Title:
HIGH-STRENGTH STEEL AND HIGH-STRENGTH BOLT WITH EXCELLENT RESISTANCE TO DELAYED FRACTURE, AND MANUFACTURING METHOD THEREFOR
Document Type and Number:
WIPO Patent Application WO/2011/111873
Kind Code:
A1
Abstract:
The disclosed steel contains, by mass, 0.10-0.55% carbon, 0.01-3% silicon, and 0.1-2% manganese. Said steel also contains one or more of the following: 0.05-1.5% chromium; 0.05-0.2% vanadium; 0.05-0.40% molybdenum; 0.001-0.05% niobium; 0.01-4% copper; 0.01-4% nickel; and 0.0001-0.005% boron. The remainder comprises iron and unavoidable impurities. The structure of the disclosed steel is primarily tempered martensite. Said steel, which is a high-strength steel that exhibits excellent resistance to delayed fracture, is characterized by the following being formed in a surface layer thereof: (a) a nitrided layer with a thickness of at least 200 μm from the surface of the steel and a nitrogen concentration by mass that is at least 0.02% higher than that of the steel and no greater than 12.0%; and (b) a low-carbon region, at a depth between 100 μm and 1000 μm from the surface of the steel, with a carbon concentration by mass that is at most 0.9 times that of the steel and no less than 0.05%.
Inventors:
HIRAKAMI DAISUKE (JP)
CHIDA TETSUSHI (JP)
TARUI TOSHIMI (JP)
CHIDA TETSUSHI (JP)
TARUI TOSHIMI (JP)
Application Number:
PCT/JP2011/056482
Publication Date:
September 15, 2011
Filing Date:
March 11, 2011
Export Citation:
Assignee:
NIPPON STEEL CORP (JP)
HIRAKAMI DAISUKE (JP)
CHIDA TETSUSHI (JP)
TARUI TOSHIMI (JP)
HIRAKAMI DAISUKE (JP)
CHIDA TETSUSHI (JP)
TARUI TOSHIMI (JP)
International Classes:
C22C38/00; C21D1/06; C21D1/76; C21D9/00; C21D9/52; C22C38/58; C23C8/26; C23C8/30
Foreign References:
| JP2009299181A | 2009-12-24 | |||
| JPH10141341A | 1998-05-26 | |||
| JPH10226817A | 1998-08-25 | |||
| JPH0644566B2 | 1994-06-08 | |||
| JPH03243744A | 1991-10-30 | |||
| JPH03243745A | 1991-10-30 | |||
| JP2000337332A | 2000-12-05 | |||
| JP2000337333A | 2000-12-05 | |||
| JP2000337334A | 2000-12-05 | |||
| JPH10251803A | 1998-09-22 | |||
| JP2009299180A | 2009-12-24 |
Other References:
See also references of EP 2546380A4
Attorney, Agent or Firm:
AOKI, Atsushi et al. (JP)
Aoki 篤 (JP)
Aoki 篤 (JP)
Download PDF:
Claims: