Abstract: Provided herein is a high-strength seamless steel pipe containing a particular chemical composition. The volume fraction of tempered martensite is 90% or more in terms of a volume fraction. The number of nitride inclusions with a particle diameter of 4 ?m or more is 50 or less per 100 mm2, the number of nitride inclusions with a particle diameter of less than 4 ?m is 500 or less per 100 mm2, the number of oxide inclusions with a particle diameter of 4 ?m or more is 40 or less per 100 mm2, and the number of oxide inclusions with a particle diameter of less than 4 ?m is 400 or less per 100 mm2 in a cross section perpendicular to a rolling direction.

Abstract: A low alloy high strength thick-walled seamless steel pipe for oil country tubular goods is provided having a wall thickness of 40 mm or more and a yield strength of 758 MPa or more, the steel pipe including a composition containing, in terms of mass %, C: 0.25 to 0.31%, Si: 0.01 to 0.35%, Mn: 0.55 to 0.70%, P: 0.010% or less, S: 0.001% or less, O: 0.0015% or less, Al: 0.015 to 0.040%, Cu: 0.02 to 0.09%, Cr: 0.8 to 1.5%, Mo: 0.9 to 1.6%, V: 0.04 to 0.10%, Nb: 0.005 to 0.05%, B: 0.0015 to 0.0030%, Ti: 0.005 to 0.020%, and N: 0.005% or less, and having Ti/N of 3.0 to 4.0, with the balance being Fe and inevitable impurities, wherein a cumulative frequency rate at a measurement point at which a Mo segregation degree by a predetermined expression is 1.5 or more is 1% or less.

Abstract: A low alloy high strength seamless steel pipe for oil country tubular goods is provided including a composition containing, in terms of mass %, C: 0.25 to 0.31%, Si: 0.01 to 0.35%, Mn: 0.45 to 0.70%, P: 0.010% or less, S: 0.001% or less, 0: 0.0015% or less, Al: 0.015 to 0.080%, Cu: 0.02 to 0.09%, Cr: 0.8 to 1.5%, Mo: 1.1 to 1.6%, V: 0.01 to 0.06%, Nb: 0.005 to 0.015%, B: 0.0015 to 0.0030%, Ti: 0.005 to 0.020%, and N: 0.005% or less, and having a ratio of the Ti content to the N content of 3.0 to 4.0, with the balance being Fe and inevitable impurities, the steel pipe having a ratio of a stress at a strain of 0.7% to a stress at a strain of 0.4% in a stress-strain curve of 1.02 or less and a yield strength of 861 MPa or more.

Abstract: The steel pipe of the present invention is a low alloy high strength seamless steel pipe for oil country tubular goods including a composition containing, in terms of mass %, C: 0.23 to 0.27%, Si: 0.01 to 0.35%, Mn: 0.45 to 0.70%, P: 0.010% or less, S: 0.001% or less, O: 0.0015% or less, Al: 0.015 to 0.080%, Cu: 0.02 to 0.09%, Cr: 0.8 to 1.5%, Mo: 0.5 to 1.0%, Nb: 0.02 to 0.05%, B: 0.0015 to 0.0030%, Ti: 0.005 to 0.020%, and N: 0.005% or less, and having a value of a ratio of the Ti content to the N content (Ti/N) of 3.0 to 4.0, with the balance being Fe and inevitable impurities, the steel pipe having a ratio of a stress at a strain of 0.7% to a stress at a strain of 0.4% in a stress-strain curve; of 1.02 or less and a yield strength of 655 MPa or more.

Abstract: The high-strength seamless steel pipe has a volume fraction of tempered martensite of 95% or more, and a prior austenite size number of 8.5 or more, and contains nitride inclusions having a size of 4 ?m or more and whose number is 100 or less per 100 mm2, nitride inclusions having a size of less than 4 ?m and whose number is 700 or less per 100 mm2, oxide inclusions having a size of 4 ?m or more and whose number is 60 or less per 100 mm2, and oxide inclusions having a size of less than 4 ?m and whose number is 500 or less per 100 mm2, in a cross section perpendicular to a rolling direction.

Abstract: A seamless steel pipe having a specific chemical composition. A ratio of Ti to N is in a range of 2.0 to 5.0. The steel pipe has a microstructure including tempered martensite having a volume ratio of 95% or more, and prior austenite grains having a grain size number of 8.5 or more. In a cross-section perpendicular to a rolling direction of the steel pipe a number of nitride-based inclusions having a particle size of 4 um or more is 100 or less per 100 mm2, a number of nitride-based inclusions having a particle size of less than 4 ?m is 1000 or less per 100 mm2, a number of oxide-based inclusions having a particle size of 4 ?m or more is 40 or less per 100 mm2, and a number of oxide-based inclusions having a particle size of less than 4 ?m is 400 or less per 100 mm2.

Abstract: A round bar tensile test specimen for a sulfide stress corrosion cracking test of a steel, the specimen including a parallel section, a shoulder section, and a grip section. A sectional shape of the shoulder section being formed by a curve having two or more radii of curvature. A radius of curvature R1 (mm) of a portion of the curve adjacent to the parallel section being 15 mm or more, and the radius of curvature R1 (mm) satisfying (0.22??119)?R1?100 in terms of load stress ? (MPa) of the sulfide stress corrosion cracking test. A length X1 (mm) of the portion of the curve having the radius of curvature R1 in a longitudinal direction of the test specimen satisfying X1??{(r/8)×(R1?r2/4)}. Additionally, other radii of curvature of the curve being smaller than the radius of curvature R1.

Abstract: A steel composition and method from making a dual phase steel therefrom. The dual phase steel may have carbon of about 0.05% by weight to about 0.12 wt %; niobium of about 0.005 wt % to about 0.03 wt %; titanium of about 0.005 wt % to about 0.02 wt %; nitrogen of about 0.001 wt % to about 0.01 wt %; silicon of about 0.01 wt % to about 0.5 wt %; manganese of about 0.5 wt % to about 2.0 wt %; and a total of molybdenum, chromium, vanadium and copper less than about 0.15 wt %. The steel may have a first phase consisting of ferrite and a second phase having one or more of carbide, pearlite, martensite, lower bainite, granular bainite, upper bainite, and degenerate upper bainite. A solute carbon content in the first phase may be about 0.01 wt % or less.

Abstract: A high-strength seamless steel pipe for oil country tubular goods comprising, by mass %, C: 0.20% to 0.50%, Si: 0.05% to 0.40%, Mn: more than 0.6% to 1.5% or less, P: 0.015% or less, S: 0.005% or less, Al: 0.005% to 0.1%, N: 0.006% or less, Mo: more than 1.0% to 3.0% or less, V: 0.05% to 0.3%, Nb: 0.001% to 0.020%, B: 0.0003% to 0.0030%, O: 0.0030% or less, and Ti: 0.003% to 0.025%, and wherein Ti/N: 2.0 to 5.0 is satisfied, a volume fraction of a tempered martensitic is 95% or more, prior austenite grains have a grain size number of 8.

Abstract: A high-strength seamless steel pipe for oil country tubular goods comprising, by mass %, C: 0.20% to 0.50%, Si: 0.05% to 0.40%, Mn: 0.3% to 0.9%, P: 0.015% or less, S: 0.005% or less, Al: 0.005% to 0.1%, N: 0.006% or less, Mo: more than 1.0% to 3.0% or less, V: 0.01% to less than 0.05%, Nb: 0.001% to less than 0.01%, B: 0.0003% to 0.0030%, O: 0.0030% or less, and Ti: 0.003% to 0.025%, and wherein Ti/N: 2.0 to 5.0 is satisfied, a volume fraction of a tempered martensitic is 95% or more, prior austenite grains have a grain size number of 8.

Abstract: Provided is a high-strength seamless steel pipe having the composition which contains, by mass %, 0.20 to 0.50% C, 0.05 to 0.40% Si, 0.3 to 0.9% Mn, 0.015% or less P, 0.005% or less S, 0.005 to 0.1% Al, 0.008% or less N, more than 0.6% and 1.7% or less Cr, more than 1.0% and 3.0% or less Mo, 0.01 to 0.30% V, 0.001% or more and less than 0.01% Nb, 0.0003 to 0.0030% B, and 0.0030% or less O (oxygen). The high-strength seamless steel pipe has the microstructure where a volume fraction of a tempered martensitic phase is 95% or more, and prior austenitic grains have a grain size number of 8.5 or more, and a segregation degree index Ps which is defined by a formula Ps=8.1 (XSi+XMn+XMo)+1.2XP is set to less than 65.

Abstract: Provided is a high-strength seamless steel pipe having the composition which contains, by mass %, 0.20 to 0.50% C, 0.05 to 0.40% Si, 0.3 to 0.9% Mn, 0.015% or less P, 0.005% or less S, 0.005 to 0.1% Al, 0.008% or less N, 0.6 to 1.7% Cr, 0.4 to 1.0% Mo, 0.01 to 0.30% V, 0.01 to 0.06% Nb, 0.0003 to 0.0030% B, and 0.0030% or less O (oxygen). The high-strength seamless steel pipe has the microstructure where a volume fraction of a tempered martensitic phase is 95% or more, and prior austenitic grains have a grain size number of 8.5 or more, and a segregation degree index Ps which is defined by a formula Ps=8.1 (XSi+XMn+XMo)+1.2XP relating to XM which is a ratio between a segregated portion content and an average content is set to less than 65.

Abstract: A round bar tensile test specimen for a sulfide stress corrosion cracking test of a steel, the specimen including a parallel section, a shoulder section, and a grip section. A sectional shape of the shoulder section being formed by a curve having two or more radii of curvature. A radius of curvature R1 (mm) of a portion of the curve adjacent to the parallel section being 15 mm or more, and the radius of curvature R1 (mm) satisfying (0.22??119)?R1?100 in terms of load stress ? (MPa) of the sulfide stress corrosion cracking test. A length X1 (mm) of the portion of the curve having the radius of curvature R1 in a longitudinal direction of the test specimen satisfying X1??{(r/8)×(R1?r2/4)}. Additionally, other radii of curvature of the curve being smaller than the radius of curvature R1.

Abstract: In an abrasion resistant welded steel pipe, each of a base material and a weld metal contains specific amounts of chemical composition. The base material of the abrasion resistant welded steel pipe has a Vickers hardness within the range of 150 to 250, and the weld metal has a Vickers hardness within the range of 230 to 350. A weld heat affected zone in the abrasion resistant welded steel pipe has a Vickers hardness within the range of 150 to 350. In the weld metal, the dispersion density of a sulfide having an aspect ratio of 5 or more and containing at least one selected from Fe, Mn, and Ti is 10 grains/mm2 or less. The abrasion resistant welded steel pipe that can be produced at high productivity and low cost with no reduction in weld crack resistance can be provided.

Abstract: A welded steel pipe with excellent welded heat-affected zone toughness includes a butt weld formed by prior welding either an inner surface or an outer surface with a single layer for each of the inner and outer surfaces, wherein in the metallographic structure of a welded heat-affected zone, the martensite-austenite constituent (MA) area fraction is 4% or less, the average prior-austenite grain size is 400 ?m or less, and the following items are taken into account: the average prior-austenite grain size of a welded heat-affected zone formed by prior welding, the average prior-austenite grain size of a welded heat-affected zone formed by subsequent welding, the bead width determined at a position 5 mm apart from the tip of a weld bead formed by subsequent welding, the fusion line tilt angle of a weld bead of prior welding, and the fusion line tilt angle of a weld bead of subsequent welding.

Abstract: An APIX100-grade high strength steel pipe includes a base material containing, in mass percentage, C: more than 0.03% and 0.08% or less, Si: 0.01% to 0.5%, Mn: 1.5% to 3.0%, P: 0.015% or less, S: 0.005% or less, Al: 0.01% to 0.08%, Nb: 0.005% to 0.025%, Ti: 0.005% to 0.025%, N: 0.001% to 0.010%, O: 0.005% or less, and B: 0.0003% to 0.0020%, further contains one or more of Cu, Ni, Cr, Mo, and V, satisfies 0.19?Pcm?0.25, the balance being Fe and unavoidable impurities, and has a TS of 760 to 930 MPa, a uniform elongation of 5% or more, and a YR of 85% or less; the seam weld metal has a specific composition.

Abstract: The present invention provides a high-strength steel plate having excellent resistance to cutting crack, excellent Charpy absorbed energy, excellent DWTT properties, a low yield ratio, and a tensile strength of 900 MPa or more, a method of producing the steel plate, and a high-strength steel pipe using the steel plate. As solving means, a steel plate contains, by % by mass, 0.03 to 0.12% of C, 0.01 to 0.5% of Si, 1.5 to 3% of Mn, 0.01 to 0.08% of Al, 0.01 to 0.08% of Nb, 0.005 to 0.025% of Ti, 0.001 to 0.01% of N, and at least one component of 0.01 to 2% of Cu, 0.01 to 3% of Ni, 0.01 to 1% of Cr, 0.01 to 1% of Mo, and 0.01 to 0.1% of V; wherein the contents of Ca, O, and S satisfy the equation below; the microstructure includes ferrite and a second hard phase, the area fraction of ferrite being 10 to 50%; cementite in the second phase has an average grin size of 0.5 ?m or less; and the total amount of Nb and the like contained in carbides thereof present in steel is 10% or less of the total content in steel.

Abstract: A steel composition and method from making a dual phase steel therefrom. The dual phase steel may have carbon of about 0.05% by weight to about 0.12 wt %; niobium of about 0.005 wt % to about 0.03 wt %; titanium of about 0.005 wt % to about 0.02 wt %; nitrogen of about 0.001 wt % to about 0.01 wt %; silicon of about 0.01 wt % to about 0.5 wt %; manganese of about 0.5 wt % to about 2.0 wt %; and a total of molybdenum, chromium, vanadium and copper less than about 0.15 wt %. The steel may have a first phase consisting of ferrite and a second phase having one or more of carbide, pearlite, martensite, lower bainite, granular bainite, upper bainite, and degenerate upper bainite. A solute carbon content in the first phase may be about 0.01 wt % or less.

Abstract: A high-strength steel pipe has a tensile strength of 800 MPa or more and includes a weld metal having high cold-cracking resistance and high low-temperature toughness, wherein the weld metal contains C: 0.04% to 0.09% by mass, Si: 0.32% to 0.50% by mass, Mn: 1.4% to 2.0% by mass, Cu: less than 0.5% by mass, Ni: more than 0.9% by mass but not more than 4.2% by mass, Mo: 0.4% to 1.5% by mass, Cr: less than 0.5% by mass, V: less than 0.2% by mass, and the remainder of Fe and incidental impurities, and CS values calculated from the weld metal components using the equation CS=5.1+1.4[Mo]?[Ni]?[Mn]?36.3[C] are equal to zero or more at both an internal surface and an external surface.

Abstract: An APIX100-grade high strength steel pipe includes a base material containing, in mass percentage, C: more than 0.03% and 0.08% or less, Si: 0.01% to 0.5%, Mn: 1.5% to 3.0%, P: 0.015% or less, S: 0.005% or less, Al: 0.01% to 0.08%, Nb: 0.005% to 0.025%, Ti: 0.005% to 0.025%, N: 0.001% to 0.010%, O: 0.005% or less, and B: 0.0003% to 0.0020%, further contains one or more of Cu, Ni, Cr, Mo, and V, satisfies 0.19?Pcm?0.25, the balance being Fe and unavoidable impurities, and has a TS of 760 to 930 MPa, a uniform elongation of 5% or more, and a YR of 85% or less; the seam weld metal has a specific composition.