Abstract: To provide a super-high strength line pipe that is excellent in low temperature toughness, can be field welded easily, and has a tensile strength of at least 900 MPa (exceeding ×100 of the API standard), and a production method thereof. The present invention relates to a super-high strength line pipe produced by shaping a steel plate into a pipe shape and arc welding seam portions, the strength of a base steel portion is 900 to 1,100 MPa and the strength of the weld metal is higher than the base steel strength −100 MPa. In the steel pipe, the Ni content of the weld metal is higher by at least 1% than that of the base steel. The combination of the chemical components of the steel plate with those of the weld metal, for accomplishing these steel pipes by a U&O step is shown concretely. A production method of the steel plate and the welding method for achieving the steel pipe are also described.

Abstract: In order to conduct welding so that the welded steel shows a decreased residual stress after welding without a post treatment such as a PWHT, the steel for welded structures and the welding wire of the present invention starts a transformation from austenite into martensite at a temperature (Ms temperature) from at least 200° C. to up to 350° C., and has a yield strength from at least 60 kg/mm2 to up to 120 kg/mm2 at the transformation starting temperature. The multipass welding process of the present invention comprises forming a weld metal having a Ms temperature of 150° C. to 300° C., and TIG remelt-run welding the surface of the final layer.

Abstract: To form a weld metal having improved hot cracking resistance, low temperature cracking resistance, toughness, strength, and corrosion resistance when welding high Cr steels containing 7.5 wt % or more Cr, the filler wire of the present invention has the ratio of Cr equivalent/Ni equivalent of 1.8 to 2.8 and the product: of Cr equivalent.times.Ni equivalent of 100 to 140, where Cr equivalent=Cr+Mo+1.5 Si, Ni equivalent=Ni+0.5 Mn+30C; and forms a weld metal having a ternary phase microstructure composed of austenite, ferrite and martensite phases during the gas-shielded arc welding. The filler wire of the present invention typically consists of 0.005-0.12 wt % C, 0.01-1.0 wt % Si, 0.02-2.0 wt % Mn, 12.0-17.0 wt % Cr, 5.0-8.0 wt % Ni, 1.0-3.0 wt % Mo, and the balance of Fe and unavoidable impurities, the impurities including 0.03 wt % or less P and 0.01 wt % or less S.

Abstract: Titanium having a thermal shrinkage factor close to that of Nb.sub.3 Sn superconducting wire, whereby it gives rise to little degradation of the properties of the superconducting wire and also offers a good balance between strength and toughness at liquid helium temperature, making it highly suitable as a conduit pipe material used as a seal for liquid helium for high-magnetic-field superconducting coil applications. The present invention focusses on the major effect on strength and toughness of titanium material that the oxygen content has, and appropriately controls the oxygen and other impurities content of pure titanium to provide titanium material comprising, in mass %, 0.07 to 0.13 percent O, up to 0.10 percent Fe, up to 0.10 percent C+N, and up to 0.