Elmax has pretty good rep, and it's been around for a while...
Remember a thread on BF of someone making quite large knife from Elmax to customer specs and soaking the offcuts in salty water without the steel not rusting...
My point though is that with res-c handle after diving there's going to be water under the res-c and steels in strict sense (iron+carbon) will eventually rust.
H1 will not because it doesn't have any carbon in it.
Plus sea water is not the same as tap water with some salt in it...