| 摘要 |
PROBLEM TO BE SOLVED: To provide a thick steel plate which can enhance not only an average value of toughness in HAZ but also the minimum value even when high-heat input welding has been conducted and also has a superior uniformity of strength properties in the sheet thickness direction. SOLUTION: This thick steel plate satisfies a predetermined chemical component composition and includes oxides in which constituent elements except oxygen are, by mass%, 10%<Ti, 5%<Al<20% and 5%<Ca<40%. Among oxides, the oxides which have circle-equivalent diameters of less than 2 μm are 300 pieces/mm<SP>2</SP>or more, and the oxides which have circle-equivalent diameters of 2 μm or more are 100 pieces/mm<SP>2</SP>or less. When hardness in a t/4 position is defined as Hvq and hardness in a t/2 position is defined as Hvh, a value H determined by expression of (Hvq-Hvh)/Hvq is 0.07 or less. COPYRIGHT: (C)2011,JPO&INPIT
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