HIGH TENSILE STRENGTH THICK STEEL PLATE HAVING EXCELLENT FATIGUE CRACK PROPAGATION RESISTANCE AND BRITTLE CRACK PROPAGATION ARREST PROPERTY AND ITS PRODUCTION METHOD

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 Ac₁ transformation point+30°C) to (an Ac₁ 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