| 摘要 |
PROBLEM TO BE SOLVED: To provide low yield ratio high tensile strength steel which has excellent high temperature strength, and has satisfactory weldability and toughness, and to provide a production method therefor. SOLUTION: The high tensile strength steel comprises, by mass, 0.05 to 0.15% C, 0.1 to 0.6% Si, 0.8 to 2.0% Mn,≤0.02% P,≤0.01% S, 0.01 to 0.06% Nb, 0.7 to 1.2% Mo,≤0.06% Al and≤0.006% N, and has a weld cracking parameter P<SB>CM</SB>of≤0.25%, and the balance iron with inevitable impurities. The steel has a microstructure essentially consisting of polygonal or pseudo polygonal ferrite, and has no upper/lower yield points in a full thickness tensile test for steel. The steel, if required, comprises specified amounts of Ni, Cu, Cr, V, B, Ti, Mg, Ca and rare earth metals as well. As the production method therefor, after reheating at 1,000 to 1,250°C, the cumulative rolling draft at≤950°C is controlled to≥50%, and the rolling is finished at 700 to 800°C. Thereafter, air cooling is performed. COPYRIGHT: (C)2004,JPO
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