Use of high energy density beam butt welded joints

Welded joint of the present invention includes: a pair of steel, and the weld metal, formed in the butt weld between the steel pair is formed by high energy density beam welding; wherein, by the use of the seam calculated by the following equation (a) mass% of a metal phase composed of the following transformation start temperature Ms is 250 ℃, Ms (℃) = 371-353C-22Si-24.3Mn-7.7Cu-17.3Ni-17.7Cr-25.8 Mo (a).