Effect of fatigue damage on the dynamic fracture toughness of En-8-grade steel

Machine components normally experience fatigue cycling during operation. Fa ilure of these components is mostly due. to fatigue. So, it is important to know the fatigue damage behavior and fatigue life of the material before s electing these steels for making different machine components. The En-8-gra de (equivalent to SAE/AISI 1040) steel is generally used as a machine compo nent in the annealed or hardened-and-tempered condition. The fatigue life ( fatigue/endurance limit) is also dependent upon the tensile properties of a ny material. By suitable heat treatment, one can manipulate the tensile pro perties of any steel. The present work reports the effect of fatigue damage in En-8-grade heat-treated steel (annealed and hardened and tempered), und er different cyclic loading conditions at room temperature (25 degreesC), o n the impact and dynamic fracture-toughness properties. The results indicat e higher fracture toughness and impact toughness in hardened-and-tempered s teel than in annealed steel. Cyclic hardening and softening occurs in both the hardened-and-tempered as well as the annealed steel. With the increase of peak stress and number of fatigue cycles, the K-1D and CVN values decrea se in hardened-and-tempered steels. The results are discussed in, terms of dislocations, slip bands, and their density, microstructure, and fracture m orphology.