system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does a relatively small amount of chromium prevent steel from rusting?
gpt
Because it rusts instead.

Stainless steel is about 10% chromium. And when exposed to the air the chromium reacts with the oxygen much faster.

This forms a layer of chromium oxide on the surface. And that layer of chromium oxide stops any more oxygen from reaching the steel (specifically the iron atoms). And since the oxygen can’t reach the iron, it cannot rust.