| 摘要 |
PROBLEM TO BE SOLVED: To provide steel which can be used for members on which repeated stress acts in vessels, marine structures, bridges, buildings, tanks or the like with no special post-treatment after cutting or welding and is excellent in fatigue characteristics of a cut portion or a welding HAZ portion, and to provide its production method. SOLUTION: The steel having excellent fatigue characteristics has a steel composition comprising 0.01 to 0.1% C, 0.01 to 0.6% Si, 0.4 to 2.0% Mn,≤0.02% P,≤0.01% S, 0.01 to 0.6% Cr, 0.005 to 0.06% Nb and/or 0.005 to 0.03% Ti,≤0.10% sol.Al and≤0.01% N, and the balance inevitable impurities, and regarding the diameter index DI and Mn/C prescribed by the expressions (1) and (2), DI is≥14 and Mn/C is≥15: (1), in the case of Mn<=1.2, DI=0.311×√C×(1+0.7×Si)×(1+3.33×Mn)×(1+2.16×Cr)×(1+3×Mo)×25.4, and (2), in the case of Mn>1.2, DI=0.311×√C×(1+0.7×Si)×(5+5.1×(Mn-1.2))×(1+2.16×Cr)×(1+3×Mo)×25.4. COPYRIGHT: (C)2005,JPO&NCIPI
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