| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for manufacturing a high strength bolt excellent in delayed fracture resistance with which a hydrogen enbrittlement represented by the delayed fracture having≥1600 MPa tensile strength, is favorably prevented. SOLUTION: A steel composed by mass% of 0.2-0.6% C, 0.05-0.5% Si, 0.1-2% Mn, 0.5-10% Mo, 0.005-0.5% Al and if necessary, prescribed quantities of V, Ti, Nb, Cr, Ni, Cu, B and the balance Fe with inevitable impurities, is rapidly heated to 600-750°C at≥5°C/sec temperature-raising speed from at least≥300°C of the surface temperature of the steel material after forming martensitic structure by quenching from≥900°C, and air-cooled or acceleration-cooled after holding the steel at the above heating temperature range for 0-20sec. COPYRIGHT: (C)2007,JPO&INPIT
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