| 摘要 |
High strength, hot rolled steel plate providing high level of bore expandability and high level of ductility. Also, method of manufacturing same. In first aspect, steel plate comprises steel having, by mass, C:0.01-0.15%; Si:0.30-2.00%; Mn:0.50-3.00%; P<=0.03%; S<=0.005%; Ti:0.01-0.50%; and/or Ni:0.01-0.05%, with balance Fe and unavoidable impurities. In this steel, >=80% of all grains have ratio of minor axis to major axis of >=0.1. This steel plate has steel structure comprising >=80% ferrite and balance bainite. In second aspect, steel plate has above composition, and ferrite-bainite duplex steel structure in which proportion of ferrite having grain diameter <=2 mum is >=80%. In third aspect, steel plate has above composition. wherein contents of C, Si, Mn, Ti, and Nb satisfy requirement represented by formula: 115 <=(917-480[C %]+100[Si %]-100[Mn %])-(790x([Ti %]+[Nb %]/2)0.05)<=235. This steel plate has steel structure comprising >=80% ferrite and balance bainite.
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