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1. (WO2015045951) STEEL FOR HIGH-STRENGTH BOLTS WHICH HAS EXCELLENT DELAYED FRACTURE RESISTANCE AND BOLT MOLDABILITY, AND BOLT

Pub. No.:    WO/2015/045951    International Application No.:    PCT/JP2014/074393
Publication Date: Fri Apr 03 01:59:59 CEST 2015 International Filing Date: Wed Sep 17 01:59:59 CEST 2014
IPC: C22C 38/00
C21D 1/18
C21D 9/00
C22C 38/50
F16B 35/00
Applicants: KABUSHIKI KAISHA KOBE SEIKO SHO(KOBE STEEL, LTD.)
株式会社神戸製鋼所
Inventors: MATSUMOTO, Yosuke
松本 洋介
INADA, Atsushi
稲田 淳
CHIBA, Masamichi
千葉 政道
URESHINO, Yoshimasa
嬉野 欣成
KATO, Reiko
加藤 令子
Title: STEEL FOR HIGH-STRENGTH BOLTS WHICH HAS EXCELLENT DELAYED FRACTURE RESISTANCE AND BOLT MOLDABILITY, AND BOLT
Abstract:
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.