Abstract: There are provided a laser diode, an irradiating section that applies an output from the laser diode to a base material in the form of a laser beam and thus melts the surface of the base material while moving the laser beam; a wire feeding section that continuously feeds welding wire to a melted portion of the surface of the base material moving along with the movement of the laser beam emitted from the irradiating section; and a wire heating power source that electrifies the welding wire so that the welding wire located in the melted portion of the base material surface is almost melted. In the case of thick plate welding, it is possible to improve operating efficiency and working accuracy, and in the case of welding a hard-to-weld material such as a high-tensile steel board, it is possible to perform welding while preventing deterioration and fracture of metal structure from occurring.

Abstract: A welded joint improved in fatigue strength, a steel deck using the welded joint, and a process of producing the steel deck are provided. A steel deck 3 includes a steel plate 10 having a paving surface 11 on which a pavement is placed, and stiffeners 20 welded to a lower surface 12 of the steel plate opposite the paving surface. Single bevel grooves 22 are formed at respective edges 21 of each stiffener brought into contact with the steel plate, and a weld metal 30 is deposited in each single bevel groove 22. The weld metal is a low transformation-temperature welding material whose martensitic transformation occurs in a predetermined low temperature range. The groove angle ? of the single bevel grooves 22 and welding conditions are set based on data acquired so as to obtain a fixed dilution ratio of the weld metal 30 through control of penetration rate.