Fracture failure of a diesel engine piston-pin

• A diesel engine piston-pin failed during service.
• The longitudinal cracking took place first and then the transverse fracture occurred.
• The banded texture is presented in the middle region of the longitudinal fracture.
• The longitudinal crack originated from the banded texture.
• The banded texture is associated with longitudinal inclusion clusters of excess size.

Longitudinal cracking and transverse fracture took place on a diesel engine piston-pin used in a truck during service. The banded texture throughout the whole length of the longitudinal fracture is presented in the middle region of the longitudinal fracture. The longitudinal crack originated from the banded texture and propagated toward the internal hole surface and the external circle surface of the piston-pin. Metallographic and chemical inspections of the piston-pin material away from the crack origin reveal all the parameters to be acceptable. Subsequent metallographic examinations were performed on the smoothed longitudinal fracture surface. These reveal the presence of the longitudinal inclusion clusters of 25 mm long mainly consisting of calcium aluminate, associated with the banded texture on the longitudinal fracture. Under the integrated action of structure stress and service stress, the crack propagated along the longitudinal first, and then propagating along the transverse by fatigue under the alternative service load. The appearance of longitudinal inclusion clusters of excess size in the crack origin zone is mainly responsible for the failure of piston-pin.