PURPOSE: To prevent the occurrence of abnormal peeling at the rolling surface of a fixed side bearing ring and to improve bearing characteristics by applying work hardening treatment to the surface of a steel ball and specifying the value of residual tensile stress of the surface layer in the direction of depth.

CONSTITUTION: The surface of a steel ball used for grease sealed bearing is subjected to work hardening, and the difference in hardness between the inner part and surface layer of the steel ball is regulated to ≥HRC1. In the above steel ball, the residual tensile stress of the surface layer in the direction of depth is regulated to a maximum of ≤150MPa, preferably 50-150MPa. By this method, the occurrence of abnormal peeling due to hydrogen can be prevented, and this steel ball can contribute toward the increase in the aptitude for bearing.