Mechanical Properties and Fracture Toughness Assessment of M795 and M549 155 mm Artillery Projectile Bodies Manufactured from HF-1 Steel

This work assesses the mechanical properties and fracture toughness of two 155mm HE artillery projectile bodies as part of a process of ensuring safety during launch and rough-handling. The high-fragmentation steel conformed to MIL-S-50783 HF-1, and specimens were derived from US projectiles M795 and M549 Rocket Assisted Projectile. Arc-tension, AT, tests established that the fracture toughness K sub Ic of the M549 projectile body had been correctly heat-treated to produce a fully martensitic microstructure, while the M795 projectile body was incorrectly heat-treated resulting in a large volume fraction of non-martensitic transformation products. For the M549 body, fracture toughness values determined using AT specimens agreed well with values reported elsewhere determined using Charpy-sized three point bend 3PB specimens. For the M795 body, however, good agreement was obtained for fracture toughness values determined at -40 C using both AT and 3PB specimens while room temperature fracture toughness values determined using AT and 3PB specimens vary significantly because the dimensions of the 3PB specimens were inadequate to obtain valid K sub Ic values.