| 摘要 |
<p>A high strength steel sheet, characterized in that it exhibits a metal structure comprising a ferrite phase and a hard second phase being dispersed in the ferrite phase, wherein the hard second phase accounts for 3 to 30 area % of the above metal structure, nano crystal grains having a grain diameter of 1.2 Vm or less account for 15 to 90 area % of the above ferrite phase and the average grain diameter (dS) of nano crystal grains having a grain diameter of 1.2 Vm or less and the average grain diameter (dL) of micro crystal grains having a grain diameter of more than 1.2 Vm satisfy the formula: (dL/dS >= 3). The above high strength steel sheet comprising nano crystal grains (having a grain diameter of 1.2 Vm or less) is suppressed in the content of alloying elements, exhibits an enhanced strength and also excellent balance of strength and ductility, which is important in press forming, and exhibits a difference of the stress in the dynamic deformation and the stress in the static deformation of 170 MPa or more, by containing finer ferrite crystal grains.</p> |
