Hoherfester mehrphasenstahl mit ausgezeichneten umformeigenschaften high strength multi-phase steel having excellent forming properties

Abstract

The invention relates to a high strength multi-phase steel for a cold- or hot-rolled steel strip having excellent forming properties, in particular for light vehicle construction, comprising the elements (contents in mass %): C 0.060 to=0.115; Al 0.020 to=0.060; Si 0.100 to=0.500; Mn 1.300 to=2.500; P=0.025; S=0.0100; Cr 0.280 to=0.480; Mo<0.150; Ti=0.005 to=0.050; Nb=0.005 to=0.050; B=0.0005 to=0.0060; N=0.0100; the remainder being iron including the usual elements present in steel and which are not mentioned above.

What is claimed is: 
     
         1 .- 18 . (canceled) 
     
     
         19 . A high strength multiphase steel for a cold or hot-rolled steel strip with excellent forming properties, in particular for lightweight vehicle construction comprising in weight %: 
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                   C 
                   0.060 to ≦0.115 
                 
                     
                   Al 
                   0.020 to ≦0.060 
                 
                     
                   Si 
                   0.100 to ≦0.500 
                 
                     
                   Mn 
                   1.300 to ≦2.500 
                 
                     
                   P 
                   ≦0.025  
                 
                     
                   S 
                   ≦0.0100 
                 
                     
                   Cr 
                     0.280 to ≦0.480 
                 
                     
                   Mo 
                   ≦0.150  
                 
                     
                   Ti 
                   ≧0.005 to ≦0.050 
                 
                     
                   Nb 
                   ≧0.005 to ≦0.050 
                 
                     
                   B 
                   ≧0.0005 to ≦0.0060 
                 
                     
                   N 
                   ≦0.0100 
                 
                     
                     
                 
             
                
               
               
                
                
                
                
                
                
                
                
                
                
                
                
                
               
            
           
         
         Remainder iron including common steel tramp elements not mentioned above. 
       
     
     
         20 . The steel of  claim 19 , wherein the Mo content is ≦0.100%. 
     
     
         21 . The steel of  claim 19 , wherein the Mo content is ≦0.050%. 
     
     
         22 . The steel of  claim 19 , wherein the Nb content is ≦0.045%. 
     
     
         23 . The steel of  claim 19 , wherein the Nb content is ≦0.040%. 
     
     
         24 . The steel of  claim 19 , wherein the Ti content is ≦0.045%. 
     
     
         25 . The steel of  claim 19 , wherein the Ti content is ≦0.040%. 
     
     
         26 . The steel of  claim 19 , wherein the B content is ≦0.005%. 
     
     
         27 . The steel of  claim 19 , wherein the B content is ≦0.0040%. 
     
     
         28 . The steel of  claim 19 , wherein the N content is ≦0.0090%. 
     
     
         29 . The steel of  claim 19 , wherein the N content is ≦0.0070%. 
     
     
         30 . The steel of  claim 19 , with a total content of Ti, Nb and B of ≦0.106%. 
     
     
         31 . The steel of  claim 19 , with a total content of Ti, Nb, B and Mo of ≦0.256%. 
     
     
         32 . A method for producing a cold or hot rolled steel strip from the high strength multiphase steel of  claim 19 , comprising:
 heating the cold-rolled strip in a continuous annealing furnace to an annealing temperature in the range from 700 to 950° C.;   cooling the annealed steel strip to an intermediate temperature of from 200 to 250° C. at a cooling speed between 15 and 100° C./s; and   cooling the steel strip from the intermediate temperature to room temperature with a cooling speed of 2 to 30° C./s or with a cooling speed between 15 and 100° C./s, wherein for the cooling speed of 2 and 30 C/s the steel strip is cooled on air, wherein a multiphase microstructure is established in the steel strip by the annealing and cooling steps.   
     
     
         33 . The method of  claim 32 , further comprising after the heating step and prior to the cooling steps, hot dip coating the steel strip by inserting the steel strip into a melting bath. 
     
     
         34 . The method of  claim 32 , further comprising after cooling to the intermediate temperature,
 holding the steel strip at the intermediate temperature for 1 to 20 seconds;   reheating the steel strip to a temperature of 420 to 470° C.;   hot dip coating the steel strip by inserting the steel strip into a melting bath; and   cooling the steel strip to the intermediate temperature of 200 to 250° C. with a cooling speed between 15 and 100 ° C./s, wherein the cooling to room temperature is performed with the cooling speed of from 2 and 30° C./s.   
     
     
         35 . The method of  claim 32 , further comprising dressing the steel strip. 
     
     
         36 . The method of  claim 32 , further comprising straightening the steel strip by stretching and bending.