| 摘要 |
PROBLEM TO BE SOLVED: To provide a steel plate for hull, excellent in impact energy absorptivity and capable of minimizing the breakage of a hull at the time of collision of a ship such as tanker, and its production. SOLUTION: The steel plate, having >=8 mm plate thickness, has a composition which consists of, by weight, 0.05-0.17% C, 0.05-1.0% Si, 0.5-2.0% Mn, 0.02-2.0% Al and the balance Fe with inevitable impurities and further contains strengthening elements if necessary and in which the value of PCM represented by PCM=C+Si/30+Mn/20 is regulated to <=0.22. In this case, residualγ-phase in an amount of 1.0 to 20% by area ratio is contained in the regions from the surface and the rear surface of the steel plate to positions at a depth of at least >=1/8 of the plate thickness from the surface and the rear surface, respectively. This steel plate is produced by subjecting, directly or after heating, a cast slab to hot rolling, finishing finish rolling at Ar3 +100 deg.C to Ar3 -50 deg.C, cooling the resultant steel plate down to Ar1 +100 deg.C to Ar1 deg.C at <=2 deg.C/s cooling rate, further cooling the steel plate at >=10 deg.C/s cooling rate, and stopping cooling at 250 to 450 deg.C.
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