How does a relatively small amount of chromium prevent steel from rusting?

Question

How does a relatively small amount of chromium prevent steel from rusting?

In: 573

Answer 1

The chromium does rust, but the difference is chromium rust (chromium oxide) stays strong and bonds to itself and the iron and so it doesn’t flake off like regular iron rust, and this layer of strong chromium rust prevents oxygen from reaching the iron underneath. Iron rust (iron oxide) however is very weak and thus it flakes off exposing non-rusted iron, allowing oxygen to rust more iron. Hope this explains it in a simple yet smart way :))