| 摘要 |
<p>A hot-rolled steel sheet which comprises 0.01 to 0.2% by mass of C, 2.0% by mass or less of Si and 3.0% by mass or less of Mn and has a martensite phase as the main phase and a ferrite phase as a second phase, the ferrite phase containing ferrite having a grain size of 20 Vm or less in such an amount that the area ratio of ferrite becomes 1 to 30% (inclusive) and also containing 0.01% by mass or more of solid solution carbon. The steel sheet has excellent press workability, and exhibits excellent strain ageing property, that is, can be markedly increased in its tensile strength by a heat treatment, after press forming, at a temperature around that for a conventional baking finish, and thus can be suitably used as a steel sheet for an automobile. Further, fatigue characteristics after the strain ageing treatment are improved by hardening the ferrite phase.</p> |
