	US 12,227,814 B2
	Steel material for line pipes, method for producing the same, line pipe, and method for producing the line pipe
Kyono Yasuda, Tokyo (JP); Junji Shimamura, Tokyo (JP); and Ryuji Muraoka, Tokyo (JP)
Assigned to JFE Steel Corporation, Tokyo (JP)
Appl. No. 17/440,952
Filed by JFE Steel Corporation, Tokyo (JP)
PCT Filed Mar. 19, 2020, PCT No. PCT/JP2020/012169 § 371(c)(1), (2) Date Sep. 20, 2021, PCT Pub. No. WO2020/196214, PCT Pub. Date Oct. 1, 2020.
Claims priority of application No. 2019-062703 (JP), filed on Mar. 28, 2019.
Prior Publication US 2022/0220574 A1, Jul. 14, 2022
Int. Cl. C21D 9/08 (2006.01); B05D 7/14 (2006.01); C21D 6/00 (2006.01); C21D 8/10 (2006.01); C22C 38/00 (2006.01); C22C 38/02 (2006.01); C22C 38/06 (2006.01); C22C 38/24 (2006.01); C22C 38/42 (2006.01); C22C 38/44 (2006.01); C22C 38/48 (2006.01); C22C 38/50 (2006.01); C22C 38/58 (2006.01)

CPC C21D 9/085 (2013.01) [B05D 7/146 (2013.01); C21D 6/004 (2013.01); C21D 6/005 (2013.01); C21D 6/008 (2013.01); C21D 8/105 (2013.01); C22C 38/002 (2013.01); C22C 38/02 (2013.01); C22C 38/06 (2013.01); C22C 38/24 (2013.01); C22C 38/42 (2013.01); C22C 38/44 (2013.01); C22C 38/48 (2013.01); C22C 38/50 (2013.01); C22C 38/58 (2013.01)]

16 Claims

1. A steel material for line pipes, the steel material comprising a composition containing, by mass,

C: 0.030% to 0.10%,

Si: 0.01% to 0.15%,

Mn: 1.0% to 2.0%,

Nb: 0.005% to 0.050%,

Ti: 0.005% to 0.025%, and

Al: 0.08% or less,

the composition further containing one or more elements selected from, by mass,

Cu: 0.5% or less,

Ni: 1.0% or less,

Cr: 1.0% or less,

Mo: 0.5% or less, and

V: 0.1% or less, wherein a Ceq value represented by Formula (1) is 0.35 or more and a Pcm value represented by Formula (2) is 0.20 or less, with the balance being Fe and incidental impurities,

wherein a metallic microstructure of the steel material at a ⅛-plate thickness position relative to a surface of the steel material includes bainite of an area fraction of 85% or more, polygonal ferrite of an area fraction of 10% or less, and martensite-austenite constituent of an area fraction of 5% or less, and

wherein a 0.23% compressive strength of a portion of the steel material, the portion extending from the surface of the steel material to the ⅛-plate thickness position, in a rolling orthogonal direction is 340 MPa or more, and a temperature at which a percent ductile fracture of the steel material measured in a DWTT test becomes 85% or more is −10° C. or less,

Ceq value=C+Mn/6+(Cu+Ni)/15+(Cr+Mo+V)/5 (1)

Pcm value=C+Si/30+(Mn+Cu+Cr)/20+Ni/60+Mo/15+V/10 (2)

where, in Formulae (1) and (2), the symbol of each element represents the content (mass %) of the element and is zero when the steel material does not contain the element.