A new C-type alloy (UNS N07022) with a nominal composition of Ni-21Cr-17Mo (wt. %) was recently introduced for applications requiring both corrosion resistance and high strength. The alloy provides excellent resistance to uniform and localized corrosion in both reducing and oxidizing acids. Three material conditions have been identified that provide much higher strength levels compared to the standard annealed condition: annealed + aged, cold-worked, and cold-worked + aged. The aging heat treatment results in the formation of long-range ordered domains of the Ni2(Cr,Mo) phase. Yield strengths exceeding 200 ksi (1379 MPa) have been achieved for both cold-worked and cold-worked + aged bar. Among the potential applications of the new alloy are high-strength fasteners for use in marine environments. Tensile and Charpy impact properties have been generated for cold-pilgered bars of various diameters. Additionally, a series of slow strain rate tests (SSRT) were conducted to evaluate its environmental cracking resistance in salt water conditions. A program to determine the alloy’s resistance to crevice corrosion under long-term exposure to seawater has also been initiated. Overall, the results show that the new alloy is an excellent candidate for high-strength marine fastener applications.

Subject
Marine environments, Materials, Corrosion resistant alloys, Nickel based alloys, Nickel chromium molybdenum alloys, Sodium chloride, Natural seawater, Seawater, Crevice corrosion, Elongation, Corrosion resistance, Fasteners, Alloys
Keywords:
nickel-base alloys, marine fasteners, corrosion resistance, age-hardenable, high strength
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2012
Association for Materials Protection and Performance (AMPP)
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