Jfe Steel Corporation

Shusaku Ota

Nobuyuki Ishikawa

Shigeru Endo

Kazukuni Hase

Hideyuki Kimura

Tomoyuki Yokota

Satoshi Ueoka

Junji Shimamura

Shigeki Kitsuya

Kyono Yasuda

Yuta Tamura

Shinichi Kakihara

Ryo Nagao

Yuya Sato

Yoshiaki Ota

Disclosed is, as a high-strength steel plate of API X80 grade or higher with a thickness of 38 mm or more, a thick steel plate for structural pipes or tubes that exhibits high strength in the rolling direction and excellent Charpy properties at its mid-thickness part without addition of large amounts of alloying elements. The thick steel plate for structural pipes or tubes disclosed herein has: a specific chemical composition; a microstructure at its mid-thickness part that is a dual-phase microstructure of ferrite and bainite with an area fraction of the ferrite being less than 50%, and that contains ferrite grains with a grain size of 15 &#x3bc;m or less in an area fraction of 80% or more with respect to the whole area of the ferrite; a tensile strength of 620 MPa or more; and a Charpy absorption energy vEat &#x2212;20&#xb0; C. at the mid-thickness part of 100 J or more.

Thick steel plate for structural pipes or tubes, method of producing thick steel plate for structural pipes or tubes, and structural pipes and tubes

Disclosed is, as a high-strength steel plate of API X80 grade or higher with a thickness of 38 mm or more, a steel plate for structural pipes or tubes that exhibits excellent resistance to PWHT and excellent toughness at the heat-affected zone, particularly at the butting faces joined by welding, without addition of large amounts of alloying elements. The steel plate for structural pipes or tubes disclosed herein has a specific chemical composition, in which the steel plate has mechanical properties including: (a) a 0.5% yield strength of 555 MPa or more; (b) a tensile strength of 625 MPa or more; and (c) a Charpy absorption energy vEat &#x2212;10&#xb0; C. at its mid-thickness part of 250 J or more, and maintains the mechanical properties (a) to (c) even after subjection to heat treatment at 650&#xb0; C. for 2 hours.

Steel plate for structural pipes or tubes, method of producing steel plate for structural pipes or tubes, and structural pipes and tubes

A high-strength steel having a specified chemical composition, wherein parameter Pis 0.050% or more, the relationship (TS&#x2212;TS)/TS&#x2264;0.050 is satisfied, wherein TS is defined as tensile strength determined at a temperature of 350&#xb0; C. after aging has been performed under the condition of a Larson-Miller Parameter (LMP) of 15700, and wherein TSis defined as tensile strength determined at a temperature of 350&#xb0; C. before the aging is performed, and having a toughness represented by a vEof 100 J or more in a weld heat-affected zone, which is formed when welding is performed.

High-strength steel, method for manufacturing high-strength steel, steel pipe, and method for manufacturing steel pipe

Disclosed is, as a high-strength steel plate of API X80 grade or higher with a thickness of 38 mm or more, a thick steel plate for structural pipes or tubes that exhibits high strength in the rolling direction, excellent Charpy properties at its mid-thickness part, and high material homogeneity without addition of large amounts of alloying elements. The thick steel plate for structural pipes or tubes disclosed herein has: a specific chemical composition; a microstructure mainly composed of bainite; a tensile strength of 620 MPa or more; a Charpy absorption energy vEat &#x2212;20&#xb0; C. at the mid-thickness part of 100 J or more; a variation of Vickers hardness in a plate thickness direction &#x394;HVof 50 or less; and a variation of Vickers hardness in a plate widthwise direction &#x394;HVof 50 or less.

High-strength steel having a specified chemical composition, wherein X (%) calculated by using equation (1):=0.35Cr+0.9Mo+12.5Nb+8V&#x2003;&#x2003;(1)is 0.75% or more, wherein the symbols of chemical elements in equation (1) respectively denote the contents (mass %) of the corresponding chemical elements and wherein the symbol of a chemical element which is not included is assigned a value of 0, a microstructure having a bainite phase fraction of 50% or more, a dislocation density of 1.0&#xd7;10/mor more after aging has been performed under the condition of a Larson-Miller parameter (LMP) of 15000, and a yield strength of 550 MPa or more before and after the aging is performed, as well as methods of manufacturing such high-strength steel, is disclosed. The high-strength steel can be used as a raw material for manufacturing large diameter steel pipe having the strength properties required for its use in steam transportation.

A high strength/highstrength, high toughness steel sheet having tensile strength, Charpy impact absorption energy, and ductile fracture rate are equal to or greater than specified values comprises, in mass %, 0.03-0.08% of C, 0.01-0.50% of Si, 1.5-2.5% of Mn, 0.001-0.010% of P, 0.0030% or less of S, 0.01-0.08% of Al, 0.010-0.080% of Nb, 0.005-0.025% of Ti, 0.001-0.006% of N, at least one substance selected from among 0.01-1.00% of Cu, 0.01-1.00% of Ni, 0.01-1.00% of Cr, 0.01-1.00% of Mo, 0.01-0.10% of V, and 0.0005-0.0030% of B, and a remainder of Fe and unavoidable impurities. At a position at &#xbd; the sheet thickness, the area ratio of island-like martensite is less than 3%, the area ratio of bainite is 90% or more, and the average particle size of cementite within the bainite is 0.5 &#x3bc;m or less.

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Tokyo, Japan

Shusaku Ota