PURPOSE: To improve the corrosion resistance of a hard Cr plated piston rod at a low cost.

CONSTITUTION: The surface of a hard Cr plated piston rod is buffed to form a plastic fluidity layer having ≤0.2μm width of microcracks opening to the surface up to ≥0.2μm depth from the surface of the plating layer. Since this plastic fluidity layer hinders the open air and moisture from penetrating to the base through defects such as microcracks and pinholes in the hard Cr plating layer, the base can be prevented from gathering rust under the open air and moisture and the corrosion resistance of the piston rod can be improved at a low cost.