The pursuit of a truly rust proof knife steel has been a long one. Traditional steels typically pursue rust resistance through increasing amounts of chrome. The trade-off is that more chrome will make a knife rust resistant, but past a certain point, more chrome makes steel harder to take and keep a good edge, and also makes a knife less resistant to impacts ("toughness"). Some blade makers have pursued non-metallic blade materials, but these have all suffered one or more major flaws that prevent widespread applicability.
Japanese H1 steel is a solution just a few knife makers have used. It uses nitrogen in place of carbon. H1 is a precipitation hardened steel, which means that it doesn't get heat treated. H1 has very good toughness for a stainless steel, but doesn't hold an edge as long as many other premium knife steels. According to Spyderco's Sal Glesser, this changes when you serate H1 steel.
The act of serration work hardens the steel, enabling it to take an extremely sharp edge that is durable and long-lasting. Unfortunately, many self-proclaimed knife people don't like serrations as much as plain edges, because they find them harder to sharpen. This won't be a concern on the ARK if someone is using the knife as a dedicated emergency tool. I personally carry the ARK if I'm doing something on water, if perhaps I am exercising and trying to keep my weight at a minimum or I'm not wearing clothes appropriate to hold a heavier knife, or sometimes when I'm in uniform. there is a question about whether defensive knives should only be used for defensive purposes, but that is probably a question for its own thread.
John
