| 摘要 |
PROBLEM TO BE SOLVED: To provide a fatigue crack propagation delayed steel suitable for a welded structure or the like strongly requiring structural safety, and to provide its manufacturing method. SOLUTION: The steel member having excellent suppression in the progression of fatigue cracks has a composition containing, by mass, 0.02 to 0.25% C, 0.01 to 0.50% Si, 0.5 to 2.0% Mn,≤0.1% P,≤0.05% S, and the balance substantially iron with inevitable impurities, and further comprising one or more kinds of specified components and has a microstructure composed of a hard phase and a soft phase, and in which the product between a structural fraction parameter by formula (1): VP and a difference in hardness between the hard phase/soft phase by formula (2) is≥50: formula (1) is VP=VFH/50 in the case of 0<VFH≤50 and is VP=(100-VFH)/50 in the case of 50<VFH<100; wherein, VFH: the area fraction [%] of the hard phase, andΔHv=HvH-HvS(2); wherein HvH: the average Vickers hardness of the hard phase; and HvS: the average Vickers hardness of the soft phase. COPYRIGHT: (C)2009,JPO&INPIT |
