Hey moosecaca (nice handle),
I'm an ex-boat builder so I have a couple of thoughts for you. As far as steels for a dive knife, No. 1 would be M390, with 20% Cr, and 4 % Vanadium. No. 2 would be Elmax, with 18% Cr and 3% Vanadium. No. 3 would be 440C with 17% Cr and no Vanadium. No. 1 and 2 are both particle metals, which are far superior to cast metal in the high alloy stainlesses. Of course, No. 1 is more expensive than No. 2, which is more expensive than No. 3. The only place I could find which stocks Nos. 1 & 2 is usaknifemaker.com. These opinions are just mine, others may differ.
Boat builders solved the problem of attaching dissimilar materials for underwater use long ago. The first method is to allow the knife to be disassembled and rinsed in fresh water after use. The other method is a little more complicated, but, IMHO, much better. First, clean the scales and tang with denatured alcohol several times to insure there is no oil from your fingers or other contamination. Next, decide which type of connectors you want to use to attach the scales. I like to use Corby bolts, made of SS. Do not use brass, because it will dezincify over time. Smear about a 1/16" thick layer of 3M-5200 (do not use the quick cure - use the type which takes about a week to fully cure) on each mating surface, ie each side of the tang and the mating side of each scale. Assemble and tighten the corbys until there is an even amount of 5200 extruded all around the mating surfaces. DO NOT OVERTIGHTEN. Let the knife sit for 7 days until the 5200 is fully cured. Use a razor blade to trim off the excess. Tighten the corbys maybe a 1/2 turn until a little more 5200 extrudes and stop. Trim off the new excess and you are done. This will give you a joint which is impervious to water and will allow expansion and contraction due to temp change.
Ordinarily, I would use G-flex, but for a knife which may see continuous immersion, 3M-5200 is better.
Tim
