High-strength cold rolled steel sheet having excellent shear processability, and manufacturing method therefor

Abstract

Provided is a high-strength cold rolled steel sheet having high shear processability, including, by wt %, C: 0.05% to 0.10%, Si: 0.01% to 0.5%, Mn: 1.2% to 2.0%, Al: 0.01% to 0.1%, Cr: 0.005% to 0.3%, B: 0.0003% to 0.0010%, Mo: 0.005% to 0.2%, P: 0.001% to 0.05%, S: 0.001% to 0.01%, N: 0.001% to 0.01%, Nb: 0.005% to 0.08%, Ti: 0.005% to 0.13%, V: 0.005% to 0.2%, and a balance of Fe and inevitable impurities. The high-strength cold rolled steel sheet satisfies Formulas 1 and 2 below, and the high-strength cold rolled steel sheet includes at least one of carbides, nitrides, and carbonitrides. Formula 1: 2.0≤[Mn]+2.5[Mo]+1.5[Cr]+300[B]≤2.5, Formula 2: 0.2≤([Nb]/93+[Ti]/48+[V]/51)/([C]/12+[N]/14)≤0.5 (in Formulas 1 and 2, each element symbol refers to a weight percent (wt %) of a corresponding element).

1 . A high-strength cold rolled steel sheet having high shear processability, the high-strength cold rolled steel sheet comprising, by wt %, carbon (C): 0.05% to 0.10%, silicon (Si): 0.01% to 0.5%, manganese (Mn): 1.2% to 2.0%, aluminum (Al): 0.01% to 0.1%, chromium (Cr): 0.005% to 0.3%, boron (B): 0.0003% to 0.0010%, molybdenum (Mo): 0.005% to 0.2%, phosphorus (P): 0.001% to 0.05%, sulfur (S): 0.001% to 0.01%, nitrogen (N): 0.001% to 0.01%, niobium (Nb): 0.005% to 0.08%, titanium (Ti): 0.005% to 0.13%, vanadium (V): 0.005% to 0.2%, and a balance of iron (Fe) and inevitable impurities,
 wherein the high-strength cold rolled steel sheet satisfies Formulas 1 and 2 below, and   the high-strength cold rolled steel sheet comprises at least one of carbides, nitrides, and carbonitrides,
   2.0≤[Mn]+2.5[Mo]+1.5[Cr]+300[B]≤2.5  Formula 1:
 
   0.2≤([Nb]/93+[Ti]/48+[V]/51)/([C]/12+[N]/14)≤0.5  Formula 2:
 
   where each element symbol in Formulas 1 and 2 refers to a weight percent (wt %) of a corresponding element.   
     
     
         2 . The high-strength cold rolled steel sheet of  claim 1 , wherein the carbides, the nitrides, and the carbonitrides have an average size within a range of 10 nm to 50 nm. 
     
     
         3 . The high-strength cold rolled steel sheet of  claim 1 , wherein the high-strength cold rolled steel sheet has a tensile strength of 1200 MPa or greater and a hardness of 340 Hv or greater. 
     
     
         4 . The high-strength cold rolled steel sheet of  claim 1 , wherein a maximum length of cracks formed during a shearing process of the high-strength cold rolled steel sheet is 1 mm or less. 
     
     
         5 . The high-strength cold rolled steel sheet of  claim 1 , wherein a microstructure of the high-strength cold rolled steel sheet before a cold rolling process comprises ferrite in an area fraction of 90% or greater, fine pearlite in an amount of less than 5%, and bainite as an inevitable remainder. 
     
     
         6 . A method for manufacturing a high-strength cold rolled steel sheet having high shear processability, the method comprising:
 reheating a steel slab to a temperature of 1200° C. to 1350° C., the steel slab comprising, by wt %, carbon (C): 0.05% to 0.10%, silicon (Si): 0.01% to 0.5%, manganese (Mn): 1.2% to 2.0%, aluminum (Al): 0.01% to 0.1%, chromium (Cr): 0.005% to 0.3%, boron (B): 0.0003% to 0.0010%, molybdenum (Mo): 0.005% to 0.2%, phosphorus (P): 0.001% to 0.05%, sulfur (S): 0.001% to 0.01%, nitrogen (N): 0.001% to 0.01%, niobium (Nb): 0.005% to 0.08%, titanium (Ti): 0.005% to 0.13%, vanadium (V): 0.005% to 0.2%, and a balance of iron (Fe) and inevitable impurities, the steel slab satisfying Formulas 1 and 2 below;   hot rolling the heated steel slab within a temperature range of 850° C. to 1150° C. to form a hot rolled steel sheet;   after the hot rolling, cooling the hot rolled steel sheet to a temperature of 550° C. to 750° C. and coiling the cooled hot rolled steel sheet; and   after the coiling, pickling the hot rolled steel sheet and cold rolling the hot rolled steel sheet at a reduction ratio of 60% to 70%,
   2.0≤[Mn]+2.5[Mo]+1.5[Cr]+300[B]≤2.5  Formula 1:
 
   0.2≤([Nb]/93+[Ti]/48+[V]/51)/([C]/12+[N]/14)≤0.5  Formula 2:
 
   where each element symbol in Formulas 1 and 2 refers to a weight percent (wt %) of a corresponding element.   
     
     
         7 . The method of  claim 6 , wherein the steel slab is manufactured through a continuous casting process. 
     
     
         8 . The method of  claim 6 , wherein the cooling of the hot rolled steel sheet is performed at an average cooling rate of 10° C./sec to 70° C./sec. 
     
     
         9 . The method of  claim 6 , wherein the cold rolled steel sheet comprises at least one of carbides, nitrides, and carbonitrides, and the carbides, the nitrides, and the carbonitrides have an average size within a range of 10 nm to 50 nm. 
     
     
         10 . The method of  claim 6 , wherein the cold rolled steel sheet has a tensile strength of 1200 MPa or greater and a hardness of 340 Hv or greater.