| 摘要 |
PROBLEM TO BE SOLVED: To provide a steel plate of 50 mm or more in the plate thickness and excellent in a brittle crack spreading-resistant characteristic in the plate thickness direction, suitable as a crack-arrester of a material to be welded (flange) of a ship-frame, such as a large container ship, a bulk-carrier, etc. SOLUTION: The steel plate is characterized in that a toughness in the plate thickness direction [Z-L or Z-T direction] is lower than the toughness in a rolling-direction [L-T direction] and the right angle direction to the rolling [T-L direction], and in the zone of≥1% in the plate thickness, this steel plate has a prescribed micro-structure and further, the average crystal grain diameter in the long-axial direction of the ferrite is≥5μm and the aspect ratio is≥2, or the average crystal grain diameter in the long-axial direction of the original austenite grain is≥10μm and the aspect ratio is≥2. Further, in the zone of≥10 mm in the thickness in the plate thickness direction, to the energy transition temperature obtained from the surface 2 mm V-notch Charpy impact test, the energy transition temperature in the plate thickness penetrating direction is made higher than 20°C. COPYRIGHT: (C)2008,JPO&INPIT
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