High strength bolt excellent in delayed fracture resistance and method of production of same
2006
Advantageously prevented provide a high strength accompanied by problems as hydrogen embrittlement, in a delayed fracture phenomenon represented, and high strength bolt excellent in fracture resistance and a method for producing a delay, the high strength bolts by mass%, C: 0.2 ~ 0.6%, Si: 0.05 ~ 0.5%, Mn: 0.1% ~ 2%, Mo: 0.5 ~ 6%, Al: 0.005% ~ 0.5%, a tensile strength of 1400MPa or more, the screw bottom surface compressive residual stress 10 to 90% of the tensile strength. Further, from the bottom surface of the threaded portion to the original γ grains at least the surface layer of 50μm aspect ratio in the axial direction and radial direction of 2 or more, and hardness of the surface layer portion is Hv460 or more. After addition, in the manufacturing method, the steel having the above composition is shaped bolt head and a shaft portion, then heated to 900 ℃ ~ 1100 ℃ and quenching, tempering at a temperature of or above 580 ℃, then thread rolling rolling.
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