Originally Posted by
choddo
This seems surprising with no salt present? They definitely weren’t there before?
I've had low-alloy steels rust in seconds. Cleaned a new carbon steel pan of wax before heat-bluing, it started to get a thin film of rust within seconds out of the wash water.
Having some alloying elements, like even a little chrome, will make it rust slower. A lot of chrome, like over 13%, and it's "stainless" steel, very corrosion resistant. Typical files don't rust instantly, due to the alloying elements added, not for corrosion resistance, but to increase hardness without becoming too brittle, as you get if all hardness comes from addition of carbon.