Stress relieved grinding ball having hard outer shell

A process for making a grinding ball having a hardened section of tempered martensite wherein said ball has been stress relieved to stabilize said ball against break up and/or spalling, said process comprising:

• i) reheating a tempered grinding ball having a hardened section of tempered mantensite to its previous equalization temperature of its earlier tempering process;
• ii) holding the grinding ball at the equalization temperature for a period of time sufficient to relieve partially compressive stresses in the tempered martensite section to develop an outer stress relieved martensitic shell and an inner non-stress relieved martensitic section;
• and
• iii) allowing the reheated stress relieved ball to cool.