Strip of steel having a variable thickness in length direction

Abstract

A strip of steel having a variable thickness in its length direction with at least thicker and thinner sections, the strip having been cold rolled to form the thicker and thinner sections, one thicker and one thinner section having a length of at most a few meters, which strip has been annealed. The annealing has been performed by continuous annealing.

1 . Strip of steel having a variable thickness in its length direction with at least thicker sections and thinner sections such that the strip has a repetitive thickness variation, the strip having been cold rolled to form the thicker and thinner sections, one thicker and one thinner section having a length of at most a few meters, which strip has been annealed, wherein the strip is to be cut into pieces called tailor rolled blanks, wherein the annealing has been performed by continuous annealing. 
     
     
         2 . Strip of steel according to  claim 1 , wherein the yield strength of the thicker sections is equal to or higher than the yield strength of the thinner sections. 
     
     
         3 . Strip of steel according to  claim 1 , wherein the steel strip is a Dual Phase steel, TRIP steel or multi phase high strength steel. 
     
     
         4 . Strip of steel according to  claim 1 , wherein the steel strip is a HSLA steel or a low carbon steel. 
     
     
         5 . Strip of steel according to  claim 4 , wherein only the thinner sections are recrystallised and wherein the difference in yield strength of the thicker and thinner sections is smaller than in the same HSLA or low carbon steel strip that has been batch annealed. 
     
     
         6 . Strip of steel according to  claim 4 , wherein the composition of the steel has lower values of alloying elements than in a batch annealed HSLA or low carbon steel having the same yield strength of the thinner sections. 
     
     
         7 . Strip of steel according to  claim 4 , wherein the steel has the following composition in wt %: 
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                   C 
                   0.03 to 0.08 
                 
                     
                   Mn 
                   0.1 to 1.2 
                 
                     
                   Si 
                   ≦1.0 
                 
                     
                   P 
                   ≦0.1 
                 
                     
                   Nb 
                   ≦0.07 
                 
                     
                   V 
                   ≦0.5 
                 
                     
                   Ti 
                   ≦0.1 
                 
                     
                     
                 
             
                
               
               
                
                
                
                
                
                
                
                
               
            
           
         
       
       the remainder being iron and inevitable impurities. 
     
     
         8 . Strip of steel according to  claim 7 , wherein the steel is characterized by the equation: YS≧250+225(Mn/6+Si/24)+716P+2938Nb+600V+2000Ti [MPa] with Mn, Si, P, Nb, V, Ti in wt % and YS being the yield strength in the thinner sections of the strip. 
     
     
         9 . Strip of steel according to  claim 8 , wherein YS≧270+225(Mn/6+Si/24)+716P+2938Nb+600V+2000Ti [MPa]. 
     
     
         10 . Strip of steel according to  claim 4 , wherein
     A 80 ≧−0.05*YS+40   with A80 being the total elongation in the thinner sections of the strip and YS being the yield strength in the thinner sections of the strip.   
     
     
         11 . Strip of steel according to  claim 1 , wherein the steel in the thinner sections has a tensile strength above 600 MPa and a yield strength below 400 MPa. 
     
     
         12 . Strip of steel according to  claim 11 , wherein the steel in the thinner sections has a tensile strength above 600 MPa and a yield strength below 300 MPa. 
     
     
         13 . Strip of steel according to  claim 1 , wherein the steel in the thinner sections has a tensile strength above 800 MPa and a yield strength below 550 MPa. 
     
     
         14 . Strip of steel according to  claim 13 , wherein the steel in the thinner sections has a tensile strength above 800 MPa and a yield strength below 450 MPa. 
     
     
         15 . Strip of steel according to  claim 1 , wherein the steel in the thinner sections has a tensile strength above 980 MPa and a yield strength below 750 MPa. 
     
     
         16 . Strip of steel according to  claim 15 , wherein the steel in the thinner sections has a tensile strength above 980 MPa and a yield strength below 650 MPa. 
     
     
         17 . Tailor rolled blank produced from a strip of steel according to  claim 1 .