Abstract
Fasteners of alloy K-500 (UNS # N05500) can suffer from stress corrosion cracking. Fasteners of alloy 718 (UNS # N07718) can suffer from localized attack. The search for alloys, that are essentially immune to localized crevice corrosion attack, in marine environments and can be used as reliable high strength fasteners, led the US Navy to consider Ni-Cr-Mo alloys that have the highest combination of chromium and molybdenum in a nickel matrix. Alloy 59 (UNS N06059), a pure ternary alloy, with the nominal chemical composition 59% nickel, 23% chromium, 16% molybdenum and iron levels of typically less than 1%, appears to have fulfilled this need. Extensive laboratory and field tests by various companies and corrosion laboratories in USA, UK, Norway and France, have shown this alloy to be essentially immune to crevice corrosion attack. Due to the SCC problems associated with high strength fasteners of alloy K-500, extensive testing of cold reduced bars of alloy 59 with yield strength levels greater than 150 ksi has been conducted. Cold reduced bars of alloy 59 have shown excellent resistance to localized corrosion, hydrogen embrittlement and stress corrosion cracking while possessing very high strength, ductility, fracture toughness, high-cycle fatigue resistance and very low crack growth rate both in air and sea-water. This paper presents the results of the various fastener tests, crevice corrosion tests and galvanic compatibility tests in seawater as suggested by the US Navy.
