| 摘要 |
<p>PURPOSE: A high-strength steel sheet with a low yield ratio and a method of manufacturing the steel sheet are provided to obtain a tensile strength of 980MPa or greater and a yield ratio of 0.55 or less after an annealing or galvanizing process by reducing the content of Nb while increasing the content of Cr relatively. CONSTITUTION: A method for manufacturing a high-strength steel sheet with a low yield ratio comprises the steps of: making hot rolled steel by reheating, hot rolling, cooling, and coiling steel slab, which comprises 0.06-0.2weight% of C, 0.05-0.3weight% of Si, 2.5-3.0weight% of Mn, 0.01-0.05weight% of P, 0.1-0.5weight% of Cr, 0.03-0.4weight% of Al, 0.01-0.04weight% of Nb, 0.005-0.2weight% of Ti, and the remaining amount of Fe and inevitable impurities(S110), pickling and cold rolling the hot rolled steel to obtain cold rolled steel(S120), and maintaining the cold rolled steel at 780-820°C and then cooling the steel to 550-250°C(S130), wherein the produced steel has a tensile strength of 980MPa or greater and a yield ratio of 0.55 or less. [Reference numerals] (AA) Start; (BB) End; (S110) Hot rolling step; (S120) Cold rolling step; (S130) Annealing step(Heat retention: 780-820°C, Cooling finish: 250-550°C)</p> |
