An aspect of the present disclosure is to provide a method for manufacturing a welded structure capable of effectively suppressing welding LME cracks generated during spot welding of a zinc plated steel sheet having ultra-high strength, and a welded structure manufactured using the same.

Provided is a steel used for chassis parts, etc. of an automobile and, more specifically, to a hot rolled steel plate for an electric resistance welded steel pipe, which shows an excellent weldability in electric resistance welding, and a manufacturing method thereof.

A cold-rolled and heat-treated steel sheet having a microstructure consisting of, in surface fraction: between 10% and 30% of retained austenite, the retained austenite being present as films having an aspect ratio of at least 3 and as Martensite Austenite islands, less than 8% of the Martensite Austenite islands having a size above 0.5 μm, at most 1% of fresh martensite, at most 50% of tempered martensite, and recovered martensite containing precipitates of at least one element chosen among niobium, titanium and vanadium. A method for manufacturing the cold-rolled and heat-treated steel sheet is also described.

A cold-rolled and heat-treated steel sheet having a microstructure consisting of, in surface fraction: between 10% and 30% of retained austenite, the retained austenite being present as films having an aspect ratio of at least 3 and as Martensite Austenite islands, less than 8% of the Martensite Austenite islands having a size above 0.5 μm, at most 1% of fresh martensite, at most 50% of tempered martensite, and recovered martensite containing precipitates of at least one element chosen among niobium, titanium and vanadium. A method for manufacturing the cold-rolled and heat-treated steel sheet is also described.

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 μm or less.

Method for joining of at least two unweldable materials, non-weldable directly to each other with thermal joining processes in a lap joint configuration, where a two step sequence is used consisting of a first step to apply a thermomechanical or mechanical surface protection layer on the surface of an unweldable material and a second step, where a thermal joining process is used to joint the sprayed layer with an applied layer sheet.

A welding element is operable for being connected to a workpiece using a welding method. The welding element comprises: a head and a shaft like anchor portion. The head includes a welding surface, a stop surface that is remote from the welding surface, and a plurality of pointed projections evenly and uniformly distributed over the entire welding surface. The shaft-like anchor portion extends along a longitudinal axis between a first end region and a second end region, with the first end region connected to the stop surface.

A transition structure includes a metallic portion, a fiber portion including a plurality of tows embedded within the metallic portion and extending out from the metallic portion forming a fabric, and a binding material forming a matrix surrounding the fiber portion embedded within the metallic portion. The fiber portion may be attached to or form part of a composite vehicle component. The transition structure may join a metallic component and a composite component. The transition structure may be manufactured by creating first channels within a layer of a metallic substrate, inserting fiber tows into the first channels, placing a first metallic layer over the metallic substrate and the fiber tows, consolidating the metallic layer to the metallic substrate, and binding the fiber tows within a resin. Prior to binding, additional layers of channels and fiber tows may be consolidated onto the first metallic layer.

A transition structure includes a metallic portion, a fiber portion including a plurality of tows embedded within the metallic portion and extending out from the metallic portion forming a fabric, and a binding material forming a matrix surrounding the fiber portion embedded within the metallic portion. The fiber portion may be attached to or form part of a composite vehicle component. The transition structure may join a metallic component and a composite component. The transition structure may be manufactured by creating first channels within a layer of a metallic substrate, inserting fiber tows into the first channels, placing a first metallic layer over the metallic substrate and the fiber tows, consolidating the metallic layer to the metallic substrate, and binding the fiber tows within a resin. Prior to binding, additional layers of channels and fiber tows may be consolidated onto the first metallic layer.

Provided is an electric resistance welded steel pipe or tube having excellent fatigue durability after rapid and short-time heating quenching treatment. An electric resistance welded steel pipe or tube comprises: a base metal being a steel sheet having a specific chemical composition and an electric resistance weld portion having a bond width of 40×10.sup.−6 m or more and 120×10.sup.−6 m or less, wherein C.sub.0-C.sub.1 is 0.05 mass % or less, where C.sub.0-C.sub.1 is a difference between C.sub.1 in mass % which is a minimum C content of the electric resistance weld portion and C.sub.0 in mass % which is a C content of the steel sheet, and a depth of a total decarburized layer in each of an inner surface layer and an outer surface layer of the electric resistance welded steel pipe or tube is 50×10.sup.−6 m or less.