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|1. (WO2015045951) STEEL FOR HIGH-STRENGTH BOLTS WHICH HAS EXCELLENT DELAYED FRACTURE RESISTANCE AND BOLT MOLDABILITY, AND BOLT|
|Applicants:||KABUSHIKI KAISHA KOBE SEIKO SHO(KOBE STEEL, LTD.)
|Title:||STEEL FOR HIGH-STRENGTH BOLTS WHICH HAS EXCELLENT DELAYED FRACTURE RESISTANCE AND BOLT MOLDABILITY, AND BOLT|
Provided is a steel for high-strength bolts, which can exhibit satisfactory delayed fracture resistance even under a severe condition and has good bolt moldability. The steel for high-strength bolts according to the present invention has a properly controlled chemical composition in which 0.10 to 0.30% of C and 0.4 to 0.7% of Ni are contained, and meets requirements respectively expressed by the formulae (1) and (2): (1) 0.85 ≤ [C]+[Si]/7+[Mn]/5+[Ni]/20+[Cr]/9+[Mo]/2 ≤ 1.3; and (2) [C]-(0.07×[Mo]+0.20×[V]) ≤ 0.20.