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1. (WO2013161089) Cr-CONTAINING STEEL PIPE FOR LINEPIPE EXCELLENT IN INTERGRANULAR STRESS CORROSION CRACKING RESISTANCE OF WELDED HEAT AFFECTED ZONE

Pub. No.:    WO/2013/161089    International Application No.:    PCT/JP2012/061699
Publication Date: Fri Nov 01 00:59:59 CET 2013 International Filing Date: Fri Apr 27 01:59:59 CEST 2012
IPC: C22C 38/00
C22C 38/58
Applicants: JFE STEEL CORPORATION
JFEスチール株式会社
MIYATA, Yukio
宮田 由紀夫
KIMURA, Mitsuo
木村 光男
Inventors: MIYATA, Yukio
宮田 由紀夫
KIMURA, Mitsuo
木村 光男
Title: Cr-CONTAINING STEEL PIPE FOR LINEPIPE EXCELLENT IN INTERGRANULAR STRESS CORROSION CRACKING RESISTANCE OF WELDED HEAT AFFECTED ZONE
Abstract:
A Cr-containing steel pipe for a linepipe, exhibiting a high strength of X65 to X80 grade, excellent toughness and corrosion resistance and excellent resistance to sulfide stress corrosion cracking and ensuring excellent resistance of a welded heat affected zone to intergranular stress corrosion cracking. Specifically, this steel pipe has a composition which contains, in mass%, 0.001 to 0.015% of C, 0.05 to 0.50% of Si, 0.10 to 2.0% of Mn, 0.001 to 0.10% of Al, 13 to less than 15% of Cr, 2.0 to 5.0% of Ni, 1.5 to 3.5% of Mo, 0.001 to 0.20% of V, and up to 0.015% of N so as to satisfy the relationships: P1 = 11.5 to 13.3 and P2 = (0.5Cr+5.0) - P1 ≥ 0. When the steel pipe is subjected to a welding process which comprises heating to a ferrite single-phase temperature region of 1300°C or higher and then cooling, the resulting welded heat affected zone has a structure such that: martensite accounts for at least 50% of the prior ferrite grain boundary in terms of the ratio to the overall length of the grain boundary; and the formation of Cr carbide depleted zones is minimized. Therefore, the welded heat affected zone exhibits remarkably improved resistance to intergranular stress corrosion cracking. The present invention can dispense with post weld heat treatment and thus has an effect of remarkably shortening the construction period of a welded steel pipe structure.