Study of a Stud Bolt Wrench Failure Due to an Inadequate Heat Treatment

In this investigation, the failure of a stud bolt wrench was studied. In order to determine the failure cause, the fractured wrench was compared with an un-failed wrench from the same production batch. Chemical analyses, metallographic studies and measurement of mechanical properties were carried out. SEM images were obtained near the crack onset and a brittle fracture was determined. The chemical analyses revealed a very similar composition for both wrenches. In contrast, the tensile tests showed differences in the mechanical strength, which was confirmed by differences in the hardness values measured along the wrench’s longitudinal section. Finally, metallographic analyses showed different microstructures in both wrenches. Therefore, it was concluded that the failure cause was an inadequate heat treatment, which took place during the fabrication process.