WELDED STEEL PIPE FOR LINEPIPE WITH HIGH COMPRESSIVE STRENGTH AND MANUFACTURING METHOD THEREOF

• US 20120285576A1
• Filed: 11/25/2010
• Published: 11/15/2012
• 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, Nishimura, Kimihiro, Tanizawa, Akihiko, Sueyoshi, Hitoshi, Horie, Masayuki, Kiyoto, Yasumitsu
• Granted Patent: US 9,089,919 B2
• Time in Patent Office: Days
• US Class Current: 138/177
• CPC Class Codes: B23K 9/0282 for welding tube sections
• CPC Class Codes: B23K 9/18 Submerged-arc welding
• CPC Class Codes: C21D 2211/002 Bainite
• CPC Class Codes: C21D 8/10 during manufacturing of tubular bodies
• CPC Class Codes: C21D 8/105 of ferrous alloys
• 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

Abstract

Provided are a steel pipe for a linepipe with high compressive strength and a heavy wall thickness, and a method of manufacturing the same. Lowering of yield stress caused by a Bauschinger effect can be suppressed by optimizing the metal microstructure of a steel plate without requiring particular forming conditions in forming the steel pipe, and without requiring heat treatment after pipe making. A steel pipe has the composition which contains by mass % 0.03 to 0.10% C, 0.30% or less Si, 1.00 to 2.00% Mn, 0.015% or less P, 0.003% or less S, 0.080% or less Al, 0.005 to 0.035% Nb, 0.005 to 0.020% Ti, and Fe and unavoidable impurities as a balance. The steel pipe has metal microstructure where a fraction of bainite is 60% or more, a fraction of rolled ferrite is 5% or less, and a fraction of M-A constituent (MA) is 3% or less.

Claims

1. A welded steel pipe for a linepipe having the composition which contains by mass % 0.03 to 0.10% C, 0.30% or less Si, 1.00 to 2.00% Mn, 0.015% or less P, 0.003% or less S, 0.080% or less Al, 0.005 to 0.035% Nb, 0.005 to 0.020% Ti, and Fe and unavoidable impurities as a balance, wherein

C(%)—

0.065Nb(%) is 0.025 or more, and

a Ceq value is 0.3 or more, and

the steel pipe has metal microstructure where an area fraction of bainite is 60% or more, an area fraction of rolled ferrite is 5% or less, an area fraction of M-A constituent (MA) is 3% or less, an average grain size of MA is 2 pm or less, and an aspect ratio of MA is 5 or less,

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 more kinds selected from a group consisting of 0.5% or less Cu, 1% 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. The welded steel pipe for a linepipe according to claim 1, wherein the composition further contains by mass % one or more kinds selected from a group consisting of 0.20 to 0.40% Cu, 0.05 to 1.00% Ni, 0.0005 to 0.0035% Ca, 0.50% or less Cr, 0.50% or less Mo and 0.10% or less V, and C(%)—

0.065Nb(%)—

0.025Mo(%)—

0.057V(%) is 0.025 or more.

5. A method of manufacturing a welded steel pipe for a linepipe according to claim 1, wherein a steel plate is heated to a temperature which falls within a range of 1000 to 1200°

C., is subjected to hot rolling where a rolling reduction rate in a non-recrystallization temperature range is set to 60% or more and a rolling completion temperature is Ar₃ or above 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 above until a steel plate surface temperature falls within a range of 250 to 550°

C. and, subsequently, is subjected to reheating 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. thus manufacturing a steel plate, the steel plate is formed into a steel pipe shape by cold forming, welding is applied to seams of the steel pipe, and the steel pipe is subjected to pipe expansion with an expansion rate of 0.4% to 1.2%.

4. A method of manufacturing a welded steel pipe for a linepipe according to, wherein a steel plate is heated to a temperature which falls within a range of 1000 to 1200°

C., is subjected to hot rolling where a rolling reduction rate in a non-recrystallization temperature range is set to 60% or more and a rolling completion temperature is Ar₃ or above 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 above until a steel plate surface temperature falls within a range of 350 to 550°

C. thus manufacturing a steel plate, the steel plate is formed into a steel pipe shape by cold forming, welding is applied to seams of the steel pipe, and the steel pipe is subjected to pipe expansion with an expansion rate of 0.4% to 1.2%.