| 摘要 |
<p>PURPOSE: A high-strength steel sheet with excellent workability and low-temperature brittleness and a manufacturing method thereof are provided to improve the ductility of a high-strength area having a tensile strength of 1180MPa or greater by increasing the volume ratio of ferrite. CONSTITUTION: A high-strength steel sheet comprises 0.10-0.30wt.% of C, 1.40-3.0wt.% of Si, 0.5-3.0wt.% of Mn, 0.1wt.% or less of P, 0.05wt.% or less of S, 0.005-0.20wt.% of Al, 0.01wt.% or less of N, 0.01wt.% or less of O, and the remaining amount of Fe and inevitable impurities. The microstructure of the steel sheet at 1/4 of thickness comprises 5-35 volume% of ferrite and 60 volume% of greater of bainitic ferrite and/or tempered martensite. When measured with an X-ray diffraction method, the microstructure includes residual austenite of 5 volume% or greater. The tensile strength of the steel sheet is 1180MPa or greater. [Reference numerals] (AA) Temperature; (BB) Ac3 point; (CC) 5°C/s or greater; (DD) Ac1 point + 20°C; (EE) 100 seconds or longer; (FF) Time</p> |
