1. Introduction
In application of steel materials, while development
of steel materials is solely important, progress in welding
technologies making good use of advanced steel
materials is also necessary and indispensable. In recent
years, high tensile strength steels have progressively
replaced mild steel, as exemplified by increasing application
of ultra-high strength steels and the tendency of
this innovation has been conducted with managing compensated
formability and weldability of selected materials1).
Progress in welding technologies adopting these
materials is strongly demanded in order to make the best
use of these high tensile strength steels and establish a
global position of technological superiority. The requirements
in the automotive field are extremely stringent, in