Failure analysis of a diesel engine cylinder head

This paper presents a failure analysis on a diesel engine cylinder head made of grey cast iron, which was used in a truck. The crack initiated from the interior wall and propagated toward the exterior surface of the cylinder head. The metallurgical examination was conducted in the crack origin zone and other zones. The results show that longer graphite flake and more amount of the ferrite are the general metallurgical characteristics of the failed cylinder head, compared with the specified, which may lead to the lower whole hardness of the material. It is important that in the crack origin zone, the abnormal graphite morphology appears in 1.3 mm region below the interior wall. The abnormal graphite mainly exhibits network of grain boundary flake graphite and the graphite flakes connect each other. The appearance of the network grain boundary flake graphite decreases intensely the strength of this zone to initiate the crack in this zone. Moreover, the whole lower strength of material, premature fracture of the cylinder head took place.