Mechanical components can have a longer fatigue life than that conventionally established in 10(7) cycles. Ultra-High Cycle Fatigue (UHCF) has assumed great significance after it has been established that a fatigue limit does not exist in many cases. This project aims to determine the fatigue life, in mega and gigacycle regime, of structural steel used in the manufacture of a crankshaft and to study the influence of metallurgical inhomogeneities on strength fatigue. Experimentally, specimens meeting the boundary conditions for ultrasonic tests, will be machined from the same material of the crankshaft that failed in operation. Given the mechanical properties of the material (elasticity modulus, yield limit, mechanical strength and density), the UHCF specimens will be subjected to 10(7) – 10(9) cycles, at an ultrasonic frequency of 20 kHz at Laboratório de Fadiga de Altíssimo Ciclo da PUC-Rio. With the tests completed and the data obtained, analyzes will be done in order to better understand this new regime.