Treatment process for a central bore through a centrifugal compressor wheel to create a deep cylindrical zone of compressive residual hoop stress on a fractional portion of the bore length, and compressor wheel resulting therefrom

An article produced by a process comprising the steps of:

• providing a centrifugal compressor wheel fabricated of a ductile metal having a tensile yield strength, the compressor wheel comprising a hub and a plurality of blades joined to the hub and extending radially outwardly from the hub, each blade having a blade root fillet where the blade joins with the hub, the compressor wheel having a first face and an opposite second face, the hub of the compressor wheel defining a bore that extends centrally through the hub along a downstream axial direction, the bore having an axial length;
• selecting a fractional portion of the axial length of the bore defined between a starting point and an ending point of said fractional portion, wherein the starting point is spaced axially downstream from the first face of the compressor wheel and the ending point is spaced axially downstream from the starting point;
• and
• cold working the metal at an inner surface of the bore beyond the tensile yield strength in a hoop-wise direction about the bore, along only said fractional portion of the bore, the bore not being cold worked outside said fractional portion, so as to induce compressive residual hoop stresses in the metal adjacent the inner surface along said fractional portion, such that the compressor wheel comprises a cold-worked zone of residual compressive hoop stresses in a relaxed state of the compressor wheel, said cold-worked zone extending radially outwardly from an inner surface of the bore and extending axially along said fractional portion of the axial length of the bore.