| Abstrakt: |
Fracture toughness and fatigue studies were conducted on various grades of car-burizing steels. The results indicate that similar or superior mechanical performance can be achieved using the alternate EX grades (EX24, EX29, and EX55) compared to the more commonly used grades (SAE 8620, SAE 4320, and SAE 4817). During the study of fatigue properties, various trends on the influence of surface carbon (re-tained austenite) and carbon gradient (hardness profile and case depth) were observed: 1) increasing the surface carbon to the extent that the hardness profile indicated a max-imum at 0.02 in. (0.5 mm) below the surface severely reduced the endurance limit, 2) changing the hardness profile such that the maximum hardness occurred within 0.010 in. (0.25 mm) of the surface improved the endurance limit, but lowered the impact fracture stress, and 3) increasing the case depth improved the endurance limit. |
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