Was just wondering whether any of you fine smiths on here have ever been commissioned to make a dive knife, I'm a keen diver and rather fancy a special knife I've made myself, but am unsure what materials and processes I should be looking at, considering the exposure to salt waters and such..

Any help greatly appreciated    

If it was me, I would lean towards a nitrogen stainless steel. Anything else can still rust in salt water.

http://www.alphaknifesupply.com/zdata-bladesteelS-N680.htm

Wow.. I was looking at the 420 and 440 series but for the ease of manufacture and the corrosion resistance that looks like a perfect choice..

Unless you are setup with a kiln and Liquid Nitrogen, I would send it out to get heat treated.

As fun as liquid nitrogen sounds, I feel like even for me, messing with that might be foolish..

By the way Ben, liking the look of the pig sticker, how does the elmax machine?

Its pretty tough, about .002" at a time.

I suppose at least the adage of measure twice, cut once holds true at a pass of that depth haha..

Nonetheless, you have more patience than me!

Setup and measuring took longer than milling. .002 at about 15-20 secs a pass, only milled to .050 depth. It only took about an hour or so to do the math, measurements and milling.

That is pretty interesting right there Ben?  Never heard of such a thing.  I do know that Titanium is used in dive knives for corrosion resistance and works pretty well.  Depending on your desired performance and use a dive knife really needs very little in the way of HT as it is best left somewhat soft and used more for prying and such with a serrated portion available to cut rope, fishing line, etc. Blunted tips and avoiding really sharp pointy things is good in deep cold water with heavy gear on.

I've not worked the stuff but I have a Matt Diskin assisted opening folder I bought several years ago made from Aus8 steel. It has been in the ocean hundreds of times with no rust. I rinse and oil it after it's been in salt water and it holds a pretty decent edge also. Not sure about the HT and temper though...