Title:
STEEL FOR HIGH STRENGTH BOLTS HAVING EXCELLENT DELAYED FRACTURE RESISTANCE AND HIGH STRENGTH BOLT
Document Type and Number:
WIPO Patent Application WO/2015/146331
Kind Code:
A1
Abstract:
Provided are: steel for high strength bolts, which exhibits excellent delayed fracture resistance without addition of an expensive alloy element such as Mo or V even if the steel has a high strength, namely a tensile strength of 1,100 MPa or more; and a high strength bolt which is formed of this steel and has excellent delayed fracture resistance.
Steel for high strength bolts, which has excellent delayed fracture resistance and contains, in mass%, 0.20-0.35% of C, 0.3-1.0% of Si, more than 0% but 0.6% or less of Mn, more than 0% but 0.02% or less of P, more than 0% but 0.02% or less of S, 0.3-1.5% of Cr, 0.01-0.1% of Al, 0.05-0.1% of Ti, 0.0003-0.005% of B and more than 0% but 0.01% or less of N with the balance made up of iron and unavoidable impurities, while satisfying formula (1) and formula (2). This steel for high strength bolts has a mixed structure of ferrite and pearlite. In formula (1) and formula (2), [ ] denotes the content (mass%) of each element.
1/([C] × [Mn]) ≥ 5.5 (1)
[C] + [Si]/2 + [Mn]/2 + [Cr]/3 ≥ 0.82 (2)
Inventors:
SAKATA MASAYUKI
CHIBA MASAMICHI
MATSUMOTO YOSUKE
CHIBA MASAMICHI
MATSUMOTO YOSUKE
Application Number:
PCT/JP2015/053763
Publication Date:
October 01, 2015
Filing Date:
February 12, 2015
Export Citation:
Assignee:
KOBE STEEL LTD (JP)
International Classes:
C22C38/00; C22C38/32; F16B35/00
Foreign References:
| JP2012162798A | 2012-08-30 | |||
| JP2013082963A | 2013-05-09 | |||
| JP2012041587A | 2012-03-01 | |||
| JP2011001599A | 2011-01-06 | |||
| JP2014015664A | 2014-01-30 |
Attorney, Agent or Firm:
UEKI, Kyuichi et al. (JP)
Hisakazu Ueki (JP)
Hisakazu Ueki (JP)
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