Abstract: A fillet weld joint of steel formed by arc welding, wherein a martensitic transformation starting temperature (Ms point) of a weld metal is 400° C. or above and 550° C. or below, a value obtained by dividing a toe radius ? of a toe part of welding by a sheet thickness t of a base metal (?/t) is 0.25 or above, an expression Ms(° C.)?375×[?/t]+320 is satisfied, and a crack defect does not exist in the fillet weld joint.

Abstract: Arc welding is performed with a flux-cored welding wire using pure Ar shielding gas with a pulsed current having a peak current of 340 to 540 A and a peak current time of 0.7 to 2.5 ms as a welding current, in which the wire includes a carbon-steel sheath and contains, on a mass percent basis, 0.02% to 0.15% C, 0.30% to 1.50% Si, 0.70% to 2.30% Mn, 0.010% to 0.100% S, 0.01% to 0.18% Ti, 0.030% or less P, and 0.15% or less Cr, with respect to the total mass of the wire, in which the wire has a flux content of 10.0% to 30.0%, the flux has a S content of 0.030% to 0.600%, and the wire satisfies [Sf]>([Sh]+0.010), where [Sf] represents the S content (%) of the flux, and [Sh] represents the S content (%) of the sheath.

Abstract: A fillet weld joint of steel having high fatigue strength by improving stress concentration without excessively relying on imparting a compressive residual stress to a toe part by welding materials, free of cracking, and excellent in the toughness, and a method for gas shielded arc welding for obtaining the fillet weld joint are provided. In the fillet weld joint, a martensitic transformation starting temperature (Ms point) of a weld metal is 400° C. or above and 550° C. or below, a value obtained by dividing a toe radius ? of a toe part of welding by a sheet thickness t of a base metal (?/t) is 0.25 or above, an expression below Ms(° C.)?375×[?/t]+320??(1) is satisfied, and a crack defect does not exist.