It depends on how "high strength" you want to get. I normally use 316 stainless hardware and have had no adverse results in long time seawater immersion. You have to use anti-seize at assembly to prevent galling at the contact point of the threaded portion. Also put anti-seize under the head of the bolt and the friction face of the nut where they contact the flat washer to prevent galling at this surface. Stay with Nyloc nuts, lockwashers do not stand up to sea water at all. DO NOT use all-metal locknuts, the friction area on-all metal locknuts galls immediately. Normal stress corrosion would occur first where the galling occurred so prevention is necessary. Probably top of the line for really "high strength" stainless hardware will necessitate going to Nitronic 50 or something similar. I am currently specing N50 hardware for rotating machinery on the weather decks of U.S.Navy ships. Strength comes from strain hardening which is an invitation to stress cracks and subsequent corrosion so don't harden the material anymore than needed to achieve whatever strength you require. Hope this helps. You can e-mail me direct if you want or keep going through here, whichever is more convenient for you.
John S. Crowe
johnscrowe@worldnet.att.net
