A wire dot printer head comprising a leaf spring welded to an armature and biased by a permanent magnet, and a magnetic coil adapted to erase the magnetic field of the permanent magnet so as to release the leaf spring and to drive a print wire. The leaf spring is made of an alloy which consists essentially of 13-14 wt % Cr, 0.37-0.43 wt % C, 0.25-0.5 wt % Si, 0.3-0.5 wt % Mn, 1.15-1.35 wt % Mo and the balance Fe. The alloy makes the width of the weld metal of the leaf spring wide and its depth of weld penetration deep and thus minimizes the generation of micro-cracking.