strip forming cross section for the steel strip to be cast, an essentially horizontally oriented transport device for the steel strip deflected along one of the surface areas and out of the vertical casting direction into an essentially horizontal transport direction, and a following strip winding device a strip guide device at one of the two casting rolls cooperating with the surface area of the casting roll to form a transport channel for the cast steel strip, and the two the cooperating casting rolls include internal cooling devices activatable independently of one another, an insulating chamber in which the transport channel for the cast steel strip is arranged for maintaining a predetermined atmosphere, and
 either the transport device comprises rollers with rotational speed regulation for setting a strip tension in the region of the lower vertex of the casting roll,   or a strip store with a position measurement device adjoins the essentially horizontally oriented transport device such that the dead weight of the strip loop sets a strip tension in the region of the lower vertex of the casting roll.   
     
     
         15 . The strip casting plant as claimed in  claim 14 , the further comprising a strip guide device at one of the two casting rolls and between the strip forming cross section and the transport device, and supporting elements of the strip guide device are arranged according to the strip thickness at an essentially equal distance from the surface area of the casting roll and the guide device cooperates with the surface area of the one casting roll to form a transport channel for the cast steel strip. 
     
     
         16 . The strip casting plant as claimed in  claim 14 , wherein the transport channel for the cast steel strip forms, at least in a part region, a wall element of the insulating chamber. 
     
     
         17 . The strip casting plant as claimed in  claim 14 , wherein the strip guide device forms, in a part region, a structural unit with wall elements of the insulating chamber. 
     
     
         18 . The strip casting plant as claimed in  claim 14 , wherein the transport channel for the cast steel strip covers an arc of essentially a quarter circle along the surface area of the one casting roll. 
     
     
         19 . The strip casting plant as claimed in  claim 14 , wherein the transport channel has a clear width equal to or greater than the thickness of the cast strip. 
     
     
         20 . The strip casting plant as claimed in  claim 14 , further comprising supporting elements of the strip guide device are formed by nondriven supporting rolls. 
     
     
         21 . The strip casting plant as claimed in  claim 14 , wherein vertically below the strip forming cross section formed by the casting rolls or below the casting roll coforming the transport channel, operable for closing the passage orifice for a dummy piece of the cast steel strip, and a closing device operable for closing the passage orifice. 
     
     
         22 . The strip casting plant as claimed in  claim 14 , further comprising cooling devices operable for cooling one the thermally loaded components of the strip guide device ( 17 ). 
     
     
         23 . The strip casting plant as claimed in  claim 14 , wherein the essentially horizontally oriented transport device has a longitudinal extent of at least 1 m. 
     
     
         24 . The strip casting plant as claimed in  claim 14 , wherein the transport device is arranged at an inclination of up to +/−15° with respect to the horizontal. 
     
     
         25 . The strip casting plant as claimed in  claim 14 , wherein the strip store comprises a loop pit. 
     
     
         26 . The strip casting plant as claimed in  claim 14 , wherein the strip store comprises an entry region into the strip store and an exit region out of the strip store, and the exit region out of the strip store is lower than and with respect to the entry region into the strip store. 
     
     
         27 . The strip casting plant as claimed in  claim 26 , further comprising a bridging chute pivotable inward and outward arranged between the entry region into the strip store and the exit region out of the strip store. 
     
     
         28 . The strip casting plant as claimed in  claim 26 , further comprising a continuous or segmented insulating chamber surrounding the transport path of the steel strip in the strip casting plant and arranged between the casting rolls and the exit region out of the strip store. 
     
     
         29 . The strip casting plant as claimed in  claim 14 , further comprising at least one roll stand preceding the strip winding device in the transport direction and a strip deflection device at the at least one roll stand. 
     
     
         30 . The strip casting plant as claimed in  claim 29 , further comprising a continuous insulating chamber surrounding the transport path of the steel strip in the strip casting plant and arranged between the casting rolls and a first one of the roll stands. 
     
     
         31 . The strip casting plant as claimed in  claim 21 , wherein the closing device comprises a flap pivotable about a horizontal axis. 
     
     
         32 . The strip casting plant as  claim 23 , wherein the transport device has a longitudinal extent of at least 2 m. 
     
     
         33 . The method as claimed in  claim 3 , wherein the atmosphere is set of less than 1.0% oxygen. 
     
     
         34 . The method as claimed in  claim 4 , wherein the strip is guided essentially horizontally for more than 2 m. 
     
     
         35 . The method as claimed in  claim 8 , wherein the strip tension is set in a region of the lower vertex of the casting roll.