Although resistant to environmental degradation due to hydrogen, super high strength Cu-Ni-Mn-Al cupronickels (typical proof stress 730 N/mm²) without cathodic protection have been shown to be susceptible to stress corrosion phenomena, when stressed to levels which cause significant plastic deformation, in ammoniacal environments or those in which saline solutions are present at temperatures above 50°C. Stress corrosion of Cu-Ni-Mn-Al is principally manifested by the occurrence of a brittle intergranular fracture morphology which is probably due to the operation of an anodic dissolution mechanism. The presence of large grains in some Cu-Ni-Mn-Al alloys appears to be associated with a greater susceptibility to environmental degradation. Improvements in the manufacturing methods used for alloy production have demonstrated that resistance to these phenomena can be achieved for a Cu-Ni-Mn-Al alloy when used in environments encountered by marine fasteners.