I had the same thing happen with my BK9, it got wet (fresh water) and the edge started to rust after only about 2 hours. The rusted parts of the edge had lost the ability to shave cleanly, but I was able to restore the edge quickly and easily with a ceramic rod, since the rust was only beginning to take hold.
If the coating is intact, it dose a very good job of preventing corrosion, but the exposed edge needs to be kept clean and dry (and preferably oiled) to keep it free of rust.
- Frank