| 摘要 |
PROBLEM TO BE SOLVED: To obtain weather resistant steel plate good in the toughness of the center part in the plate thickness by controlling the number of the defects in the specified steel plate width in the center part of the plate thickness in the steel plate to a specified value below and controlling the average grain diameter and maximum grain diameter in the austenitic crystal structure to the specified value or below. SOLUTION: This on-line type weather resistant thick steel plate is the one on which the number of the defects in the center part of the plate thickness in controlled to <100 pieces to 1 m of the steel plate width, also, the average grain diameter(d) in the austentic crystal structure satisfies the inequality I (in the inequality I, YS denotes the yield stress or 0.2% proof stress: N/mm2 of the steel plate), and the maximum grain diameter is controlled to <=100μm. Preferably, the steel components contain, by weight, 0.06 to 0.1% C, 0.15 to 0.55% Si, 0.5 to 1.4% Mn, 0.2 to 0.5% Cu, 0.05 to 0.3% Ni, 0.3 to 0.8% Cr, 0.01 to 0.1% Al and 0.001 to 0.006% N, and P cm value expressing weld crack sensitivity expressed by the formula II [in the formula II, (t) denotes the steel plate thickness: mm)] is <0.22. For preventing the increase of the hardness of the heat-affected zone, the content of B as impurities is controlled to <0.0003%.
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