A resistance welded steel pipe is provided. A hot-rolled steel sheet having a composition containing, in mass %, C: 0.025 to 0.168%, Si: 0.10 to 0.30%, Mn: 0.60 to 1.90%, and one or at least two selected from Ca, Nb, V, and Ti such that Pcm is 0.20 or less is subjected to continuous cold roll forming to obtain a pipe-shaped body. Tapered grooves are formed in the steel sheet such that the ratio of the tapered portions to the wall thickness of the steel sheet is 10 to 80%. Then end surfaces of the pipe-shaped body are butted against each other and subjected to electric resistance welding. Ultrasonic waves are transmitted toward the electric resistance weld surface such that a beam width is within the range of 0.1 to 4.0 mm, and the reflected waves are used for ultrasonic flaw detection using an ultrasonic flaw detector.

A high-strength thick-walled electric resistance welded steel pipe has excellent low-temperature toughness and excellent HIC resistance and a yield strength of 400 MPa or more. The steel has a chemical composition consisting of C: 0.025% to 0.084%, Si: 0.10% to 0.30%, Mn: 0.70% to 1.80%, controlled amounts of P, S, Al, N, and O, Nb: 0.001% to 0.065%, V: 0.001% to 0.065%, Ti: 0.001% to 0.033%, and Ca: 0.0001% to 0.0035% on a mass percent basis and the remainder being Fe and incidental impurities, and satisfies Pcm of 0.20 or less.

A high-strength thick-walled electric resistance welded steel pipe has excellent low-temperature toughness and excellent HIC resistance and a yield strength of 400 MPa or more. The steel has a chemical composition consisting of C: 0.025% to 0.084%, Si: 0.10% to 0.30%, Mn: 0.70% to 1.80%, controlled amounts of P, S, Al, N, and O, Nb: 0.001% to 0.065%, V: 0.001% to 0.065%, Ti: 0.001% to 0.033%, and Ca: 0.0001% to 0.0035% on a mass percent basis and the remainder being Fe and incidental impurities, and satisfies Pcm of 0.20 or less.

A chemical conversion-treated steel pipe has a chemical conversion treatment film on a plated layer on a steel sheet. The plated layer is configured from a zinc alloy comprising 0.05-60 mass % aluminum and 0.1-10.0 mass % magnesium. The chemical conversion treatment film contains a fluorine resin, a base resin, metal flakes and a chemical conversion treatment component. The base resin is one or more selected from a group consisting of polyurethane, polyester, acrylic resins, epoxy resins and polyolefin. The content of fluorine resin with respect to the total amount of fluorine resin and base resin is at least 3.0 mass % calculated as fluorine atoms. The content of the base resin with respect to 100 parts by mass of the fluorine resin is at least 10 parts by mass. The content of metal flakes in the chemical conversion treatment film is greater than 20 mass % up to and including 60 mass %.

A chemical conversion-treated steel pipe has a chemical conversion treatment film on a plated layer on a steel sheet. The plated layer is configured from a zinc alloy comprising 0.05-60 mass % aluminum and 0.1-10.0 mass % magnesium. The chemical conversion treatment film contains a fluorine resin, a base resin, metal flakes and a chemical conversion treatment component. The base resin is one or more selected from a group consisting of polyurethane, polyester, acrylic resins, epoxy resins and polyolefin. The content of fluorine resin with respect to the total amount of fluorine resin and base resin is at least 3.0 mass % calculated as fluorine atoms. The content of the base resin with respect to 100 parts by mass of the fluorine resin is at least 10 parts by mass. The content of metal flakes in the chemical conversion treatment film is greater than 20 mass % up to and including 60 mass %.

A steel strip for an electric-resistance-welded steel pipe or tube having a strength of X70 grade or more and excellent HIC resistance and SSC resistance is provided. A steel strip for an electric-resistance-welded steel pipe or tube has a chemical composition containing, in mass %: C: 0.02% to 0.06%; Si: 0.1% to 0.3%; Mn: 0.8% to 1.3%; P: 0.01% or less; S: 0.001% or less; V: 0.04% to 0.07%; Nb: 0.04% to 0.07%; Ti: 0.01% to 0.04%; Cu: 0.1% to 0.3%; Ni: 0.1% to 0.3%; Ca: 0.001% to 0.005%; Al: 0.01% to 0.07%; and N: 0.007% or less, with a balance being Fe and incidental impurities, contents of C, Nb, V, and Ti satisfying the following Expression (1)

[C]−12([Nb]/92.9+[V]/50.9+[Ti]/47.9)≦0.03%  (1),

wherein a ferrite area ratio is 90% or more.

A steel strip for an electric-resistance-welded steel pipe or tube having a strength of X70 grade or more and excellent HIC resistance and SSC resistance is provided. A steel strip for an electric-resistance-welded steel pipe or tube has a chemical composition containing, in mass %: C: 0.02% to 0.06%; Si: 0.1% to 0.3%; Mn: 0.8% to 1.3%; P: 0.01% or less; S: 0.001% or less; V: 0.04% to 0.07%; Nb: 0.04% to 0.07%; Ti: 0.01% to 0.04%; Cu: 0.1% to 0.3%; Ni: 0.1% to 0.3%; Ca: 0.001% to 0.005%; Al: 0.01% to 0.07%; and N: 0.007% or less, with a balance being Fe and incidental impurities, contents of C, Nb, V, and Ti satisfying the following Expression (1)

[C]−12([Nb]/92.9+[V]/50.9+[Ti]/47.9)≦0.03%  (1),

wherein a ferrite area ratio is 90% or more.

A structural assembly includes a first member defining a matrix material, and a second member defining a skin. The skin has a roughed surface of hooks or barbs. The second member is engaged to the first member to define a mechanically interlocked assembly. The assembly may include an open-cell matrix material in a glue-less connection. The assembly may include a chemical bond in addition to a mechanical bond. The assembly may include internal layers of pre-impregnated composite fiber and resin. The skin member may act as a jig for a green composite member. The skin member may be deformed in a press to present a non-planar surface for such other members as may be attached to it. Assemblies may be formed with mechanical interconnection in place of glue or adhesive connections. Assemblies may be formed to may light, thin-walled pipe, flasks, pressure vessels and so forth.

A structural assembly includes a first member defining a matrix material, and a second member defining a skin. The skin has a roughed surface of hooks or barbs. The second member is engaged to the first member to define a mechanically interlocked assembly. The assembly may include an open-cell matrix material in a glue-less connection. The assembly may include a chemical bond in addition to a mechanical bond. The assembly may include internal layers of pre-impregnated composite fiber and resin. The skin member may act as a jig for a green composite member. The skin member may be deformed in a press to present a non-planar surface for such other members as may be attached to it. Assemblies may be formed with mechanical interconnection in place of glue or adhesive connections. Assemblies may be formed to may light, thin-walled pipe, flasks, pressure vessels and so forth.

A clad material includes a core material, a first skin material covering one side of the core material, and a second skin material covering the other side of the core material. The clad material is brazed in a state in which the first and second skin materials overlap each other. The core material is made of an Al alloy containing Mn (0.6 to 1.5 mass %), Ti (0.05 to 0.25 mass %), Cu (less than 0.05 mass %), Zn (less than 0.05 mass %), Fe (0.2 mass % or less), and Si (0.45 mass % or less) (balance: Al and unavoidable impurities). The first skin material is made of an Al alloy containing Si (6.8 to 11.0 mass %) and Zn (0.05 mass % or less) (balance: Al and unavoidable impurities). The second skin material is made of an Al alloy containing Si (4.0 to 6.0 mass %) and Cu (0.5 to 1.0 mass %) (balance: Al and unavoidable impurities).