Abstract: It is provided a hot-rolled steel sheet as the material of an electric resistance welded steel pipe or tube with high strength and excellent workability and toughness, which is suitable for a machine structural steel pipe or tube used as a part of an automobile, construction machinery, or industrial machinery. The hot-rolled steel sheet has a predetermined chemical composition and has a steel microstructure at the sheet thickness center with a volume fraction of bainite of 90% or more and the balance containing one or more of ferrite, pearlite, martensite, and austenite. The above steel microstructure at the sheet thickness center further has an average grain size of 10.0 ?m or less, a volume fraction of crystal grains with a grain size of 40.0 ?m or more, and a number density of Ti-based inclusions with a long diameter length of 5.0 ?m or more of 20 pieces/mm2 or less.

Abstract: Provided is an electric resistance welded steel pipe or tube that has high strength and excellent workability and toughness and is suitable as a machine structural steel pipe or tube used in parts of automobiles, construction machinery, and industrial machinery. An electric resistance welded steel pipe or tube comprises a predetermined chemical composition, wherein a steel microstructure at a wall thickness center of a base metal portion has a volume ratio of martensite of 90% or more, with a balance containing one or more selected from ferrite, bainite, pearlite, and austenite, an average crystal grain size of 10 ?m or less, and a volume ratio of prior austenite with a grain size of 50 ?m or more of 40% or less.

Abstract: A high-strength seamless stainless steel pipe for oil wells is provided. The steel pipe has a component composition, which contains, in mass %, C: 0.015% or less, Si: 0.05 to 0.50%, Mn: 0.04 to 1.80%, P: 0.030% or less, S: 0.005% or less, Cr: 11.0 to 14.0%, Ni: more than 2.0% and 5.0% or less, Mo: 0.5% or more and less than 1.8%, Al: 0.005 to 0.10%, V: 0.005 to 0.20%, Nb: 0.005 to 0.05%, N: less than 0.015%, and O: 0.010% or less, and in which certain components satisfy a predetermined relational formula, and the remainder is made up of Fe and unavoidable impurities, a sum of an amount of precipitated Nb and an amount of precipitated V is 0.002% or more, a yield strength is 758 MPa or more, vE?60 is 20 J or more, and a corrosion rate is 0.125 mm/y or less.

Abstract: An electric resistance welded steel pipe having excellent formability and torsional fatigue resistance and a method for manufacturing the same. The electric resistance welded steel pipe includes a seam region and a base metal region, the seam region having a range of ±10 degrees in a pipe circumferential direction with respect to an electric resistance welded seam formed in a pipe longitudinal direction, the base metal region being a region other than the seam region. The electric resistance welded steel pipe has an r-value in the pipe longitudinal direction of 1.0 or greater, H (mm) and W (mm) satisfy a specified formula, and Ts(MAX) (mm) and Tb(Ave) (mm) satisfy a specified formula.

Abstract: Provided are a high-strength stainless seamless steel pipe for oil wells and a method for producing the same. The steel pipe has a chemical composition containing, by mass, C: 0.002% to 0.05%, Si: 0.05% to 0.50%, Mn: 0.04% to 1.80%, P: 0.030% or less, S: 0.0020% or less, Cr: more than 14.0% and 17.0% or less, Ni: 4.0% to 8.0%, Mo: 1.5% to 3.0%, Al: 0.005% to 0.10%, V: 0.005% to 0.20%, N: 0.002% to 0.15%, Ti: 0.002% to 0.020%, and O: 0.006% or less, the Cr, Ni, Mo, Cu, C, Si, Mn, and N satisfying predetermined relational expressions. The microstructure of the steel pipe includes a martensite phase with an area fraction of 70% or more. The average Ti concentration in inclusions having a major-axis length of 2 ?m or more is 10% by mass or more. The steel pipe has a yield strength of 758 MPa or more.

Abstract: Provided are a hot-rolled steel sheet for an electric resistance welded steel pipe and a method for manufacturing the same, an electric resistance welded steel pipe and a method for manufacturing the same, a line pipe, and a building structure. The hot-rolled steel sheet has a chemical composition containing, by mass %, C: 0.030% or more and 0.20% or less, Si: 0.02% or more and 1.0% or less, Mn: 0.40% or more and 3.0% or less, P: 0.050% or less, S: 0.020% or less, N: 0.0070% or more and 0.10% or less, and Al: 0.005% or more and 0.080% or less, the balance being Fe and incidental impurities, in which N dissolved in steel is contained in an amount of 0.0010% or more and 0.090% or less, and letting a sheet thickness be t, a steel microstructure at a ½t position has an average grain size of 20.0 ?m or less.

Abstract: Provided are a high-strength hot rolled steel sheet and a high-strength electric resistance welded steel pipe and methods for producing the same. In the steel microstructure of the steel sheet at the thickness center of the steel sheet, the volume fractions of bainite and ferrite are specific values, the average grain size is 9.0 ?m or less, and the dislocation density is 1.0×1014 m?2 or more and 1.0×1015 m?2 or less. In the steel microstructure at a position 0.1 mm below the surface, the volume fractions of bainite and ferrite are specific values, the average grain size is 9.0 ?m or less, the dislocation density is 5.0×1014 m?2 or more and 1.0×1015 m?2 or less, and the maximum low angle grain boundary density is 1.4×106 m?1 or less. The thickness of the steel sheet is 15 mm or more.

Abstract: An electric resistance welded steel pipe includes a base metal zone and an electric resistance welded zone. The base metal zone has a chemical composition containing, by mass, predetermined amounts of C, Si, Mn, P, S, Al, N, Nb, V, and Ti, with the balance being Fe and incidental impurities. The steel microstructure of the wall-thickness center of the base metal zone includes ferrite and bainite such that the total volume fraction of the ferrite and the bainite in the steel microstructure is 70% or more, with the balance being one or more selected from pearlite, martensite, and austenite. The steel microstructure has an average grain size of 7.0 m or less and a dislocation density of 1.0×1014 to 6.0×1015 m?2. The residual stress generated in the inner and outer surfaces of the pipe in the axial direction is 150 MPa or less.

Abstract: A metal pipe having an outer diameter of 150 mm to 3,000 mm and a wall thickness of 2 mm to 50 mm, and a method for manufacturing the same. The method includes a pipe-end-portion expansion step of expanding pipe end portions that are located at both ends of a mother pipe and an internal pressure application step that is performed after the pipe-end-portion expansion step and in which the mother pipe is expanded by applying an internal pressure, p, to the entire interior of the mother pipe until the internal pressure, p (MPa), that corresponds to changes in an axial compression amount s (mm), the axial compression amount, s, representing an amount of compression in a pipe axial direction against pipe extreme ends which are the both ends of the mother pipe, becomes a preset maximum internal pressure pmax (MPa), and p and s satisfy a specified formula.

Abstract: An electric resistance welded steel pipe and a method for manufacturing the same are provided. The present invention relates to an electric resistance welded steel pipe including a base metal zone and a weld. In the electric resistance welded steel pipe, steel microstructures at a wall-thickness-wise middle of the base metal zone are steel microstructures in which a bcc phase is present in a volume fraction greater than or equal to 80%, an average grain size is less than or equal to 15.0 ?m, and an A value, defined by a predetermined equation, is 0.55 or greater and 0.85 or less; a yield ratio in a pipe axis direction is less than or equal to 90%; and a Charpy absorbed energy at ?40° C. of the base metal zone is greater than or equal to 100 J.

Abstract: An electric resistance welded steel pipe having excellent formability and torsional fatigue resistance and a method for manufacturing the same. The electric resistance welded steel pipe includes a seam region and a base metal region, the seam region having a range of ±10 degrees in a pipe circumferential direction with respect to an electric resistance welded seam formed in a pipe longitudinal direction, the base metal region being a region other than the seam region. The electric resistance welded steel pipe has an r-value in the pipe longitudinal direction of 1.0 or greater, H (mm) and W (mm) satisfy a specified formula, and Ts(MAX) (mm) and Tb(Ave) (mm) satisfy a specified formula.

Abstract: Provided are a hot-rolled steel sheet for an electric resistance welded steel pipe and a method for manufacturing the same, an electric resistance welded steel pipe and a method for manufacturing the same, a line pipe, and a building structure. The hot-rolled steel sheet has a chemical composition containing, by mass %, C: 0.030% or more and 0.20% or less, Si: 0.02% or more and 1.0% or less, Mn: 0.40% or more and 3.0% or less, P: 0.050% or less, S: 0.020% or less, N: 0.0070% or more and 0.10% or less, and Al: 0.005% or more and 0.080% or less, the balance being Fe and incidental impurities, in which N dissolved in steel is contained in an amount of 0.0010% or more and 0.090% or less, and letting a sheet thickness be t, a steel microstructure at a ½t position has an average grain size of 20.0 ?m or less.

Abstract: An electric resistance welded steel pipe includes a base metal zone and an electric resistance welded zone. The base metal zone has a predetermined chemical composition and a microstructure including, by volume, ferrite: more than 30%, and bainite: 10% or more. The total volume fraction of the ferrite and the bainite is 70% or more and 95% or less. The balance being one or two or more phases selected from pearlite, martensite, and austenite. Further, when regions surrounded by boundaries between adjacent crystals having a misorientation of 15° or more are defined as crystal grains, the average size of the crystal grains is less than 7.0 ?m, and the volume fraction of crystal grains having a size of 40.0 ?m or more is 30% or less. A compressive residual stress generated in the inner and outer surfaces of the steel pipe in the axial direction is 250 MPa or less.

Abstract: Provided is a clad welded pipe or tube that has improved pipe or tube mechanical properties by reducing the width of a weld without its function as a clad pipe or tube being impaired. A clad welded pipe or tube comprises: a first layer made of base metal; and a second layer placed on one surface of the first layer, and made of first cladding metal that is a material different from the base metal, wherein a pipe or tube circumferential length L1 of weld metal at a pipe or tube inner surface and a pipe or tube circumferential length L2 of the weld metal at a pipe or tube outer surface in a weld are each 0.0010 mm or more and 1.0 mm or less, and the base metal is not exposed at a first cladding metal-side surface of the clad welded pipe or tube in the weld.

Abstract: A metal pipe having an outer diameter of 150 mm to 3,000 mm and a wall thickness of 2 mm to 50 mm, and a method for manufacturing the same. The method includes a pipe-end-portion expansion step of expanding pipe end portions that are located at both ends of a mother pipe and an internal pressure application step that is performed after the pipe-end-portion expansion step and in which the mother pipe is expanded by applying an internal pressure, p, to the entire interior of the mother pipe until the internal pressure, p (MPa), that corresponds to changes in an axial compression amount s (mm), the axial compression amount, s, representing an amount of compression in a pipe axial direction against pipe extreme ends which are the both ends of the mother pipe, becomes a preset maximum internal pressure pmax (MPa), and p and s satisfy a specified formula.

Abstract: Provided is an electric resistance welded clad steel pipe or tube in which a region where solidification microstructure is formed, i.e. a region in a weld particularly having significant influence on properties, is reduced without impairing its function as a clad pipe or tube. An electric resistance welded clad steel pipe or tube comprises: a first layer made of carbon steel or low-alloy steel as base metal; and a second layer placed on one surface of the first layer, and made of stainless steel or a nickel-containing alloy as cladding metal, wherein the base metal is not exposed at a cladding metal-side surface of the electric resistance welded clad steel pipe or tube in a weld, and no solidification microstructure is contained in each of circular sections of 0.1 mm in radius respectively centered at specific three positions in a plane perpendicular to a pipe or tube longitudinal direction.

Abstract: An electric-resistance-welded stainless clad steel pipe or tube that is excellent in both the fracture property of the weld and the corrosion resistance of the pipe or tube inner surface as electric resistance welded without additional welding treatment such as weld overlaying after electric resistance welding is provided. An electric-resistance-welded stainless clad steel pipe or tube comprises: an outer layer of carbon steel or low-alloy steel; and an inner layer of austenitic stainless steel having a predetermined chemical composition, wherein a flatness value h/D in a 90° flattening test in accordance with JIS G 3445 is less than 0.3, and a pipe or tube inner surface has no crack in a sulfuric acid-copper sulfate corrosion test in accordance with ASTM A262-10, Practice E, where h is a flattening crack height (mm), and D is a pipe or tube outer diameter (mm).

Abstract: An electric-resistance-welded stainless clad steel pipe or tube that is excellent in both the fracture property of the weld and the corrosion resistance of the pipe or tube inner surface as electric resistance welded without additional welding treatment such as weld overlaying after electric resistance welding is provided. An electric-resistance-welded stainless clad steel pipe or tube comprises: an outer layer of carbon steel or low-alloy steel; and an inner layer of austenitic stainless steel having a predetermined chemical composition, wherein a flatness value h/D in a 90° flattening test in accordance with JIS G 3445 is less than 0.3, and a pipe or tube inner surface has no crack in a sulfuric acid-copper sulfate corrosion test in accordance with ASTM A262-10, Practice E, where h is a flattening crack height (mm), and D is a pipe or tube outer diameter (mm).

Abstract: An electric-resistance-welded stainless clad steel pipe or tube that is excellent in both the fracture property of the weld and the corrosion resistance of the pipe or tube inner surface as electric resistance welded without additional welding treatment such as weld overlaying after electric resistance welding is provided. An electric-resistance-welded stainless clad steel pipe or tube comprises: an outer layer of carbon steel or low-alloy steel; and an inner layer of austenitic stainless steel having a predetermined chemical composition, wherein a flatness value h/D in a 90° flattening test in accordance with JIS G 3445 is less than 0.3, and a pipe or tube inner surface has no crack in a sulfuric acid-copper sulfate corrosion test in accordance with ASTM A262-10, Practice E, where h is a flattening crack height (mm), and D is a pipe or tube outer diameter (mm).

Abstract: Provided is a method for producing a circumferential weld joint. With this method, when low-carbon martensitic stainless steel pipes used for pipelines for transportation of petroleum and natural gas are subjected to circumferential welding, the circumferential welding can be performed efficiently using a low-cost welding material having a composition similar to the composition of the low-carbon martensitic stainless steel pipes. Pipe ends of low-carbon martensitic stainless steel pipes containing prescribed components are butted against each other and subjected to multi-pass arc welding using a welding material containing prescribed components. In the first pass in the multi-pass arc welding, CMT welding is performed in which the welding material is moved back and forth against a molten pool to generate an arc intermittently. In the second and subsequent passes, one selected from GMA welding, GTA welding, and the CMT welding is performed.