Sumitomo Metal Industries, Inc.

Nippon Steel Sumitomo Metal Corporation

Nobuyuki Hisamune

Kunio Kondo

Yuji Arai

Tomohiko Omura

Kenji Kobayashi

Hajime Osako

Nobutoshi Murao

A thick-walled seamless steel pipe for line pipe which has a high strength and improved toughness and corrosion resistance in spite of the thick wall and which is suitable for use as a riser and flow line has a chemical composition comprising, in mass percent, C: 0.02-0.08%, Si: at most 0.5%, Mn: 1.5-3.0%, Al: 0.001-0.10%, Mo: greater than 0.4%-1.2%, N: 0.002-0.015%, at least one of Ca and REM in a total amount of 0.0002-0.007%, and a remainder of Fe and impurities, with the impurities having the content of P: at most 0.05%, S: at most 0.005%, and O: at most 0.005%, the chemical composition satisfying the inequality: 0.8&#x2266;[Mn]&#xd7;[Mo]&#x2266;2.6, wherein [Mn] and [Mo] are the numbers equivalent to the contents of Mn and Mo, respectively, in mass percent.

Seamless steel pipe for line pipe and a process for its manufacture

A seamless steel pipe for line pipe having high strength and stable toughness and having resistance to sulfide corrosion cracking at low temperatures to room temperature is provided. A seamless steel pipe according to the present invention has a chemical composition comprising, in mass percent, C: 0.03-0.08%, Si: 0.05-0.5%, Mn: 1.0-3.0%, Mo: greater than 0.4% to 1.2%, Al: 0.005-0.100%, Ca: 0.001-0.005%, a remainder of Fe and impurities including N, P, S, O, and Cu, with the impurities containing at most 0.01% of N, at most 0.05% of P, at most 0.01% of S, at most 0.01% of O, and at most 0.1% of Cu, and having a microstructure comprising a bainitic-martensitic dual phase structure.

Method for manufacturing seamless steel pipe for line pipe

A seamless steel pipe for line pipe having a high strength and good toughness and corrosion resistance even though having a thick wall has a chemical composition comprising, in mass percent, C: 0.02-0.08%, Si: at most 0.5%, Mn: 1.5-3.0%, Al: 0.001-0.10%, Mo: greater than 0.4% to 1.2%, N: 0.002-0.015%, Ca: 0.0002-0.007%, and a remainder of Fe and impurities, wherein the contents of the impurities are at most 0.03% for P, at most 0.005% for S, at most 0.005% for O and less than 0.0005% for B and wherein the value of Pcm calculated by the following Equation (1) is at least 0.185 and at most 0.250. The steel pipe has a microstructure which primarily comprises bainite and which has a length of cementite of at most 20 micrometers:=[C]+[Si]/30+([Mn]+[Cr]+[Cu])/20+[Mo]/15+[V]/10+5[B]&#x2003;&#x2003;(1)

The present invention relates to the following seamless steel pipes excellent in strength, toughness and weldability, particularly suitable for submarine flow lines, and a manufacturing method thereof. An as-quenched seamless steel pipe having a chemical composition consisting of, by mass%, C: 0.03 to 0.08%, Mn: 0.3 to 2.5%, Al: 0.001 to 0.10%, Cr: 0.02 to 1.0%, Ni: 0.02 to 1.0%, Mo: 0.02 to 0.8%, Ti: 0.004 to 0.010%, N: 0.002 to 0.008%, Ca: 0.0005 to 0.005%, and the balance Fe and impurities, with not more than 0.25% of Si, not more than 0.05% of P, not more than 0.005% of S, less than 0.005% Nb, and less than 0.0003% of B as the impurities, and having a microstructure consisting of not more than 20 volume% of polygonal ferrite, not more than 10 volume% of a mixed microstructure of martensite and retained austenite, and balance bainite. B can be 0.0003 to 0.001%. Mg and/or REM can be contained. The manufacturing method is characterized by the cooling rate during quenching.

Seamless steel pipe and manufacturing method thereof

A high strength seamless steel pipe having mgh yield stress and excellent hydrogen-induced cracking resistance, comprises by mass %, C:-%, Si:-%, Mn:-%, p:% or less, S:% or less, Ti:-%, Al:-%, Cr:-%, Mo:-%, V:-%, Ca-%, N:% or less and O (Oxygen):% or less, the balance Fe and impurities. The steel microstructure is bainite and/or martensite and ferrite is precipitated at grain boundaries. The seamless steel pipe can contain at least one of Cu:-% and Ni:-%. To produce the pipe, it is desirable to limit a starting temperature of quenching after rolling, a cooling rate and a tempering temperature.

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Kinokawa, Japan

Nobuyuki Hisamune