LOW YIELD RATIO HIGH-TENSILE STEEL PLATE EXCELLENT IN LOW-TEMPERATURE TOUGHNESS OF BASE METAL AND LOW-TEMPERATURE TOUGHNESS OF HAZ, AND METHOD FOR MANUFACTURING THE SAME

摘要

PROBLEM TO BE SOLVED: To provide a steel plate for multi-purpose tanks for loading various liquefied gas such as LPG and liquid ammonia (LAG) which has excellent strength, weldability, and low-temperature toughness, and to provide a method for manufacturing the same.;SOLUTION: The method comprises heating a steel slab, which contains, by mass%, 0.03-0.1% C, 0.05-0.2% Si, 1.6-2.0% Mn, 0.015% or less P, 0.015% or less S, 0.05-0.15% Mo, 0.008-0.02% Ti, 0.005-0.05% Nb, 0.005% or less Al, 0.004% or less N, and 0.001-0.004% O, to a temperature of 1,050°C or higher but 1,200°C or lower, then hot-rolling it with a cumulative rolling reduction of 30% or more in a non-recrystallizing temperature region of 850°C or lower, and completing the hot rolling at a temperature of 720°C or higher, followed by cooling it at a cooling rate of 5°C/s or higher from a temperature of 700°C or higher to a temperature of 100°C or higher but 200°C or lower.;COPYRIGHT: (C)2009,JPO&INPIT