Most DE razors are made of brass (or aluminum, for some Weishi's, or plastic for some really inexpensive models). The brass razors are plated with chrome and/or nickel. They don't rust.

The blades, now, are mostly stainless steel -- they don't rust either.

Rust is a real problem for straight razors, mostly made of non-stainless, high-carbon steel. But not for DE's.

Charles