WELDED STEEL PIPE FOR LINEPIPE HAVING HIGH COMPRESSIVE STRENGTH AND EXCELLENT SOUR GAS RESISTANCE AND MANUFACTURING METHOD THEREOF

• US 20130000793A1
• Filed: 11/25/2010
• Published: 01/03/2013
• Est. Priority Date: 11/25/2009
• Status: Active Grant

• Current Assignee: JFE Steel Corporation (JFE Holdings Incorporated)
• Original Assignee: JFE Steel Corporation (JFE Holdings Incorporated)
• Inventors: Ishikawa, Nobuyuki, Tanizawa, Akihiko, Sueyoshi, Hitoshi, Horie, Masayuki, Kiyoto, Yasumitsu, Shikanai, Nobuo
• Granted Patent: US 9,181,609 B2
• Time in Patent Office: Days
• US Class Current: 148/521
• CPC Class Codes: B21C 37/08 Making tubes with welded or soldered seams with helically arranged seams B21C37/122
• CPC Class Codes: B21C 37/30 Finishing tubes, e.g. sizing, burnishing
• CPC Class Codes: C21D 1/20 Isothermal quenching, e.g. bainitic hardening
• CPC Class Codes: C21D 2211/002 Bainite
• CPC Class Codes: C21D 2211/008 Martensite
• CPC Class Codes: C21D 8/0226 Hot rolling
• CPC Class Codes: C21D 8/0263 following hot rolling
• CPC Class Codes: C21D 8/10 during manufacturing of tubular bodies
• CPC Class Codes: C21D 9/50 for welded joints
• CPC Class Codes: C22C 38/001 containing N
• CPC Class Codes: C22C 38/002 containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
• CPC Class Codes: C22C 38/02 containing silicon
• CPC Class Codes: C22C 38/04 containing manganese
• CPC Class Codes: C22C 38/06 containing aluminium
• CPC Class Codes: C22C 38/12 containing tungsten, tantalum, molybdenum, vanadium, or niobium
• CPC Class Codes: C22C 38/14 containing titanium or zirconium
• CPC Class Codes: C22C 38/44 with molybdenum or tungsten
• CPC Class Codes: C22C 38/46 with vanadium
• CPC Class Codes: C22C 38/48 with niobium or tantalum
• CPC Class Codes: C22C 38/50 with titanium or zirconium
• CPC Class Codes: F17D 1/16 : Facilitating the conveyance of liquids or effecting the conveyance of viscous products by modification of their viscosity changing the flow or the viscosity by adding a chemical agent C09K3/00, C10M

Abstract

Provided is a steel pipe for a linepipe having high compressive strength, a heavy wall thickness and sour gas resistance. The steel pipe has the composition which contains by mass % 0.02 to 0.06% C, 0.01 to 0.5% Si, 0.8 to 1.6% Mn, 0.012% or less P, 0.0015% or less S, 0.01 to 0.08% Al, 0.005 to 0.050% Nb, 0.005 to 0.025% Ti, 0.0005 to 0.0035% Ca, 0.0020 to 0.0060% N, and Fe and unavoidable impurities as a balance. The steel pipe has metal microstructure where a fraction of bainite is 80% or more, a fraction of M-A constituent is 2% or less and an average grain size of bainite is 5 μm or less.

Claims

1. A welded steel pipe for a linepipe having the composition which contains by mass % 0.02 to 0.06% C, 0.01 to 0.5% Si, 0.8 to 1.6% Mn, 0.012% or less P, 0.0015% or less S, 0.01 to 0.08% Al, 0.005 to 0.050% Nb, 0.005 to 0.025% Ti, 0.0005 to 0.0035% Ca, 0.0020 to 0.0060% N, and Fe and unavoidable impurities as a balance, wherein

C(%)-0.065Nb(%) is 0.025 or more,

a CP value is 0.95 or less,

a Ceq value is 0.28 or more,

Ti/N is a value which falls within a range of 1.5 to 4.0, and

the steel pipe has metal microstructure where a fraction of bainite is 80% or more, a fraction of M-A constituent (MA) is 2% or less, and an average grain size of bainite is 5 μ

m or less, wherein the CP value is expressed by the formula;

CP=4.46C(%)+2.37Mn(%)/6+{1.18Cr(%)+1.95Mo(%)+1.74V(%)}/5+{1.74Cu(%)+1.7Ni(%)}/15+22.36P(%); and

wherein the Ceq value is expressed by the formula;

Ceq=C(%)+Mn(%)/6+{Cr(%)+Mo(%)+V(%)}/5+{Cu(%)+Ni(%)}/15.

2. The welded steel pipe for a linepipe according to claim 1, wherein the composition further contains by mass % one or two kinds or more selected from a group consisting of 0.5% or less Cu, 1.0% or less Ni, 0.5% or less Cr, 0.5% or less Mo, and 0.1% or less V, and C(%)-0.065Nb(%)-0.025Mo(%)-0.057V(%) is 0.025 or more.

3. A method of manufacturing a welded steel pipe for a linepipe, wherein steel having the composition described in claim 1 is heated to a temperature which falls within a range of 950 to 1200°

C., is subjected to hot rolling where a rolling reduction rate in a no-recrystallization temperature range is set to 60% or more and a rolling completion temperature falls within a range of Ar₃ to (Ar₃+70°

C.), and subsequently, is subjected to accelerated cooling at a cooling rate of 10°

C./sec or more from a temperature of (Ar₃-30°

C.) or more to a temperature which falls within a range of 300°

C. or above to 550°

C. thus a steel plate being manufactured, the steel plate is formed into a steel pipe shape by cold forming, seam welding is applied to a butt portion of the steel pipe shape to form a steel pipe, and the steel pipe is subjected to pipe expansion with an expansion rate of 0.4 to 1.2%.

4. The method of manufacturing a welded steel pipe for a linepipe according to claim 3, wherein the steel plate is subjected to reheating following the accelerated cooling such that a steel plate surface temperature falls within a range of 550 to 720°

C., and a steel plate center temperature becomes below 550°

C.