| 摘要 |
A high intensity cold-rolled steel sheet with excellent bending property and 750 MPa of yield strength and a manufacturing method for the same are disclosed. The manufacturing method for the high intensity cold-rolled steel sheet according to the present invention comprises a step of: 1) cold-rolling a steel sheet consisting of 0.05 to 0.1 weight % of carbon (C), 0.01 to 0.05 weight % of silicon (Si), 2.0 to 2.4 weight % of manganese (Mn), less than 0.05 weight % of phosphorus (P), less than 0.003 weight % of sulfur (S), 0.01 to 0.05 weight % of aluminum (Al), 0.1 to 0.5 weight % of boron (B), 0.002 to 0.006 weight % niobium (Nb), 0.01 to 0.03 weight % of titanium (Ti), less than 0.006 weight % of nitrogen (N), residual ferrum (Fe), and impurities; 2) annealing the cold-rolled steel sheet above the sub-critical point, A1; 3) firstly cooling the steel sheet to Martensite temperature; 4) over-aging the cooled steel sheet at the Martensite temperature; and 5) secondly cooling the over-aged steel sheet. [Reference numerals] (AA) START; (BB) END; (S110) Steel sheet cold-rolling; (S120) Annealing; (S130) Primary cooling; (S140) Over aging treatment; (S150) Secondary cooling |
