Method and device for producing a microalloyed steel, in particular a pipe steel

Abstract

The invention relates to a method of making microalloyed steel, in particular a pipe steel, wherein a cast slab ( 1 ) passes through an installation ( 2 ) having a casting machine ( 3 ), a first furnace ( 4 ), at least one roughing roll stand ( 5 ), a second furnace ( 6 ), at least one finishing roll stand ( 7 ), and a cooling line ( 8 ) in this order in the travel direction (F) of the slab ( 1 ). The method comprises: a) definition of a desired temperature profile for the slab ( 1 ) over its travel through the installation ( 2 ); positioning in the process line (L) of the installation ( 2 ) at least one temperature-influencing element ( 9, 10 ) for setting the temperature of the slab ( 1 ) according to the defined temperature profile, the temperature-influencing element ( 9, 10 ) being introduced between the first furnace ( 4 ) and the roughing roll stand ( 5 ), and/or between the second furnace ( 6 ) and the finishing roll stand ( 7 ); production of the slab ( 1 ) in the installation ( 2 ) configured in this manner, the temperature-influencing element ( 9, 10 ) being operated in such a way that the defined temperature profile is at least substantially maintained. The invention further relates to an installation for making microalloyed steel.

1 - 26 . (canceled) 
     
     
         27 . A method of making microalloyed steel, in particular pipe steel, wherein a cast slab passes through an installation having a casting machine, a first furnace, at least one roughing roll stand, a second furnace, at least one finishing roll stand, and a cooling line in this order in a travel direction of the slab, the method comprising:
 a) definition of a desired temperature profile for the slab over its travel through the installation;   b) positioning in the process line of the installation at least one temperature-influencing element for setting the temperature of the slab according to the defined temperature profile, the temperature-influencing element being provided between the first furnace and the roughing roll stand, or between the second furnace and the finishing roll stand;   c) production of the slab or strip in the installation configured in this manner, the temperature-influencing element being operated in such a way that the defined temperature profile is at least substantially maintained,   
       wherein by use of a temperature-influencing element in the form of a cooler, an input temperature may be achieved in the finishing roll stand that is low enough that the recrystallization and grain growth at that location are largely halted, the temperature level between the input into the roughing roll stand and the input into the temperature-influencing element in the form of a cooler being either
 aa) decreased, in particular for pipe steel having a low microalloy element content and small slab thickness, by a temperature-influencing element in the form of a cooler in order to reduce the grain size upon entry into the finishing roll stand, or 
 bb) increased, in particular for pipe steel having a high microalloy element content and large slab thickness, by a temperature-influencing element in the form of a heater to ensure complete recrystallization during roughing, or 
 cc) merely balanced and otherwise being left unchanged, or 
 
       by use of a temperature-influencing element in the form of a heater, an input temperature is achieved in the finishing roll stand that is high enough that complete recrystallization takes place at that location, either
 Aa) during the first finishing passes due to the high temperatures and reductions, followed by an accumulation of deformation in the last finishing passes, or 
 Bb) only during the last finishing passes due to moderate temperatures and reductions, after prior accumulation of deformation has taken place. 
 
     
     
         28 . The method defined in  claim 27 , wherein an additional furnace is used as the temperature-influencing element. 
     
     
         29 . The method defined in  claim 28 , wherein an induction furnace is used as the additional furnace. 
     
     
         30 . The method defined in  claim 28 , wherein in the additional furnace the slab is heated by direct flame action. 
     
     
         31 . The method defined in  claim 30 , wherein the direct flame action of the slab is provided by a gas jet containing 75% oxygen and a gaseous or liquid fuel. 
     
     
         32 . The method defined in  claim 28 , wherein a soaking furnace is used as the additional furnace. 
     
     
         33 . The method defined in  claim 28 , wherein a roller hearth furnace is used as the additional furnace. 
     
     
         34 . The method defined in  claim 28 , wherein a walking-beam furnace or a pusher-type furnace that allows transverse transport of the slab is used as the additional furnace. 
     
     
         35 . The method defined in  claim 27 , wherein an additional cooling line is used as the temperature-influencing element. 
     
     
         36 . The method defined in  claim 35 , wherein an intensive cooler is used as the additional cooling line. 
     
     
         36 . The method defined in  claim 35 , wherein a laminar strip cooler is used as the additional cooling line. 
     
     
         37 . The method defined in  claim 27 , wherein a thermally insulating element is used as the temperature-influencing element. 
     
     
         38 . The method defined in  claim 27 , wherein the temperature profile is determined on the basis of a structural model. 
     
     
         39 . The method defined in  claim 38 , wherein the structural model specifies or monitors the following parameters: the temperature profile over time or the number of passes, the reduction distribution over time or the number of passes, the holding or cycle times, the roller speeds and transport speeds, or the heating and cooling intensities.