Structural steel friction stir joining method for manufacturing a bonded joint of steel structures and methods

Object of the present invention is when the friction stir welding structural steel, advantageously eliminate undesirable plastic flow is caused by insufficient heating of the workpiece, and to achieve sufficient strength to achieve improved workability in joining. In the present invention, a configuration in which, when the friction stir welding structural steel, sheet metal working to become the material (3) by using a heating means (5) in front of the rotary tool (1) of embodiment preheating heat treatment process, strict control of the surface temperature of the heating zone in the preheating process, size, position, etc., of the rotary tool (1) is moved in the engagement direction.