| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for industrially and stably manufacturing a non-heat-treated high-tensile strength steel plate having superior toughness, a tensile strength of 690 MPa or higher and further superior weldability, even with a comparatively thick plate thickness (30 mm or thicker). SOLUTION: This steel has a composition containing extra low carbon, high Mn, and an appropriate amount of Cu, Nb and B. The manufacturing method comprises heating a steel slab having the above composition to 1,000-1,350°C; hot-rolling it under a condition of an accumulation rolling reduction of 20% or higher in the temperature range of 950°C or lower, and of a rolling finishing temperature of an Ar<SB>3</SB>point or higher but 950°C or lower; after finishing the rolling, starting an accelerated cooling in a cooling rate of 5°C/s or higher from a temperature higher than Ar<SB>3</SB>point; and stopping the accelerated cooling at 450°C or lower. COPYRIGHT: (C)2004,JPO
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