Method for the production of hot strip or sheet from a micro-alloyed steel

Abstract

The invention relates to a method for producing hot strip or hot plate, in which a microalloyed steel, which, apart from microalloying elements, comprises (in weight %) C: 0.05-0.12%; Si:0.2-0.5%; Mn:1.5-2.2 %; Al:0.02-0.05%; P:≦0.025%; S:≦0.01%; with the remainder being iron and unavoidable impurities, is cast to form a raw material such as slabs, blooms or thin slabs; in which the raw material is heated to a temperature of 1300-1350° C.; in which the heated raw material is rough rolled at a degree of deformation of 36% to 43%; in which the rough rolled raw material is thermomechanically hot rolled at a final rolling temperature which exceeds the Ac 3 temperature so as to form a hot strip; in which the hot strip is cooled at a cooling rate of at least 15° C./s to a coiling temperature of at least 590° C. and at most 630° C. at which temperature the cooled hot strip is finally coiled. With such a method, hot strip which is of particularly high strength even at larger thicknesses can be produced economically.

1 . A method for producing hot strip or hot plate 
 in which a microalloyed steel which, apart from microalloying elements, comprises (in weight %)                                                C:   0.05-0.12%;         Si:    0.2-0.5%;         Mn:    1.5-2.2%;         Al:   0.02-0.05%;         P:   ≦0.025%;         S:   ≦0.01%                                                  with the remainder being iron and unavoidable impurities, is cast to form a raw material such as slabs, blooms, or thin slabs;    in which the raw material is heated to a temperature of 1300-1350° C.;    in which the heated raw material is rough rolled at a degree of deformation of 36% to 43%;    in which the rough rolled raw material is thermomechanically hot rolled at a finish roll temperature which exceeds the Ac 3  temperature so as to form a hot strip;    in which the hot strip is cooled at a cooling rate of at least 15° C./s to a coiling temperature of at least 590° C. and at most 630° C.;    at which temperature the cooled hot strip is finally coiled.    
     
     
         2 . The method according to  claim 1 , characterised in that the steel comprises at least one of the microalloying elements V, Mo, Ti, Nb in the following percentages (in weight %):  
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                     
                 
                     
                   V: 
                   0.08-0.12%; 
                 
                     
                   Mo: 
                   0.1-0.2%; 
                 
                     
                   Ti: 
                   0.08-0.11%; 
                 
                     
                   Nb: 
                   0.05-0.06%. 
                 
                     
                     
                 
                     
                     
                 
             
                
                
               
               
                
                
                
                
                
                
               
            
           
         
       
     
     
         3 . The method according to any one of the preceding claims, characterised in that at a thickness exceeding 8 mm, the hot strip or hot plate has a minimum yield point of 700 N/mm 2 .  
     
     
         4 . The method according to any one of the preceding claims, characterised in that the steel comprises (in weight %):  
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                     
                 
                     
                   C: 
                   0.06-0.08%; 
                 
                     
                   Si: 
                    0.2-0.3%; 
                 
                     
                   Mn: 
                   1.95-2.1%; 
                 
                     
                   Al: 
                   0.02-0.05%; 
                 
                     
                   P: 
                   ≦0.02%; 
                 
                     
                   S: 
                   ≦0.005%. 
                 
                     
                     
                 
                     
                     
                 
             
                
                
               
               
                
                
                
                
                
                
                
                
               
            
           
         
       
     
     
         5 . The method according to  claim 4 , characterised in that the Ti content does not exceed 0.1 weight %.  
     
     
         6 . The method according to any one of  claims 1  to  3 , characterised in that the steel comprises (in weight %):  
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                     
                 
                     
                   C: 
                   0.10-0.12%; 
                 
                     
                   Si: 
                    0.4-0.5%; 
                 
                     
                   Mn: 
                   1.95-2.1%; 
                 
                     
                   Al: 
                   0.02-0.05%; 
                 
                     
                   P: 
                   ≦0.02%; 
                 
                     
                   S: 
                   ≦0.005%. 
                 
                     
                     
                 
                     
                     
                 
             
                
                
               
               
                
                
                
                
                
                
                
                
               
            
           
         
       
     
     
         7 . The method according to  claim 6 , characterised in that the steel comprises at least one of the microalloying elements V, Mo, Ti, Nb in the following percentages (in weight %)  
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                     
                 
                     
                   V: 
                   0.08-0.10%; 
                 
                     
                   Mo: 
                   0.1-0.2%; 
                 
                     
                   Ti: 
                   0.09-0.11%; 
                 
                     
                   Nb: 
                   0.05-0.06%. 
                 
                     
                     
                 
                     
                     
                 
             
                
                
               
               
                
                
                
                
                
                
               
            
           
         
       
     
     
         8 . The method according to  claim 6  or  7 , characterised in that at a thickness of 13 mm, the hot strip or hot plate has a minimum yield point of 760 N/mm 2 .  
     
     
         9 . The method according to any one of the preceding claims, characterised in that slabs are used as raw material, with the holding time during heating of the slabs being at least 135 minutes.  
     
     
         10 . The method according to any one of the preceding claims, characterised in that the final rolling temperature is at least 840° C.  
     
     
         11 . The method according to any one of the preceding claims, characterised in that the coiling temperature is at least 600° C. and at most 620° C.  
     
     
         12 . The method according to any one of the preceding claims, characterised in that the steel optionally comprises one or several of the elements N, Cu, Ni, Sn, B or As, wherein the total content of these elements does not exceed 0.1 weight %.