| 摘要 |
PROBLEM TO BE SOLVED: To provide a high strength steel sheet of common steel or low alloy steel, which has excellent fatigue crack propagation resistance, and to provide a production method thereof. SOLUTION: A steel slab having a composition containing 0.02 to 0.5% C, 0.3 to 3.5% Mn,≤0.02% Al, 0.05 to 3.0% Mo and 0.0050 to 0.040% N, or further containing one or more kinds of metals selected from 0.2 to 2.5% Si, 0.02 to 0.15% P, 0.1 to 1.5% Cr and 0.001 to 0.010% rare earth metals is subjected to finish rolling at an Ar<SB>3</SB>point or higher, and is thereafter cooled at a cooling rate of≥30°C/s on the average till the subsequent coiling at 200 to 600°C. Alternatively, the hot rolled steel sheet having the composition is cold-rolled at a draft of≥30%, and is thereafter heated to a temperature in a ferrite-austenite two phase region where the ferrite fraction reaches≤10% or higher, and is held for≥30 sec. Next, the steel sheet is cooled to a temperature of 300 to 600°C with a cooling rate of≥10°C/s on the average, is held for≥5 sec, and is subsequently cooled. COPYRIGHT: (C)2004,JPO
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