The present disclosure belongs to the technical field of welding materials, and in particular relates to a Fe—Ni based alloy welding wire for welding 800H alloy and a preparation method thereof and a method for welding 800H alloy. The Fe—Ni based alloy welding wire for welding 800H alloy provided by the present disclosure has a reasonable chemical components, and after being used to weld 800H alloy, the obtained weld has a tensile strength of 557.6 MPa and an elongation of 37.5% at ambient temperature, and has a tensile strength of 420 MPa and an elongation of 17.25% at a temperature of 650° C.

A flux-cored wire including a sheath and a flux that fills the sheath, wherein the flux includes a titanate and a nanoparticulate oxide selected from the group consisting of TiO.sub.2, SiO.sub.2, ZrO.sub.2, Y.sub.2O.sub.3, Al.sub.2O.sub.3, MoO.sub.3, CrO.sub.3, CeO.sub.2, La.sub.2O.sub.3 and mixtures thereof.

A welding flux including a titanate and a nanoparticulate Niobium compound chosen from among Niobium oxides, alkali niobates and mixtures thereof.

A flux-cored wire according to an aspect of the present invention includes: a steel sheath; and a flux filling the inside of the steel sheath, in which the flux contains 0.11% or more in total of a fluoride in terms of F-equivalent value, 4.30% to 7.50% of a Ti oxide in terms of TiO.sub.2 equivalent, 0.30% to 2.40% in total of an oxide in terms of mass %, and 0% to 0.60% in total of a carbonate in terms of mass %, the amount of a Ca oxide in terms of CaO is less than 0.20% in terms of mass %, the amount of CaF.sub.2 is less than 0.50%, a chemical composition of the flux-cored wire is within a predetermined range, a Z value is 2.00% or less, a V value is 5.0 to 27.0, and Ceq is 0.30% to 1.00% or less.

Provided is a stainless steel flux-cored wire for manufacturing an LNG tank. From the stainless steel flux-cored wire, it is possible to obtain a weld metal having excellent tensile strength and impact value by adjusting the contents of Mn, Mo, and Cr. The stainless steel flux-cored wire is applicable to welding of 9% nickel steel, high manganese steel, and stainless steel materials and can provide a weld metal having excellent cryogenic toughness in a weld zone because the contents of Mn, Mo, and Cr are adjusted.

A Ni-based alloy flux-cored wire includes the contents of Mn and Nb that are adjusted so that, from the wire, it is possible to obtain a weld metal having an excellent bead shape, good arc stability, spattering inhibition effect, good strength, good defect resistance, and good crack resistance. The Ni-based alloy flux-cored wire produces a weld metal having an excellent bead shape in multiple position welding of Ni-based alloy, 9% Ni steel, and high corrosion-resistance austenitic stainless steel, and an effect of producing a weld metal having good strength, defect resistance, and crack resistance.

A flux-cored wire may be used with an Ar—CO.sub.2 mixed gas, the wire having a steel sheath filled with a flux. Such flux-cored wires may include, as a total of the steel sheath and the flux, relative to a total wire mass: Fe in 92 mass % or more, total Si in a 0.50 mass % or more and 1.50 mass % 15 or less, Mn in 1.00 mass % or more and 3.00 mass % or less, total Li in 0.010 mass % or more and 0.10 mass % or less, and total Mg in 0.02 mass % or more and less than 0.50 mass %, C in 0.15 mass % or less, P in 0.030 mass % or less, S in 0.030 mass % or less, and a slag forming agent in 0.50 mass % or less.

A stainless-steel welding wire for use in manufacture of an LNG tank is described. From the welding wire, it is possible to obtain a weld metal having excellent tensile strength and impact value because the contents of Ni, Mn, Mo, and Cr in the welding wire are adjusted. The welding wire can be applied to welding of all of 9% nickel steel, high manganese steel, and stainless-steel materials by adjusting the content relationship of Ni, Mn, Mo, and Cr, and has the effect of obtaining a weld metal with excellent ultra-low temperature toughness in the weld zone.

A flux-cored wire according to an aspect of the present invention includes: a steel sheath; and a flux filling the inside of the steel sheath, in which the flux contains 0.11% or more in total of a fluoride in terms of F-equivalent value, 4.30% to 7.50% of a Ti oxide in terms of TiO.sub.2 equivalent, 0.30% to 2.40% in total of an oxide in terms of mass %, and 0% to 0.60% in total of a carbonate in terms of mass %, the amount of a Ca oxide in terms of CaO is less than 0.20% in terms of mass %, the amount of CaF.sub.2 is less than 0.50%, a chemical composition of the flux-cored wire is within a predetermined range, a Z value is 2.00% or less, a V value is 5.0 to 27.0, and Ceq is 0.30% to 1.00% or less.

The present invention relates to a flux-cored wire for positive polarity gas-shielded arc welding use, in which a flux contains a metal powder and also contains BaF.sub.2 and SrF.sub.2 and AlF.sub.3 and/or CaF.sub.2 as fluorides wherein the content of BaF.sub.2 is 1.0 to 4.5%, the content of SrF.sub.2 is 2.0% or less, the content of CaF.sub.2 is 0.45% or less and the content of AlF.sub.3 is 0.70% or less, at least one of metal elements constituting the flux and the fluorides is a strong deoxidizing metal element having a specified standard formation Gibbs energy, and the content of each of an oxide and a carbonate in the flux is 0.5% or less.