Failure Analyses of Ductile Cast Iron Crankshaft in a Diesel Engine

The failure analyses were conducted on a diesel engine crankshaft made of ductile cast iron,which was nitrided.The fracture occurred at the web between the 1st crankpin and 2nd journal.The fracture surface was observed in detail by visual and SEM.The bending fatigue fracture was the main failure mechanism of the crankshaft.The chemical composition,mechanical properties and microstructure of the crankshaft material were within the specified ranges.The over-shallow nitrided layer formed at the surface of the crankshaft should be responsible for the fracture of the crankshaft.