Failure Analysis of Marine Engine Crankshaft

The crankshaft of a marine engine breaks after less than 2 years operation. Failure analysis was carried out by means of mechanical property test, chemical composition analysis, metallographic analysis and fracture observation. Analysis shows that the reason for the fracture of crankshaft is that the inclusion of large-scale protective slag in the crankshaft caused by the inclusion of protective slag in the process of casting, which destroys the continuity of crankshaft material and reduces the bearing capacity of crankshaft and the crankshaft produces fatigue crack when working. The heat treatment and nitriding of the crankshaft did not meet the requirements of the drawings, which further reduced the fatigue strength of the crankshaft and accelerated the fatigue crack growth. With the crack growth, the fracture finally occurred.