Thanks! cool to know
Thanks for the pic Max. That helps. That is just normal oxidation. Stainless resists rust by forming a thin coating of oxidation on the surface - similar to a Patina on other metals like copper, bronze, brass. The coating once formed protects the metal.
Carbon steel will look very shiny in comparison (before it starts rusting) and it will not have the INOX stamp on it. Not many manufacturers even produce carbon steel hangers - for example - Metolius and Petzl don't make anything but stainless.
This is not from my favorite source but it does a good job explaining.
Stainless steel differs from carbon steel by the amount of chromium present. Unprotected carbon steel rusts readily when exposed to air and moisture. This iron oxide film (the rust) is active and accelerates corrosion by forming more iron oxide.
Stainless steels contain sufficient chromium to form a passive film of chromium oxide, which prevents further surface corrosion by blocking oxygen diffusion to the steel surface and blocks corrosion from spreading into the metal's internal structure.