A connecting cap from a truck engine fractured after 65,200 km (40,500 mi) of normal service. The cap was made from a 15B41 steel forging and was hardened to 29 to 35 HRC. Visual examination of the fracture surface disclosed an open forging defect across one of the outer corners of the cap. The defect extended approximately 9.5 mm (3/8 in.) along the side of the cap. The fracture surface exhibited beach marks typical of fatigue. The surface of the defect was stained, indicating that oxidation occurred either in heat treatment or in heating during forging. Deep etching of...