The invention relates to a method for producing a high-strength ferritic austenitic duplex stainless steel with the TRIP (Transformation induced plasticity) effect with deformation. After the heat treatment on the temperature range of 950-1150 C. in order to have high tensile strength level of at least 1000 MPa with retained formability the ferritic austenitic duplex stainless steel is deformed with a reduction degree of at least 10%, preferably at least 20% so that with a reduction degree of 20% the elongation (A.sub.50) is at least 15%.

The invention relates to a method for producing a high-strength ferritic austenitic duplex stainless steel with the TRIP (Transformation induced plasticity) effect with deformation. After the heat treatment on the temperature range of 950-1150 C. in order to have high tensile strength level of at least 1000 MPa with retained formability the ferritic austenitic duplex stainless steel is deformed with a reduction degree of at least 10%, preferably at least 20% so that with a reduction degree of 20% the elongation (A.sub.50) is at least 15%.

The present invention relates to a method of manufacturing a pressure vessel.

Provided is a frame member formed by cold-pressing a steel sheet. The frame member has a closed cross section portion in which a cross section perpendicular to a longitudinal direction is a closed cross section, and the closed cross section portion has at least one flat part having a radius of curvature larger than a maximum external dimension of the cross section. A Vickers hardness of a thickness middle portion in a reference flat part is 300 Hv or greater, a width of the reference flat part is 2.0 times or less the effective width, and a standard deviation ratio obtained by dividing a standard deviation of hardness frequency distribution in a surface layer portion in the reference flat part by a standard deviation of hardness frequency distribution in the thickness middle portion in the reference flat part is greater than 1.0.

The chemical composition of a steel material according to the present embodiment consists of, in mass %, C: 0.50 to 0.80%, Si: 1.20 to 2.90%, Mn: 0.25 to 1.00%, Cr: 0.40 to 1.90%, V: 0.05 to 0.60%, P: 0.020% or less, S: 0.020% or less, N: 0.0100% or less, Mo: 0 to 0.50%, Nb: 0 to 0.050%, W: 0 to 0.60%, Ni: 0 to 0.50%, Co: 0 to 0.30%, B: 0 to 0.0050%, Cu: 0 to 0.050%, Al: 0 to 0.0050%, and Ti: 0 to 0.050%, with the balance being Fe and impurities. In the microstructure of the steel material, an area fraction of pearlite is 90% or more, and in ferrite in the pearlite, a volumetric number density of V-based precipitates having a maximum diameter of 2 to 20 nm is 3000 to 80000 pieces/?m.sup.3.

There is provided an exterior panel including a steel sheet, the steel sheet including a flat portion, wherein in an outer-layer region of the flat portion, a microstructure contains, in volume fraction, ferrite of 80% or more, an average grain diameter of ferrite is 1.0 to 15.0 ?m, an intensity ratio X.sub.ODF{001}/{111},S of ferrite is 0.30 or more to less than 3.50, when uEl.sub.1 denotes a uniform elongation measured with a tensile test specimen cut from the flat portion, and uEl.sub.2 denotes a theoretical uniform elongation that is derived from volume fractions, hardnesses, and average grain diameters of ferrite and martensite in a microstructure of an inside region of the flat portion, and a sheet thickness of the flat portion, uEl.sub.1/uEl.sub.2 is 0.44 to 0.80.

A steel pipe has a composition consisting, by mass percent, of, C: 0.12 to 0.27%, Si: 0.05 to 0.40%, Mn: 0.3 to 2.0%, Al: 0.005 to 0.060%, N: 0.0020 to 0.0080%, Ti: 0.005 to 0.015%, Nb: 0.015 to 0.045%, Cr 0 to 1.0%, Mo: 0 to 1.0%, Cu: 0 to 0.5%, Ni: 0 to 0.5%, V: 0 to 0.15%, and B: 0 to 0.005%, the balance being Fe and impurities. As impurities, contents are Ca: 0.001% or less, P: 0.02% or less, S: 0.01% or less, and O: 0.0040% or less. The micro-structure is tempered martensitic or tempered martensite and tempered bainite, in which a prior-austenite grain size number is 10.0 or more. Tensile strength is TS 800 MPa or higher. Critical internal pressure is [0.3TSa] or more, a=[(D/d).sup.2?1]/[0.776(D/d).sup.2], D: pipe outer diameter (mm), d: pipe inner diameter (mm).

To provide a metal wire and an electric wire of high mechanical strength and high ductibility that have sufficiently increased ductibility as well as sufficiently increased mechanical strength. A metal wire manufactured at least by being subjected to an extension in which a metal wire is extended in an axial direction, and having a hardness distribution in which hardness decreases toward a specific peripheral portion from a central portion in a cross-section orthogonal to axis, whereby a softened peripheral portion becomes to show a good malleability as well as a high resistance to cracking, so as to attain an improvement of mechanical strength and ductibility.

To provide a metal wire and an electric wire of high mechanical strength and high ductibility that have sufficiently increased ductibility as well as sufficiently increased mechanical strength. A metal wire manufactured at least by being subjected to an extension in which a metal wire is extended in an axial direction, and having a hardness distribution in which hardness decreases toward a specific peripheral portion from a central portion in a cross-section orthogonal to axis, whereby a softened peripheral portion becomes to show a good malleability as well as a high resistance to cracking, so as to attain an improvement of mechanical strength and ductibility.

The ultra-fine wire fabricating apparatus comprises a feeder assembly, a stationary die, and a rotary die holder. The feeder assembly supplies a wire. The stationary die comprises a hollow inclined channel configured on an inner surface of the stationary die. The hollow inclined channel is configured to receive the wire from the feeder assembly. The rotary die holder configured to receive the wire from the stationary die and simultaneously torsionally deform the wire, wherein the rotary die holder rotates relative to the stationary die to produce the ultra-fine wire with improved mechanical properties. The method ensures continuous grain refinement of wires. The wires are severe plastic deformed using the combined effects of the stationary die and rotary die holder. The mechanical properties of the raw materials are improved due to a grain refinement and microstructure evolution caused by plastic deformation.