| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a cold-rolled steel sheet having a tensile strength of ≥780 MPa with ductility and bending property. <P>SOLUTION: The steel sheet has a chemical composition composed of 0.05-2.0% C, 0.2-2.0% Si, 0.5-2.8% Mn, 0.005-0.15% P, ≥0.02% S, 0.005-1.5% Al and the balance Fe with impurities, and has 60-80 vol% volume fraction of ferrite phase and further has the ratio Hnm/Hnf of the nano-hardness (Hnm) of low-temperature transforming phase to the nano-hardness (Hnf) of the ferrite phase being ≥3.0. In another embodiment, the volume fraction of the ferrite phase is 20-50 vol%, and the ratio Hnm/Hnf of the nano-hardness (Hnm) of the low-temperature transforming phase to the nano-hardness (Hnf) of the ferrite phase may be 2.0 or less. <P>COPYRIGHT: (C)2013,JPO&INPIT |
