Process for producing a steel strip comprising a relatively high strength dual phase steel

Abstract

A relatively high strength dual phase steel for a cold-rolled or hot-rolled steel strip with excellent forming properties, in particular for lightweight vehicle construction, contains the elements (contents in mass-%): 0.1 to <0.16 of C, 0.02 to <0.05 of Al, 0.40 to <0.60 of Si, 1.5 to <2.0 of Mn, <0.020 of P, <0.003 of S, <0.01 of N, 0.01 of Nb, 0.02 of V, remainder iron including common incidental steel elements with optional addition of Ti. The demanded dual phase microstructure is produced during continuous annealing, wherein the cold-rolled or hot-rolled steel strip is heated in the continuous annealing furnace in a one-step process to a temperature in the range of 820 to 1000° C., preferably 840 to 1000° C., and the annealed steel strip is then cooled down from the annealing temperature with a rate of cooling between 15 and 30° C./s.

1 .- 8 . (canceled) 
   
   
       9 . A process for producing a cold-rolled or hot-rolled steel strip of a high strength dual phase steel having excellent forming property, comprising the steps of:
 selecting a cold-rolled or hot-rolled steel strip with a composition comprising, in mass-%,   
     0.1 to ≦0.16 of C, 
     0.02 to ≦0.05 of Al 
     0.40 to ≦0.60 of Si 
     1.5 to ≦2.0 of Mn 
     ≦0.020 of P 
     ≦0.003 of S 
     ≦0.01 of N 
     0.01 of Nb 
     0.02 of V, 
     remainder iron including common incidental steel elements;
 heating the steel strip in a continuous annealing furnace in a one-step process to an annealing temperature in the range of 820 to 1000° C.; and 
 cooling the annealed steel strip from the annealing temperature with a rate of cooling between 15 and 30° C./s. 
 
   
   
       10 . The process of  claim 9 , further comprising the step of adding Ti. 
   
   
       11 . The process of  claim 9 , wherein the steel strip is heated to a temperature of 840 to 1000° C. 
   
   
       12 . The process of  claim 9 , wherein the content of V is 0.06%. 
   
   
       13 . The process of  claim 9 , wherein the content of V is 0.08%. 
   
   
       14 . The process of  claim 9 , wherein the content of Nb is 0.02%. 
   
   
       15 . The process of  claim 9 , wherein the content of Nb is 0.04%. 
   
   
       16 . The process of  claim 10 , wherein the content of Ti is ≦0.01%. 
   
   
       17 . The process of  claim 9 , further comprising the step of refining the steel strip by hot dipping. 
   
   
       18 . The process of  claim 17 , further comprising the step of dressing the steel strip. 
   
   
       19 . The process of  claim 9 , wherein the cold-rolled or hot-rolled steel strip of dual phase steel is used for lightweight vehicle construction.