Claims
- 1. 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 martensite 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.
- 2. A process of claim 1, wherein said ball has a chemistry of:
- 3. A process of claim 1 wherein said equalization temperature is in the range of about 100° C. to 3000° C.
- 4. A process of claim 3 wherein said equalization temperature is about 150° C.
- 5. A process of claim 1, wherein said ball has a diameter greater than 8 cm where stress relieving of said martensitic section stabilizes said ball against break up as caused by balancing circumferential stresses in a pearlitic core exceeding the tensile strength of the core.
- 6. A process of claim 5 wherein said reheating step at equalization temperature for said tempered ball results in minimal hardness reduction in said tempered martensitic shell.
- 7. A process of claim 1, wherein said ball has a diameter less than 8 cm where stress relieving of said martensitic section to produce said stress relieved martensitic shell reduces spalling.
- 8. 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 by developing an outer stress relieved martensitic shell.
- 9. A grinding ball of claim 8 wherein said martensitic shell has a hardness of 55 to 65 Rockwell C.
- 10. A grinding ball of claim 9, wherein said martensitic shell has a hardness of 60 to 65 Rockwell C.
- 11. A grinding ball of claim 8 wherein said ball has a chemistry of:
- 12. A grinding ball of claim 8, wherein said ball is less than 8 cm in diameter and said martensitic section extends to ball core.
- 13. A grinding ball of claim 8 wherein said ball is greater than 8 cm in diameter and said stress relieved martensitic section reduces circumferential internal compressive stresses in the outer martensitic section and thereby stabilizes said ball against break up as caused by balancing tensile stresses in the pearlitic core exceeding the tensile strength of the core.
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional Application No. 60/175,231, filed Jan. 10, 2000.
Provisional Applications (1)
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Number |
Date |
Country |
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60175231 |
Jan 2000 |
US |