The demands on today's military for lighter, cheaper, longer lasting products only increase the risk for catastrophic failure of items already facing adverse service conditions. After a medium caliber barrel failure, the Explosive Sciences Branch (ESB) of Crane Division, Naval Surface Warfare Center (NSWC Crane) performed metallurgical investigations on one damaged gun barrel, six additional barrels pulled from service and one new gun barrel, to determine if any inherent flaws or service conditions could have caused the failure. The metallurgical analysis included detailed microhardness profiling on several areas of each barrel, complete microstructure examination with a metallurgical microscope, crack depth determination via optical comparator, optical microscopy and SEM analyses on down-bore sections of the barrels, and geometrical analysis on the rifling of the barrels. Hardness differences were found between the outside edge and/or inside edge of the barrels versus the center or core of the barrels. Additionally, areas of no chrome coating, cracked coating, base metal cracking, and stress corrosion cracking were evident in the breech end of the barrel, while land damage/deformation was prominent in down-bore barrel sections. The ESB determined coating cracking and slight interface corrosion between the base metal and coating would lead to accelerated degradation (erosion, corrosion, cracking, etc.) of barrels in service. These findings show that many barrels still in use should be pulled from service and that better erosion/corrosion monitoring techniques need to be in place to better assess the condition and risk of barrels in service.
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