30-01-2020 дата публикации
Номер: US20200032931A1
The present invention relates to steel pipe excellent in toughness of the weld metal part at a low temperature obtained by submerged arc welding in the longitudinal direction from both the inside and outside surfaces having strengths of the X60 to X70 class. The steel pipe of the present invention is a pipe having weld zones welded in a longitudinal direction at an inside surface and outside surface, wherein the tensile strength of the base metal is 480 to 620 MPa, the weld metal has a predetermined composition of constituents, when % X expresses a content of an element X in the weld metal, Pcm defined by Pcm=% C+% Si/30+(% Mn+% Cu+% Cr)/20+% Ni/60+% Mo/15+% V/10+5% B is 0.2% or less, Ceq defined by Ceq=% C+% Mn/6+(% Cr+% Mo+% V)/5+(% Ni+% Cu)/15 is 0.35 to 0.45%, α′ defined by α′=(1.5×(% O−0.89% Al)+3.4×% N−% Ti)×1000 is −20 to 40, and % Al/% O is 0.3 to 0.8. 1. A longitudinal seam welded steel pipe having weld zones welded at an inside surface and outside surface in a longitudinal direction ,a chemical composition of a base metal of the steel pipe containing, by mass %,C: 0.01 to 0.1%,Si: less than 0.5%,Mn: 0.5 to 2.0%,P: 0.015% or less,S: 0.01% or less,Al: 0.01 to 0.05%,Ti: 0.005 to 0.03%,N: 0.002 to 0.006%,O: 0.005% or less,Mg: 0 to 0.01%,Ca: 0 to 0.03%,Ni: 0 to 0.6%,Cr: 0 to 0.5%,Cu: 0 to 0.5%,Mo: 0 to 0.4%,Nb: 0 to 0.06%,B: 0 to 0.002%,V: 0 to 0.06% anda balance of Fe and impurities,a tensile strength of the base metal being 480 to 620 MPa,a chemical composition of a weld metal of the steel pipe containing, by mass %,C: 0.03 to 0.10%,Si: 0.03 to 0.50%,Mn: 0.5 to 2.0%,P: 0.015% or less,S: 0.010% or less,Al: 0.001 to 0.030%,Ti: 0.005 to 0.040%,N: 0.002 to 0.006%,B: 0 to 0.035%,O: 0.015 to 0.055%,Ni: 0 to 0.60%,Cr: 0 to 0.50%,Cu: 0 to 0.50%,Mo: 0 to 0.40%,V: 0 to 0.06%,Ca: 0 to 0.005%,Mg: 0 to 0.010%,Nb: 0 to 0.060% anda balance of Fe and impurities,wherein when % X expresses a content of an element X in the weld metal,Pcm defined by Pcm=% C+% Si/30+(% Mn+% Cu+% ...
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