| 摘要 |
PROBLEM TO BE SOLVED: To provide a 570 MPa class thick steel plate having less acoustic anisotropy and also having excellent weldability and base-material toughness at very low temperature and also to provide a manufacturing method therefor. SOLUTION: The thick steel plate is characterized in that it has a specific chemical composition,≥90 vol.% of steel structure is composed of bainite, bainite block size is≤15μm, the average aspect ratio of oldγ-grains is≤3.0 and the value of TA1 defined by TA1=[Mn]+[Cr] (where square brackets represent the respective contents (mass%) of the elements) ranges from 2.00 to 4.00. A manufacturing method therefor is characterized in that, when heating steel having the specific chemical composition to a temperature between the Ac<SB>3</SB>point and 1,300°C and rolling it, the rolling of≥70% of total rolling reduction is done in the recrystallization region. COPYRIGHT: (C)2007,JPO&INPIT
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