51312-01634-A Viable Ni-Cr-Mo Alloy for High-Strength Marine Fastener Applications

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Product Number: 51312-01634-SG

ISBN: 01634 2012 CP

Author: Jeremy L. Caron

Publication Date: 2012

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A new C-type alloy with a nominal composition of Ni-21Cr-17Mo (wt. %) has recently been 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 + age-hardened cold-worked and cold-worked + age-hardened. The aging heat treatment results in the formation of long-range ordered domains of the Ni2(CrMo) phase. Yield strengths exceeding 200 ksi (1379 MPa) have been achieved for both cold-worked and cold-worked + age-hardened bar. Among the potential applications of the new alloy are high-strength fasteners for use in marine environments. 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 sea water has been initiated. Tensile and Charpy impact properties have been generated for cold-pilgered bars of various diameters. Additionally elevated temperature and long-term aged tensile results will be presented. Overall the results show that the new alloy is a viable candidate for high-strength marine fastener applications.