| 摘要 |
PURPOSE: An ultra high strength cold rolled steel having excellent coatability and workability and a method for manufacturing thereof are provided to prevent from generating a crack in manufacturing a slab by maintaining dissolved oxygen among steel in enough low state and by improving moldability of a steel sheet by developing crystal texture. CONSTITUTION: An ultra high strength cold rolled steel having excellent coatability and workability comprises as weight% C: 0.12-0.25%, Si: 0.4-0.6%, Mn: 2.0-2.5%, Al: 0.7-1.3%, Cu: 0.1-0.3%, Ni: 0.1-0.3%, P: less than 0.015% (0 is exclusion), S: 0.004 % (0 is exclusion), a remainder Fe, and other unavoidable impurities. A micro-structure comprises as an area fraction 45-65% of ferrite, 5-25% of a retained austenite, and 20-40% of bainite. The ultra high strength cold rolled steel comprises a Cu-based precipitate in which a mean size is 20-80nm. In the ultra high strength cold rolled steel, an inclusion in which a diameter per an original state is less than 2μm is distributed over 15/mm^2. |
