In large part this depends on the amount of carbon added to a knife, a substance you also need to make sure a knife is, and stays, sharp.
There is, however, a knife with a blade made from Japanese H1 steel, that is actually stainless, even in seawater, which is known to be an extremely corrosive medium.
The carbon element in this metal was mostly replaced by nitrogen, and the final result is a great knife comparable to normal types of good-quality steel knives, which doesn't rust.
Of course the other metals parts are also completely stainless.
Rust does not only cosmetically affect the blade; if rust emerges on the edge of the knife, it loses its sharpness.