Failure Analysis on Diesel Engine Exhaust Valves

Failure analysis was conducted on two diesel engine exhaust valves manufactured by joining martensitic and austenitic steels (stem and head parts, respectively). While one of these valves failed by cracking, the other one failed by fracture from the austenitic steel head. Microscopic and spectroscopic examinations conducted on the cracked valve revealed evidences of overheating-induced oxidation (i.e., burning). In the case of the fractured valve, observation of beach marks on the fracture surface suggested the progress of failure via fatigue following burning.