| 摘要 |
PROBLEM TO BE SOLVED: To provide a high strength hot rolled steel sheet which has excellent stretch-flanging properties and fatigue properties. SOLUTION: The hot rolled steel sheet has a composition containing, by mass, 0.03 to 0.10% C, 0.05 to 1.5% Si, 1.0 to 2.0% Mn,≤0.05% P,≤0.01% S, 0.0005 to 0.01% N, and≤0.004% Al, and further containing either or both of Ti and Nb so as to satisfy -0.05≤äTi+(48/93)×Nb-(48/12)×C-(48/14)⊗N-(48/32)×S}≤0.2, and further containing Ce and O (oxygen) in 0.0003 to 0.012% Ce, and 0.0003 to 0.01% O, also so as to satisfy Ce/O≥0.25, and, if required, containing 0.2 to 2.0% Cu, and 0.1 to 1.0% Ni, and the balance Fe with inevitable impurities. The steel sheet has a structure in which the area ratio of a bainitic-ferritic phase is≥80%. COPYRIGHT: (C)2003,JPO
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