Failure Analysis of a Shipping Container Handler Twistlock Pin

During operation of a shipping container handler, a Twistlock pin supporting one side of two stacked shipping containers fractured, causing the shipping containers to fall. An investigation revealed that the alloy steel pin had a ferritic/bainitic microstructure with an average of 29.5 Rockwell C scale hardness and a typical Charpy V-notch impact energy of 17 J at room temperature. Examination of the fracture surface revealed a cleavage fracture that initiated from a quench crack. It was determined that the primary cause of the failure was improper heat treatment.