| 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: A steel containing C, Si, Mn, P, S, and the balance substantially iron with inevitable impurities, and further comprising one or two or more kinds of specified components as steel components is heated at 900 to 1,300°C, is subjected to rolling in which a cumulative draft at an Ar<SB>3</SB>point or above reaches≥50%, is cooled in the temperature range from an Ar<SB>3</SB>point or below to an Ar<SB>3</SB>-200°C or above at a cooling velocity of CRS[°C/s] in formula (3) or below for≥3 s, and is subsequently subjected to accelerated cooling to≤500°C at a cooling velocity of≥5°C/s: CRS[°C/s]=300/exp(5×CP+1)(3); wherein, CP=C+Mn/4+Cu/20+Ni/9+Cr/5+Mo/4. Also disclosed is a steel having the components and a microstructure composed of a hard phase and a soft phase, and in which the product between a specified structural fraction parameter: VP and a difference in hardness between the hard phase/soft phase:ΔHv by specified formula is≥50. COPYRIGHT: (C)2009,JPO&INPIT |
