HIGH-STRENGTH HOT-ROLLED STEEL PLATE FOR LINE PIPES EXCELLENT IN LOW-TEMPERATURE TOUGHNESS AND PROCESS FOR PRODUCTION OF THE SAME

WIPO Patent Application WO/2008/132882

A1

The invention provides a high-strength hot-rolled steel plate for line pipes which is excellent in low-temperature toughness and a process for the production of the same. A steel plate which contains by mass C: 0.01 to 0.1%, Si: 0.05 to 0.5%, Mn: 1 to 2%, P: 0.03% or below, S: 0.005% or below, O: 0.003% or below, Al: 0.005 to 0.05%, N: 0.0015 to 0.006%, Nb: 0.005 to 0.08%, and Ti: 0.005 to 0.02% with the proviso that relationships: N-14/48xTi>0% et Nb-93/14x(N-14/48xTi)>0.005% are satisfied and with the balance consisting of Fe and unavoidable impurities, characterized in that the microstructure is a continuous cooling transformation structure, that the reflected X-ray intensity ratio between {211} plane and {111} plane which are parallel to the plate face, {211}/{111} ratio, in the texture in the thicknesswise central part of the plate is 1.1 or above, and that the density of carbonitride precipitate of Nb and/or Ti in the grains is 1017 to 1018 pieces/cm3.

YOKOI TATSUO (JP)
MINAGAWA MASANORI (JP)
HARA TAKUYA (JP)
YOSHIDA OSAMU (JP)
ABE HIROSHI (JP)

PCT/JP2008/054104

November 06, 2008

February 29, 2008

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NIPPON STEEL CORP (JP)
YOKOI TATSUO (JP)
MINAGAWA MASANORI (JP)
HARA TAKUYA (JP)
YOSHIDA OSAMU (JP)
ABE HIROSHI (JP)

C22C38/00; B21B1/26; B21B3/00; C21D8/02; C22C38/14; C22C38/58

JP2006274338A	2006-10-12
JP2005240051A	2005-09-08
JPH07173536A	1995-07-11
JPH11302776A	1999-11-02
JP2005264217A	2005-09-29
JP3846729B2	2006-11-15
JP2005503483A	2005-02-03
JPH0885841A	1996-04-02

See also references of EP 2116624A4
NIPPON STEEL MONTHLY, no. 380, 2004, pages 70

AOKI, Atsushi et al. (Toranomon 37 Mori Bldg.5-1, Toranomon 3-chome,Minato-k, Tokyo 23, JP)

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