Stress corrosion cracking of 4340 steel in aircraft ignition starter residues

Abstract

Military aircraft use a cartridge ignition system for emergency engine starts. Premature failures of steel (AISI 4340) breech chambers in which the solid propellant cartridges are burned is a serious concern. Analysis of a number of breech chamber failures identified corrosion as one problem with an indication that stress corrosion cracking may also be occurring. A study was made for stress corrosion cracking susceptibility of 4340 steel in a paste made of the residues collected from used breech chambers. The constant extension rate test (CERT) technique was employed, and SCC susceptibility was demonstrated. The residues, which contain both combustion products from the cartridges and corrosion products from the chamber, were analyzed using elemental analysis and X-ray diffraction techniques. Electrochemical polarization techniques were also utilized to estimate corrosion rates.