| 摘要 |
PROBLEM TO BE SOLVED: To efficiently manufacture a high-tensile-strength steel with high toughness and high ductility, which has an adequate strength as a steel for a weld structure, is superior in ductility characteristics and low-temperature toughness, and has a high level of safety. SOLUTION: This manufacturing method comprises heating a steel slab having an appropriate chemical composition and a carbon content, to an AC3 transformation temperature or higher but 1,300°C or lower, hot-rolling it so as to include rolling in an unrecrystallized region of austenite with accumulated rolling reduction of at least 30% in a range between 950°C and the Ar3 transformation temperature, then acceleratingly cooling it from the Ar3 transformation temperature or higher to a temperature in which the austenite fraction becomes 20-70%, at 3-100°C/s, stopping accelerated cooling, then keeping the steel temperature within the accelerated-cooling stopping temperature±100°C, for 10 s-100 s after the above stop of accelerated cooling,,6y performing a combination of one or more of heating, holding, and cooling at a cooling rate of 0.5°C/s or lower, then cooling it, and tempering it as needed, at a heating temperature of 500°C or higher but the AC1 transformation temperature or lower. COPYRIGHT: (C)2003,JPO
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