| 摘要 |
PROBLEM TO BE SOLVED: To provide a high strength bolt which has satisfactory hydrogen fatigue resistance and delayed fracture resistance, and tensile strength of≥1,600 MPa. SOLUTION: The bolt having excellent hydrogen embrittlement resistance comprises, by mass, 0.8 to 1.1% C, 0.05 to 2% Si, 0.2 to 2% Mn and 0.2 to 2% V, and the balance Fe with inevitable impurities, has a pearlite structure in which the aspect ratio of pearlite colonies is 1.3 to 4, and has tensile strength of≥1,600 MPa, and a delayed fracture limit diffusible hydrogen content of≥0.4 ppm and/or a fatigue limit diffusible hydrogen content of≥0.7 ppm. In its production method, steel is hot-rolled, thereafter cooled to the temperature range of 550 to 700°C at≥30°C/s, held to the temperature range for 30 to 300 s to control its tensile strength after pearlite transformation to≥1,350 MPa, subsequently subjected to wire drawing at a true strain in the range of 0.15 to 0.8, and cold-formed. COPYRIGHT: (C)2005,JPO&NCIPI
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