Abstract
US Navy uses many metallic materials such as carbon steel, stainless steels, nickel alloys, copper alloys, titanium alloys and aluminum alloys in their ships. Some of the major concerns are pitting/crevice corrosion, ability to weld repair small worn and corroded areas, prevention of galvanic corrosion and reliable usage of high strength fasteners. Even though several stainless steels and nickel-based alloys have shown promise and are used in marine environments, under very severe crevice corrosion conditions, most of these have suffered from localized crevice attack. Fasteners of alloy K-500 have shown to suffer from stress corrosion cracking. Fasteners of alloy 718 have suffered from localized attack. The search for alloys that are essentially immune to localized crevice corrosion attack in marine environments and provide reliable high strength fasteners, led the US Navy to consider Ni-Cr-Mo alloys with the highest combination of chromium and molybdenum in a nickel matrix. One such pure ternary alloy, alloy 59 (UNS N06059) having a typical chemical composition of 59% nickel, 23% chromium, 16% molybdenum and iron levels of less than 1%, appears to have fulfilled this need. Extensive laboratory and field tests by various companies and corrosion laboratories in USA, U.K, Norway and France have shown this alloy to be essentially immune to crevice corrosion attack. Based on the excellent crevice corrosion resistance of alloy 59, the U.S. Navy has selected this alloy for testing a prototype component in a butterfly valve. They have conducted further tests for repair welding applications via electro-spark deposition technology using alloy 59 filler metal as a superior alternative to alloy 625 and C-276. Due to the SCC problems associated with high strength fasteners of alloy K-500, extensive testing of cold reduced bars of alloy 59 to yield strength levels greater than 150 KSI have been initiated. This paper presents a brief description of this alloy’s development, its physical metallurgical characteristics, localized corrosion resistance data from various test programs, data on repair welding techniques with alloy 59 filler metal via electro-spark deposition technology and potential use as high strength fasteners.
