Electric resistance welded steel pipe securing the high strength and high toughness demanded from oil well pipe in recent years. The metal structure in a region having a width of 0.5 mm in both the thickness directions from a reference point, when using a point defined as a point of the thickness in the thickness direction from the surface in the base material part of the steel pipe as the reference point, consists of polygonal ferrite: 10 area % or less and a balance: bainitic ferrite. The thickness is 15 mm or more.

A spot welded joint of at least two steel sheets is provided. At least one of the steel sheets presents yield strength above or equal to 600 MPa, an ultimate tensile strength above or equal to 1000 MPa, uniform elongation above or equal to 15%. The base metal chemical composition includes 0.05C0.21%, 4.0Mn7.0%, 0.5Al3.5%, Si2.0%, Ti0.2%, V0.2%, Nb0.2%, P0.025%, B0.0035%, and the spot welded joint contains a molten zone microstructure containing more than 0.5% of Al and containing a surface fraction of segregated areas lower than 1%, said segregated areas being zones larger than 20 m.sup.2 and containing more than the steel nominal phosphorus content.

The steel sheet of the present invention has a steel microstructure containing, in area fraction, martensite: 20% to 100%, ferrite: 0% to 80%, and another metal phase: 5% or less, in which, on a surface of the steel sheet, a ratio of dislocation density in metal phases at a widthwise edge of the steel sheet to dislocation density in the metal phases at a widthwise center of the steel sheet is 100% to 140%, and, at a thicknesswise center of the steel sheet, a ratio of dislocation density in the metal phases at the widthwise edge of the steel sheet to dislocation density in the metal phases at the widthwise center of the steel sheet is 100% to 140%. The maximum amount of warpage of the steel sheet when the steel sheet is sheared to a length of 1 m in a rolling direction is 15 mm or less.

Embodiments of the present disclosure are directed to coiled steel tubes and methods of manufacturing coiled steel tubes. In some embodiments, the final microstructures of the coiled steel tubes across all base metal regions, weld joints, and heat affected zones can be homogeneous. Further, the final microstructure of the coiled steel tube can be a mixture of tempered martensite and bainite.

A tool system for stress relieving a turbocharger turbine wheel longitudinally welded to a hardened rotor shaft. The shaft has a journal bearing region and a turbine-end body forming an A datum surface for receiving an axial bearing. The tool system includes an induction coil and an electronic oscillator, and a tool. The tool forms an opening configured to receive the rotor shaft such that the journal bearing region of the shaft extends into the tool housing while the A datum surface adjoins an end of the tool housing. The induction coil is positioned around the turbine-end body. The housing forms an annular cooling chamber surrounding the journal bearing region of the shaft. The housing forms an inlet passage to provide cooling fluid to the annular chamber, and an outlet passage to remove cooling fluid from the annular chamber.

A martensitic steel including the following elements, expressed in percentage by weight 0.1%C0.4%; 0.2%Mn2%; 0.4%Si2%; 0.2%Cr1%; 0.01%Al1%; 0%S0.09%; 0%P0.09%; 0%N0.09%; and can contain one or more of the following optional elements 0%Ni1%; 0%Cu1%; 0%Mo0.1%; 0%Nb0.1%; 0%Ti0.1%; 0%V0.1%; 0.0015%B0.005%; 0%Sn0.1%; 0%Pb0.1%; 0%Sb0.1%; 0%Ca0.1%; the remainder composition being composed of iron and unavoidable impurities caused by processing, the microstructure of said steel having microstructure by area percentage including cumulative presence of residual austenite and bainite between 0% and 25%, the remaining microstructure being martensite at least 70%, and with an optional presence of ferrite between 0% and 10%.

A heat treatment process for a non-quench hardened steel article or friction-welded steel article including normalizing and annealing steps whereby uniformity of microstructure and hardness are significantly improved.

A method of manufacturing tailor welded blanks may be capable of improving a quality of a welded portion and shortening a manufacturing time when a tailor welded blank is manufactured using a coated steel plate. The method of manufacturing tailor welded blanks includes welding one or more pairs of different coated steel plates having different thicknesses or strengths with laser using a filler wire.

Hot-rolled steel sheet having a chemical composition including, in mass %, C: 0.02 to 0.20%, Si: 0.01 to 1.50%, Mn: 0.10 to 3.00%, P: 0.10% or less, S: 0.010% or less, Al: 0.005 to 0.100%, Ti: 0.02 to 0.20%, N: 0.001 to 0.010%, Cu: 0 to 0.50%, Ni: 0 to 0.50%, Cr: 0 to 1.00%, Mo: 0 to 0.40%, Nb: 0 to 0.060%, V: 0 to 1.00%, B: 0 to 0.0100%, Ca: 0 to 0.0050%, O: 0.0100% or less, and the balance: Fe and impurities; in which: a steel micro-structure includes, in area %, ferrite: 60 to 80%, and a total of ferrite and bainite: 90% or more; an average of the crystal grain size of ferrite and bainite is 7.0 m or less, a standard deviation of the crystal grain size is 2.0 m or less; and a standard deviation of a diameter of Ti carbo-nitrides is 10 nm or less.

The present invention relates to a steel material used as materials for building structures, ship structures, offshore structures, or the like and, more specifically, to a steel material having low yield ratio and excellent weld heat affected zone toughness and a manufacturing method therefor.