High-strength steel sheets with excellent formability and method for manufacturing the same

Abstract

Disclosed is a high-strength ferrite-martensite steel sheet with excellent formability comprising: 0.05-0.15 weight % of C; 0.15 weight % or less of Si; 0.5-2.7 weight % of Mn; 0.1-0.7 weight % of Al; 0.005-0.03 weight % of P; 0.01-0.3 weight % of Sb; 0.002-0.02 weight % of S; at least one element selected from the group consisting of 0.01-0.6 weight % of Mo and 0.0005-0.0035 weight % of B; and the balance Fe and incidental impurities.

1 . A high-strength ferrite-martensite steel sheet with excellent formability and superior contraction property, comprising: 0.05-0.15 weight % of C; 0.15 weight % or less of Si; 0.5-2.7 weight % of Mn; 0.1-0.7 weight % of Al; 0.005-0.03 weight % of P; 0.01-0.3 weight % of Sb; 0.002-0.02 weight % of S; at least one element selected from the group consisting of 0.01-0.6 weight % of Mo and 0.0005-0.0035 weight % of B; and the balance Fe and incidental impurities. 
     
     
         2 . The high-strength steel sheet as recited in  claim 1  further comprising: 0.15 weight % or less of at least one element selected from the group consisting of Ti, Nb and V in accordance with a target tensile strength. 
     
     
         3 . The high-strength steel sheet as recited in  claim 1 , wherein γ-Fiber orientation ((111)H/RD orientation) of the ferrite matrix is 0.35 volume % or more and cube orientation ((100)<001>) of the ferrite matrix is 0.2 volume % or less. 
     
     
         4 . A method for manufacturing a high-strength steel sheet with excellent formability and superior contraction property comprising the steps of:
 providing a slab comprising: 0.05-0.15 weight % of C; 0.15 weight % or less of Si; 0.5-2.7 weight % of Mn; 0.1-0.7 weight % of Al; 0.005-0.03 weight % of P; 0.01-0.3 weight % of Sb; 0.002-0.02 weight % of S; at least one element selected from the group consisting of 0.01-0.6 weight % of Mo and 0.0005-0.0035 weight % of B; and the balance Fe and incidental impurities, reheating the slab at 1,050-1,250° C.;   hot rolling the slab to adjust a reduction ratio at the last stand to be 10% or less;   winding the hot rolled steel sheet at 600-750° C. and then cold rolling the wound steel sheet; and   recrystallization-annealing the cold rolled steel sheet and then quenching the recrystallization-annealed steel sheet.   
     
     
         5 . The method as recited in  claim 4 , wherein the recrystallization annealing is performed at 750-850° C. for 30-180 seconds and the quenching is carried out at a rate of 15-2,000° C./s. 
     
     
         6 . The method as recited in  claim 4 , wherein 0.15 weight % or less of at least one element selected from the group consisting of Ti, Nb and V in accordance with a target tensile strength is added to provide a slap. 
     
     
         7 . A method for manufacturing a high-strength steel sheet of a dual phase structure that has excellent formability and superior contraction property even with one cycle of cold rolling and annealing process, comprising the step of adding an effective amount of Sb so as to suppress the development of cube orientation and rotated cube orientation ((100)<011>) and increase the development of (111)//RD orientation. 
     
     
         8 . The method as recited in  claim 7 , wherein the amount of Sb is 0.3 weight % or less. 
     
     
         9 . The method as recited in  claim 8 , wherein the amount of the amount of Sb is 0.01-0.3 weight %. 
     
     
         10 . A motor vehicle comprising the steel sheet of  claim 1 .