| 摘要 |
PROBLEM TO BE SOLVED: To provide a high tensile strength thick steel plate having excellent fatigue crack propagation resistance and brittle crack propagation arrest properties, and to provide its production method. SOLUTION: A steel stock having a composition comprising, by mass, 0.03 to 0.3% C, 0.03 to 1.5% Si, 0.1 to 3.0% Mn,≤0.1% Al and≤0.01% N, and the balance Fe with inevitable impurities, and having a structure composed of a ferritic phase and a pearlitic phase with a mean grain diameter is heated to a temperature in the temperature range of (an Ac<SB>1</SB>transformation point+30°C) to (an Ac<SB>1</SB>transformation point+100°C), is thereafter subjected to low rolling reduction multipass rolling at a cumulative draft of≥80% and at a rolling finishing temperature of≥550°C, and is next subjected to accelerated cooling. In this way, a multiple phase structure composed of a ferritic phase with a mean grain diameter as the main phase, and comprising an elongated bainitic phase and/or martensitic phase as the second phase is formed, thus a thick steel plate having excellent strength, toughness, fatigue crack propagation resistance and brittle crack propagation arrest properties is obtained. COPYRIGHT: (C)2008,JPO&INPIT
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