Brittle Failure of a Hook Initiated at a Pre-existing Defect

Abstract

A mild steel hook that was part of the auxiliary hoist of an electric overhead crane used in a foundry was of the shank type and the rated safe working load was 15 tons. Failure took place in a wholly brittle manner, and occurred transversely through the back of the hook. From the direction in which the fracture developed, as indicated by the radial lines on its surface, it was evident that a preexisting defect served to initiate the brittle fracture. Material adjacent to the fracture was decarburized and contained numerous globules of oxide and slag. It was evident, therefore that a fissure was formed during the manufacture of the hook and had not developed in service. The failure was associated with a surface defect, and it was recommended that the other similar hooks at the establishment be crack detected and any similar discontinuities eliminated.