Hot rolling method and hot rolling line

Abstract

A hot rolling line and a hot rolling method capable of finer refining crystal grains are provided. Specifically, the hot rolling line for a metal sheet is composed of a finish rolling mill, a leveler, and a cooling apparatus installed from upstream to downstream in this sequence in a metal sheet transporting direction. The hot rolling method is such that, in the above hot rolling line, a metal sheet obtained by finish rolling a metal piece is subjected to repeated bending processing by the leveler and then cooled.

1 . A hot rolling line for a metal sheet, characterized in that a finish rolling mill, a leveler for adding bending strain to the metal sheet, and a cooling apparatus are installed in this sequence from upstream to downstream in the transporting direction of the metal sheet.  
     
     
         2 . A hot rolling line for a metal sheet, characterized in that a finish rolling mill, a leveler in which work rolls are backed up by back-up rolls, respectively, and a cooling apparatus are installed in this sequence from upstream to downstream in the transporting direction of the metal sheet.  
     
     
         3 . A hot rolling line for a metal sheet, characterized in that a finish rolling mill, a cooling apparatus, a leveler, and an additional cooling apparatus, are installed in this sequence from upstream to downstream in the transporting direction of the metal sheet.  
     
     
         4 . A hot rolling line for a metal sheet, characterized in that a finish rolling mill, a cooling apparatus, a leveler in which work rolls are backed up by back-up rolls, respectively, and further a cooling apparatus are installed in this sequence from upstream to downstream in the transporting direction of the metal sheet.  
     
     
         5 . A hot rolling line for a metal sheet, characterized in that a joint apparatus, a finish rolling mill, a leveler for adding bending strain to the metal sheet, a cooling apparatus, a shearing apparatus, and a coiler are installed in this sequence from upstream to downstream in the transporting direction of the metal sheet.  
     
     
         6 . A hot rolling line for a metal sheet, characterized in that a joint apparatus, a finish rolling mill, a leveler in which work rolls are backed up by back-up rolls, respectively, a cooling apparatus, a shearing apparatus, and a coiler are installed in this sequence from upstream to downstream in the transporting direction of the metal sheet.  
     
     
         7 . A hot rolling line for a metal sheet, characterized in that a joint apparatus, a finish rolling mill, a cooling apparatus, a leveler, further a cooling apparatus, a shearing apparatus, and a coiler are installed in this sequence from upstream to downstream in the transporting direction of the metal sheet.  
     
     
         8 . A hot rolling line for a metal sheet, characterized in that a joint apparatus, a finish rolling mill, a cooling apparatus, a leveler in which work rolls are backed up by back-up rolls, respectively, an additional cooling apparatus, a shearing apparatus, and a coiler are installed in this sequence from upstream to downstream in the transporting direction of the metal sheet.  
     
     
         9 . A hot rolling line according to any of  claims 1  to  8 , characterized in that the leveler has work rolls whose diameter is set to 300 mm or less.  
     
     
         10 . A hot rolling line according to any of  claims 1  to  8 , characterized in that the leveler is a lever having 3 to 30 of work rolls.  
     
     
         11 . A hot rolling line according to any of  claims 1  to  8 , characterized in that a drive system is employed in the respective work rolls of the leveler.  
     
     
         12 . A hot rolling line according to any of  claims 1  to  8 , characterized in that guides are disposed in the intervals between the respective work rolls of the upper and lower work rolls of the leveler.  
     
     
         13 . A hot rolling line according to any of  claims 1  to  8 , characterized in that the surface roughness Ra of the work rolls of the leveler is set to 0.5<Ra<2.0 μm.  
     
     
         14 . A hot rolling line according to any of  claims 1  to  8 , characterized in that the leveler has at least one small diameter work roll whose diameter is set to less than 40 times the thickness of the finish-rolled metal sheet.  
     
     
         15 . A hot rolling line according to any of  claims 1  to  8 , characterized in that the leveler has at least one non-driven small diameter work roll whose diameter is set to less than 40 times the thickness of the finish-rolled metal sheet and the remaining work rolls have a diameter set to 40 times or more the thickness of the finish-rolled metal sheet as well as can be driven.  
     
     
         16 . A hot rolling line according to any of  claims 1  to  8 , characterized in that the leveler has at least one non-driven small diameter work roll whose diameter is set to less than 40 times the thickness of the finish-rolled metal sheet, the small diameter work roll is arranged such that it has a back-up roll and drive torque is transmitted from the back-up roll to the small diameter work roll through the gears disposed to the respective necks of the small diameter work roll and the back-up roll, and the remaining work rolls have a diameter set to 40 times or more the thickness of the finish-rolled metal sheet and can be driven.  
     
     
         17 . A hot rolling method of subjecting a metal piece to hot rolling including finish rolling, characterized in that a metal sheet, which has been subjected to the finish rolling, is subjected to repeated bending processing by a leveler and then cooled.  
     
     
         18 . A hot rolling method according to  claim 17 , characterized in that the metal sheet having been subjected to the finish rolling is cooled before the metal sheet is subjected to the repeated bending processing.  
     
     
         19 . A hot rolling method according to  claim 17  or  18 , characterized in that the temperature of the metal sheet having been subjected to the repeated bending processing is set within the range from the Ar 3  point +50° C. to the Ar 3  point −100° C.  
     
     
         20 . A hot rolling method according to  claim 17  or  18 , characterized in that the amount of push of the work rolls of the leveler is set to +1 to +30 mm.  
     
     
         21 . A hot rolling method according to  claim 17  or  18 , characterized in that the temperature of the finish-rolled metal sheet is set to the Ar 3  point or higher.  
     
     
         22 . A hot rolling method according to  claim 17  or  18 , characterized in that the transportation of the leading end and the tailing end of the metal sheet is tracked, and control is performed such that upper and lower work rolls are tightened after the leading end of the metal sheet has passed through the upper and lower rolls of the leveler and the upper and lower rolls are opened before the tailing end of the metal sheet leaves the upper and lower rolls.  
     
     
         23 . A hot rolling method according to  claim 17  or  18 , characterized in that the finish rolling is performed after a preceding sheet bar has been joined to a succeeding sheet bar.