| 摘要 |
A high strength cold rolled steel sheet with high yield ratio and excellent elongation and stretch-flange-formability has a chemical composition including, by mass%, C: 0.06 to 0.13%, Si: 1.2 to 2.3%, Mn: 0.6 to 1.6%, P: not more than 0.10%, S: not more than 0.010%, Al: 0.01 to 0.10% and N: not more than 0.010%, the balance comprising Fe and inevitable impurities. The steel sheet includes a microstructure containing not less than 90% in terms of volume fraction of ferrite with an average grain diameter of less than 20 µm and 1.0 to 10% in terms of volume fraction of pearlite with an average grain diameter of less than 5 µm. The ferrite has an average Vickers hardness of not less than 130. The steel sheet has a yield ratio of not less than 65% and a tensile strength of not less than 590 MPa. |
