Metal product surface member and method for burnishing same

A burnishing method for a metal product surface member, the burnishing method comprising:

• using a metal product including a surface having indentations and protrusions formed by blast processing as a treatment target;
• and
• ejecting spherical shaped shot having a lower hardness than a surface hardness of the metal product and a particle diameter larger than a width of the indentation from out of the indentations and the protrusions and having a larger particle diameter than a projection material used for the blast processing against the metal product surface as crushing shot, and causing the crushing shot to collide the metal product surface so as to selectively press and collapse the protrusions from out of the indentations and protrusions formed on the surface of the metal product and improve a surface roughness of the metal product, wherein:
• the metal product serving as the treatment target has indentations and protrusions formed on a surface by ejecting, as an indentation-protrusion forming shot, spherical shaped shot having a hardness that is not less than a hardness of a base material of the metal product serving as the treatment target and selected from a range of an average particle diameter of from 20 pm to 149 pm against the metal product surface;
• and shot employed as the crushing shot has a particle diameter larger than that of the indentation-protrusion forming shot and is selected from a range of from an average particle diameter of from 24 pm to 840 pm.