Abstract: In a flux-cored wire according to the present invention, CaF2 and the like are included and a total amount thereof ? is 3.3 to 6.0% in terms of mass % with respect to a total mass, Ti oxide and the like are included and a total amount thereof ? is 0.4 to 1.2% in terms of mass % with respect to the total mass, CaCO3 and the like are included and a total amount thereof is 0.1 to 0.5% in terms of mass % with respect to the total mass, and an amount of an iron powder in the flux is less than 10% in terms of mass % with respect to the total mass.

Abstract: In a flux-cored wire for welding an ultrahigh tensile strength steel, one or more of CaF2, BaF2, SrF2, and MgF2 are included in the wire and, when a total amount thereof is defined as ?, the ? is more than 2.0% and equal to or less than 8.0% in terms of mass % with respect to a total mass of the wire, one or more of Ti oxide, Si oxide, Mg oxide, and Al oxide are included in the wire and, when a total amount thereof is defined as ?, the ? is 0.01% to 1.20% in terms of mass % with respect to the total mass of the wire, a ratio of an amount of the CaF2 with respect to the ? is 0.50 or more, a ratio of the ? with respect to the ? is 2.0 to 800.0, and Ceq defined in the following expression is 0.60% to 1.20%, Ceq=[C]+[Si]/24+[Mn]/6+[Ni]/40+[Cr]/5+[Mo]/4+[V]/14.

Abstract: In a flux-cored wire according to the present invention, CaF2 and the like are included and a total amount thereof ? is 3.3 to 6.0% in terms of mass % with respect to a total mass, Ti oxide and the like are included and a total amount thereof ? is 0.4 to 1.2% in terms of mass % with respect to the total mass, CaCO3 and the like are included and a total amount thereof is 0.1 to 0.5% in terms of mass % with respect to the total mass, and an amount of an iron powder in the flux is less than 10% in terms of mass % with respect to the total mass.

Abstract: A flux-cored wire for gas shielded welding use which can reduce the oxygen of weld metal to obtain a weld joint which is excellent in toughness and which enables all-position welding by direct current reverse polarity, wherein the wire contains, by mass % with respect to the wire total mass, CaO: 0.2 to 7.0%, one or more of MgF2, CaF2, SrF2, and BaF2 in a total of 1.0% or more (total of fluorides and CaO being 3.0 to 12.0%), one or more of Si, Al (less than 0.3%), Ti, Mg, Zr, Ca, Ce, and La in a total of 0.2 to 2.0%, and one or more oxides of Si, Mn, Al, Ti, B, and Zr in a total of 0.2 to 3.0%, ?=C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+Mo/15+V/10+Nb/10+5B is 0.15 to 0.40%, P and S in a total of 0.040% or less, a balance of Fe, an arc stabilizer, unavoidable impurities, and a content of iron powder in the flux of 5.0% or less.

Abstract: A method of production of a welded joint which enables improvement of the fatigue strength in the case where measures for improvement of the fatigue strength cannot be applied due to the presence of structurally sealed regions is provided. The method is provided with a first weld step which performs welding by forming an inside weld toe or root part by using a weld metal with a transformation start temperature of 175° C. to 400° C. in range, at least parts of the weld metal forming the inside weld toe or root part which was formed at the first weld step becoming unmelted parts, and a second weld step which performs welding for building up the weld metal by a single pass by a weld heat input by which all of the unmelted parts are retransformed to austenite so as to introduce compressive residual stress to the inside weld toe or root part.

Abstract: In a flux-cored wire for welding an ultrahigh tensile strength steel, one or more of CaF2, BaF2, SrF2, and MgF2 are included in the wire and, when a total amount thereof is defined as ?, the ? is more than 2.0% and equal to or less than 8.0% in terms of mass % with respect to a total mass of the wire, one or more of Ti oxide, Si oxide, Mg oxide, and Al oxide are included in the wire and, when a total amount thereof is defined as ?, the ? is 0.01% to 1.20% in terms of mass % with respect to the total mass of the wire, a ratio of an amount of the CaF2 with respect to the ? is 0.50 or more, a ratio of the ? with respect to the ? is 2.0 to 800.0, and Ceq defined in following Expression a is 0.60% to 1.20%, Ceq=[C]+[Si]/24+[Mn]/6+[Ni]/40+[Cr]/5+[Mo]/4+[V]/14??(a).

Abstract: A method of production of a welded joint which enables improvement of the fatigue strength in the case where measures for improvement of the fatigue strength cannot be applied due to the presence of structurally sealed regions is provided. The method is provided with a first weld step which performs welding by forming an inside weld toe or root part by using a weld metal with a transformation start temperature of 175° C. to 400° C. in range, at least parts of the weld metal forming the inside weld toe or root part which was formed at the first weld step becoming unmelted parts, and a second weld step which performs welding for building up the weld metal by a single pass by a weld heat input by which all of the unmelted parts are retransformed to austenite so as to introduce compressive residual stress to the inside weld toe or root part.

Abstract: A flux-cored wire for gas shielded welding use which can reduce the oxygen of weld metal to obtain a weld joint which is excellent in toughness and which enables all-position welding by direct current reverse polarity, wherein the wire contains, by mass % with respect to the wire total mass, CaO: 0.2 to 7.0%, one or more of MgF2, CaF2, SrF2, and BaF2 in a total of 1.0% or more (total of fluorides and CaO being 3.0 to 12.0%), one or more of Si, Al (less than 0.3%), Ti, Mg, Zr, Ca, Ce, and La in a total of 0.2 to 2.0%, and one or more oxides of Si, Mn, Al, Ti, B, and Zr in a total of 0.2 to 3.0%, ?=C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+Mo/15+V/10+Nb/10+5B is 0.15 to 0.40%, P and S in a total of 0.040% or less, a balance of Fe, an arc stabilizer, unavoidable impurities, and a content of iron powder in the flux of 5.0% or less.

Abstract: The present invention provides a flux cored wire for gas shielded arc welding of high-strength steel having proof stress of 690 MPa or more, which is capable of all-position welding with a higher efficiency and exhibits an excellent cracking resistance. The flux cored wire comprising a steel sheath, and a flux filled therein, wherein the flux cored wire comprises, by mass % with respect to the total mass of the flux cored wire: C: 0.03 to 0.10%, Si: 0.25 to 0.7%, Mn: 1.0 to 3.0%, Ni: 1.0 to 3.5%, B: 0.001 to 0.015%, Cr: limited to 0.05% or less, and Al: limited to 0.05% or less, and in the flux, TiO2: 2.5 to 7.5%, SiO2: 0.1 to 0.5%, ZrO2: 0.2 to 0.9%, and Al2O3: 0.1 to 0.4%; and the remainder comprising: Fe, arc stabilizer, and unavoidable impurities; and wherein the total mount of hydrogen in the flux cored wire is in 15 ppm or less.