| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a high strength thin steel sheet which has excellent elongation and press stability in retained austenite steel. <P>SOLUTION: The high strength steel sheet having excellent elongation and press forming stability has a steel composition comprising, by mass, 0.05 to 0.35% C, 0.05 to 2.0% Si, 0.8 to 3.0% Mn, 0.0010 to 0.1% P, 0.0005 to 0.05% S, 0.0010 to 0.010% N and 0.01 to 2.0% Al, and the balance iron with inevitable impurities, and has a microstructure composed of a ferrite phase and a bainite phase of 10 to 93% in total by area ratio, a retained austenite phase of 5 to 30% by area ratio and a martensite phase of 5 to 20% by area ratio, and in the steel sheet, the retained austenite phase has lath and insular form, and the area ratio γi of the insular retained austenite phase and the area ratio γof the whole retained austenite phase satisfy formula (1): 0.7≥γi/γ≥0.3. <P>COPYRIGHT: (C)2012,JPO&INPIT |
