Jfe Steel Corporation

Kyono Yasuda

Nobuyuki Ishikawa

Daisuke Mizuno

Ryuji Muraoka

Kazukuni Hase

Shigeru Endo

Tomoyuki Yokota

Haruo Nakamichi

Akihiko Tanizawa

Junji Shimamura

Hideyuki Kimura

Yutaka Matsui

Koji Fujimoto

Shusaku Ota

Shigeaki Sugimoto

A steel material for line pipes has a specific composition. The metallic microstructure of the steel material at a ⅛-plate thickness position below the surface 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. The 0.23% compressive strength of a portion of the steel material which extends from the surface to the ⅛-plate thickness position in a transverse direction is 340 MPa or more. The 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.

Steel material for line pipes, method for producing the same, line pipe, and method for producing the line pipe

A method for producing a steel material for line pipes including heating a steel having a specific composition to a temperature of 1000° C. to 1200° C.; performing hot rolling such that a cumulative rolling reduction ratio in a non-recrystallization temperature range is 60% or more, a cumulative rolling reduction ratio in a temperature range of (a rolling finish temperature +20° C.) or less is 50% or more, and a rolling finish temperature is the Artransformation point or more and 790° C. or less; subsequently performing accelerated cooling from a temperature of the Artransformation point or more, at a cooling rate of 10° C./s or more, to a cooling stop temperature of 200° C. to 450° C.; and then performing reheating such that the temperature of a surface of the steel plate is 350° C. to 550° C. and the temperature of the center of the steel plate is less than 550° C.

Steel material for line pipes, method for producing the same, and method for producing line pipe

A method for producing a steel material for line pipes which has a tensile strength of 570 MPa or more, a compressive strength of 440 MPa or more, and a thickness of 30 mm or more, the method including heating a steel having a specific composition to a temperature of 1000&#xb0; C. to 1200&#xb0; C.; performing hot rolling such that a cumulative rolling reduction ratio in a non-recrystallization temperature range is 60% or more, a cumulative rolling reduction ratio in a temperature range of (a rolling finish temperature +20&#xb0; C.) or less is 50% or more, and a rolling finish temperature is the Artransformation point or more and 790&#xb0; C. or less; and subsequently performing accelerated cooling from a cooling start temperature of the Artransformation point or more, at a cooling rate of 10&#xb0; C./s or more, until the temperature of a surface of a steel plate reaches 300&#xb0; C. to 500&#xb0; C.

There are proposed a method for measuring hydrogen-induced cracking which can measure hydrogen-induced cracking initiated in an interior of a test specimen during HIC test and a measuring apparatus used in this method. When cracks initiated in an interior of a test specimenimmersed in a test solutioncontaining hydrogen sulfide is measured by an ultrasonic probeplaced in a vessel, the position and size of cracks initiated in the interior of the test specimenare measured with the lapse of time at a state of immersing the test specimenin the test solution by scanning the ultrasonic probeor the test specimen

Method and apparatus for measuring hydrogen-induced cracking

A high-strength, high-toughness steel plate having excellent surface properties and a high absorbed energy includes, by mass %, C: 0.03% to 0.08%, Si: 0.01% to 0.50%, Mn: 1.5% to 2.5%, P: 0.001% to 0.010%, S: 0.0030% or less, Al: 0.01% to 0.08%, Nb: 0.010% to 0.080%, Ti: 0.005% to 0.025%, and N: 0.001% to 0.006%, and further includes at least one selected from Cu: 0.01% to 1.00%, Ni: 0.01% to 1.00%, Cr: 0.01% to 1.00%, Mo: 0.01% to 1.00%, V: 0.01% to 0.10%, and B: 0.0005% to 0.0030%, with the balance being Fe and unavoidable impurities. In a surface portion and a central portion in the thickness direction, the area fraction of Martensite-Austenite constituent is less than 3% and the area fraction of bainite is 90% or more, and in the central portion in the thickness direction, the average particle size of cementite in bainite is 0.5 &#x3bc;m or less.

High-strength, high-toughness steel plate and method for producing the same

A steel material for highly deformable line pipes that has superior strain aging resistance, superior HIC resistance, and a metallographic structure including ferrite, bainite, and martensite-austenite constituent. The area fraction of the martensite-austenite constituent is 0.5 to 5.0%, and the difference in hardness between the ferrite and the bainite is 60 or more in terms of Vickers hardness. Additionally, the steel material has a uniform elongation of 9% or more and a yield ratio of 90% or less both before a strain aging treatment at a temperature of 300&#xb0; C. or lower and after the strain aging treatment.

Steel material for highly deformable line pipes having superior strain aging resistance and superior HIC resistance, method for manufacturing same, and welded steel pipe

A steel material for highly deformable line pipes that has superior strain aging resistance, superior HIC resistance, and a metallographic structure composed mainly of ferrite and bainite. The total area fraction of the ferrite and the bainite is 90% or more, and the difference in hardness between the ferrite and the bainite is 70 or more in terms of Vickers hardness. Additionally, the steel material has a uniform elongation of 9% or more and a yield ratio of 90% or less both before a strain aging treatment at a temperature of 300&#xb0; C. or lower and after the strain aging treatment.

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Fukuyama, Japan

Kyono Yasuda