Analysis of Failure of Pin Locator for Internal Nose Cap of a Long Range Cruise Missile

A steel pin used as a locator for internal nose cap of long range cruise missile was found in cracked condition after it was subjected to transportation, vibration and bump tests. Metallurgical investigation was carried out with the failed pin. The crack was found to be inter-granular and a thin black oxide layer was observed on the fracture surface. Based on the evidence, it is concluded that the pin failed because of quench cracking and the crack was initiated prior to tempering and zinc plating.