A PURE TERNARY HIGH MOLYBDENUM CONTAINING NI-CR-MO Alloy UNS N06059 (Alloy 59) PROVIDES RELIABLE SOLUTIONS TO VARIOUS MAINTENANCE AND CORROSION PROBLEMS IN NAVAL/MARINE APPLICATIONS

摘要

US Navy uses many metallic materials such as carbon steel, stainless steels, nickel alloys, copper alloys, titanium & aluminum alloys in their ships. Some of the major concerns are pitting/crevice corrosion, stress corrosion cracking, hydrogen embrittlement, 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, including high alloys like alloy 625 and alloy C-276. Fasteners of alloy K-500 have failed due to stress corrosion cracking. Alloy 718 fasteners suffer from localized attack. The search for alloys that are essentially immune to crevice corrosion attack in marine environments and provide reliable high strength fasteners for replacing K-500 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 including testing by the US Navy, U.K., Norway and France have shown this alloy to be essentially immune to crevice corrosion attack in natural sea-water, artificial sea-water and chlorinated sea-water. 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 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 recaps some of the earlier work done by the author's company and by the US Navy engineers on this alloy. Some concerns were raised regarding the galvanic compatibility of cold reduced bars of alloy 59 with other materials used in submarines construction such as HY80 steel and K500 plates. The data from this test program is also presented in this paper along with some other data.